In general, avocado is not threatened by many pests and diseases, and usually, no management measures are applied, making the organic cultivation of the crop possible. Periodically, in my region (Crete, Greece), the increase of thrips population may cause problems and damage the fruits.

Avocado Pests and their Management methods

Avocado Trips (Scirtothrips perseae)

Thrips are a key pest in most orchards worldwide that scars the avocado fruit. The adults are very small (0.7 mm or 0.03 in. long), with an orange-yellow coloring (brown bands on their body and three red dots on the top of the head), and fringed-tipped wings. Its population increases in (late) spring, moving from the foliage to the young fruits. Depending on the temperature (ideally 18-24oC or 65-75 oF), the insect may have more than six generations per year.

While the internal fruit quality is not affected, the insect can severely scar the skin. Almost all damage occurs when fruits are 5–15 mm (0.2 to 0.6 in) long. This “alligator skin” is not commercially acceptable, leading to the avocado’s downgrading (B quality) and extended economic loss for the farmer. Based on experimental results, 3-5 thrips per leaf can cause up to 38% fruit damage. If the population is under control by insects’ natural enemies, or/and slight damage occurs very early in the fruit setting, there is a possibility that the scars will not be so apparent as avocado enlarges (especially Hass avocados).

If the problem persists and pest control is needed, the grower can apply selective insecticides, always after discussing with a local licensed agronomist. Application of products with abamectin can control thrips and persea mites at the same time. Some other practical options are Veratran D + Sugar/Molasses, Success 2 SC + Narrow Range 415 Spray Oil, and Agri-Mek 0.15 EC + Narrow Range 415 Spray Oil (1). However, it is better to protect the natural enemies of the avocado thrip, like predatory thrips (Franklinothrips orizabensis or F. vespiformis) that can generally keep the insect under control. Finally, modifying fertilization and pruning reduces the growth of tender new foliage, which is attractive to thrips (2).

Other common pests of primary concern for avocado are the: Amorbia (Western Avocado Leafroller), Avocado Brown Mite, Greenhouse Thrips, Omnivorous Looper, Persea Mite, Polyphagous Shothole Borer, and Kuroshio Shothole Borer, Sixspotted Mite. Aphids, White Flies, Cutworms, and leaf miners are more likely to become a problem in the avocado plant nursery. Since plants are susceptible to such infestations at the seedling stage, the staff responsible must take all prevention and control measures. Additionally, young avocado plants in the field are in danger from Branch and Twig Borer, European Earwig, False Chinch Bug, Fuller Rose Beetle, Grasshoppers, and June Beetles (3).

In some countries, snails and rodents (like gophers and ground squirrels) may also become a persistent problem for avocado growers. More specifically, gophers can damage sprinklers, divert the irrigation water due to tunnel digging, and damage the young avocado plants. Control by traps is sometimes needed, especially in the first three years of the avocado orchard establishment (4).

The major avocado diseases and how to control them

While no significant problems have been reported in Greece, Phytophthora Root Rot is considered the most common and catastrophic avocado disease, putting global production at risk. At the same time, Anthracnose can cause quality decrease and extensive fruit losses, especially post-harvest.

Phytophthora Root Rot (Phytophthora cinnamomi)

It is the most serious and globally spread disease of avocado, leading to plant death. In some areas of Mexico, the pathogen has infected up to 90% of avocado trees. In Andalusia (Spain), this number is close to 40% (5). The Phytophthora cinnamomi is a soil-born fungus that can infect the plants’ roots that eventually rot. This significantly decreases the capability of the plant to absorb nutrients and water. The first obvious symptom is the development of cachectic and smaller leaves. The plants start losing their leaves, wilt, and eventually die.

The most important preventive measures are the use of healthy, certified plant material and the selection of a variety grafted in a resistant to the pathogen rootstock. The Dusa rootstock is considered one of the most tolerant ones to avocado root rot disease. Excellent level of resistance to Phytophthora cinnamomi exhibits the Duke 7, Toro Canyon, Latas, Martin Grande, Thomas, Uzi (PP15), and Zentmyer (PP4) rootstocks. They are exclusively produced with clonal propagation since the resistance to the pathogen is not transmitted to the new generation by the seed (6).

Prevention is the best and most effective solution since the actual control of the pathogen is extremely difficult and demands a combination of measures (integrated management). Poorly drained and waterlogged conditions accelerate the spread of the diseases and the severity of the symptoms. As a result, it is vital to select well-grained fields to plant an avocado orchard, take all measures needed to ensure that water lodging will be avoided, and prefer controlled drip irrigation of the orchard. Furthermore, good nutritional practices, including sufficient calcium, can be helpful.

If the farmer and agronomist decide that the disease’s chemical control is necessary, the best option is often Phosphonate fungicides (7). The application should be performed on an annual or biannual basis. On the other hand, Metalaxyl (Ridomil) mixed with soil before planting or applied as a soil drench controls root rot at least for four months after treatment (8). Such application can allow replanting of avocado trees (8 weeks after) in a spot with known disease history.

Anthracnose (Colletotrichum gloeosporioides)

This fungal disease can lead to extensive quality loss, especially in warm, humid climates. Some common symptoms are the dry, dark-brown spots that are formed on the fruit skin. In many cases, the symptoms are “masked” by the thick dark skin of some varieties like Hass and are detected only by the consumer that opens the fruit. Spots on the leaves or dead leaves can also be an indication. In severe infections, the farmer can observe abnormal fruit development or fruit drop (9). The disease can spread with the seed, crop residues, and water droplets. Fuerte, Rincon, and Wurtz scion cultivars are very susceptible to the disease (10). In areas with extensive problems, farmers should prefer varieties with thick skin like Sharwil (Guatemalan with some Mexican genes), which has a good tolerance (11).

Management measures include regular sprays (every 2-4 weeks depending on weather conditions) from fruit set initiation until harvest using a registered protectant fungicide such as copper oxychloride. Moreover, the farmer can cut and destroy dead and infected plant parts, prune and harvest only when the conditions are dry, and improve the aeration of the tree canopy. Finally, to avoid disease dispersal and slow down the fruit deterioration, it is essential to cool them down at 5.5 oC (42 oF) after harvest and store them dry (10).

Other common diseases affecting avocado are the: Armillaria Root Rot (Oak Root Fungus), Avocado Black Streak, Bacterial Canker, Branch Canker and Dieback (Formerly Dothiorella Canker), Fruit and Stem-End Rots, Fusarium Dieback, Phytophthora Fruit Rot, Phytophthora Trunk Canker and Crown Rot (Formerly Citricola Canker), Rosellinia Root Rot, Sooty Mold, Verticillium Wilt and Sunblotch (3).

Finally, removing and destroying diseased plant materials can help prevent the spread of many diseases. Most farmers use a fungicide, copper, or azoxystrobin approved for the crop to control many of the diseases mentioned above. The grower should consult an experienced licensed agronomist and follow the manufacturer’s directions for every product.

Avocado Weed Management

Weeds compete with the trees for nutrients and water, while they can host important pests and diseases of the crop. In a healthy, mature, and well-established avocado orchard, weeds do not usually cause significant problems. However, if the plant distances are large and there is a lot of free and sunny space for the weeds to grow, or/and there is water scarcity, the farmer may need to apply weed management techniques. Successfully controlling weeds is vital during the planting of the orchard and at least for the first 3-4 years. The three methods of weed control that are available for avocado are mowing, tillage, and the use of herbicides.

To reduce the nutrient and water losses in my fields, I choose to apply weed control one or two times per year, even in my orchards with older trees. Many fellow farmers use a tractor with a milling machine to destroy weeds. Unfortunately, in most of my fields, the machines cannot move around quickly, and weed control is mainly executed by hand. Especially in new plantations, some growers prefer to apply herbicides. The herbicide can be sprayed three times annually (during February, May, and August for the north hemisphere) (12). In this case, farmers need to be very careful and avoid excessive and careless use to decrease the risk of herbicide-resistant weeds and damage to the avocado trees (caused by using broadleaf target herbicides) (13).

Depending on the region and the field, the species and the populations of the weeds may vary significantly. Some of the most common weeds observed in avocado orchards are: Barnyardgrass, Bermudagrass, Crabgrasses, Puncturevine, Field Bindweed, Longspine Sandbur, Nutsedges, Dallisgrass, and Wild Cucumber. The last two species can be a significant problem for young avocado plants (14). Since many of these weeds reproduce with underground stolons and rhizomes, avoiding using a tractor with a milling machine is recommende because it can chop them into pieces and spread the problem in the entire field quickly. On the other hand, others produce a thousand seeds per plant that can spread and survive in the soil for decades, making their elimination from the field almost impossible. I would advise avocado farmers to scout their fields, recognize the weeds growing, learn about their physiology and then choose the most appropriate weed management strategy.

References

  1. http://www.avocadosource.com/papers/research_articles/hoddlemarkpdf
  2. https://wwwipm.ucanr.edu/agriculture/avocado/Avocadothrips/
  3. https://wwwipm.ucanr.edu/agriculture/avocado/
  4. https://coststudyfiles.ucdavis.edu/uploads/cs_public/b4/3d/b43d58d9-1e91-4a3e-80f9-a2edb14958b0/2020avocadohighdensitysandiegocounty.pdf
  5. https://www.elgo.gr/images/ioanna/periodiko/Teyxos_17/%CF%83%CE%B5%CE%BB._8-10.pdf
  6. https://wwwipm.ucanr.edu/agriculture/avocado/RootstockTolerancetoDisordersandPathogens/
  7. https://www.daf.qld.gov.au/businesspriorities/agriculture/plants/fruitvegetable/fruitvegetablecrops/avocado/pestsanddiseasesofavocadocrops
  8. https://www.fao.org/3/X6902E/x6902ehtm
  9. https://www.jica.go.jp/project/english/kenya/015/materials/c8h0vm0000f7o8cjatt/materialspdf
  10. https://wwwipm.ucanr.edu/agriculture/avocado/Anthracnose/
  11. https://link.springer.com/content/pdf/10.1007%2F978-3-319-06904-3.pdf
  12. https://coststudyfiles.ucdavis.edu/uploads/cs_public/b4/3d/b43d58d9-1e91-4a3e-80f9-a2edb14958b0/2020avocadohighdensitysandiegocounty.pdf
  13. http://www.avocadosource.com/CAS_Yearbooks/CAS_43_1959/CAS_1959_PG_75-78.pdf
  14. https://wwwipm.ucanr.edu/agriculture/avocado/SpecialWeedProblems/
  15. https://www.elgo.gr/images/ioanna/periodiko/Teyxos_22/AVOCADO.PDF

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

Yield, Harvest, and Post-Harvest handling of Avocado

The harvest, storage, packaging, and transportation of avocados are the most important processes of the food value chain and greatly affect the quality of the product.

Avocado yield per hectare and acre

The yield of an avocado tree depends on the following:

  • Age of the tree
  • Variety
  • Environmental conditions
  • Plant vigor and health (successful plant protection, fertilization, and irrigation)

An avocado tree starts producing fruits 3-4 years after planting, but the farmer will begin having economic gain after the 6th year. Depending on the year, my avocado trees (25 years old) produce an average of 70 to 80 kg (154 to 176 lbs.) of fruits per tree. However, based on international references, the yield of a mature tree per year may vary from 45 to 320 kg (100-700 lbs.) or 7-13 tonnes per hectare (6245 to 11598 lbs. per acre) (12). The size of the fruit is an important quality characteristic. Avocadoes are commercially acceptable when they weigh between 150 and 500 grams (0.33-1.1 pounds), but 400 g (0.88 pounds) is ideal. To achieve this, farmers need to perform all agricultural practices necessary to balance the amount and the size of the fruits produced on a tree.

In my fields in Crete, Greece (Mediterranean climate), I grow Zutano, Fuerte, and Hass avocado trees, with Zutano being the most productive among the 3 of them, followed by Hass and Fuerte. However, Hass may exhibit alternate bearing (more production in one year and less during the next). The phenomenon is stronger in trees that do not get pruned. By checking testimonials from other avocado growing areas with similar climates, like California, we saw that our yield areas are similar, with experienced growers mentioning that Hass can yield 8-13 tonnes per hectare (t/ha) (7137 – 11598 lbs. per acre) and Fuerte 7-11 t/ha (6245 to 9813 lbs. per acre) (3). However, if all conditions are favorable and the growers use suitable rootstocks, successfully control root rot, and apply irrigation and fertilization, they can achieve yields of even 20-23 tons per hectare (17843 to 20520 lbs. per acre) (24). Keep in mind that the yield per hectare or acre is affected not only by the production per tree but also by the plant density and the number of trees per hectare.

Harvesting time and method

Depending on the variety, the moment and duration of harvesting differ and are generally relatively fixed over the years. At the end of October (mid-autumn), we start picking the Zutano fruits. Due to their high sensitivity, harvesting needs to be completed very fast and carefully in order to maintain their good quality. The short period of time that the mature fruit remains attached to the tree and the early harvest seems to have a very positive impact on the amount of the yield. This way, the trees have a more extended period to “rest” and relocate all the nutrients and boost flower bud differentiation (next season’s production).

The situation is very different for Fuerte trees harvested right after the Zutano. In this case, harvesting can start from the beginning of November (start of winter) and lasts until May (end of spring). As you see, the “harvesting window” is very extended, allowing a steady supply to the market. However, at the same time, that means that we need to enter our field multiple times, something that many of my fellow avocado growers do not like because it costs a lot of money. Finally, we harvest the “summer avocado,” the Hass, during June and July.

While the harvesting moment has remained relatively stable over the years, a farmer needs to be able to detect the “right” moment to achieve the best quality and longer shelf-life. Avocado has a high rate of post-harvest respiration and is classified as climacteric fruit. This means that it has a relatively short shelf-life and continues to ripe even after harvest. However, if the fruit is harvested before it is mature, there is a high risk that it will shrink, have a bitter taste, and have a very firm-unpleasant texture.

Since Avocados do not soften on the trees, it is not easy to identify the right harvesting period. Some indicators and methods to determine avocado maturity include:

  • Optical observations:The change of color of the pile:
  • in dark varieties like Hass from green to black-purple
  • in green varieties, the fruit stem turns yellow, and the skin may appear less shiny (powdery appearance) with rust-like spots
  • By harvesting a few fruits and storing them at room temperature for 7-10 days. If they soften without shriveling and taste as expected, the fruit is ready for harvesting. We use this technique for Zutano and Fuerte that keep their green color even when they mature.

 

  • Dry matter test

Fruit of all cultivars must reach a minimum of 21% dry matter (4). This number differs between varieties. For example, Hass should be harvested when the dry matter content of the fruit is at least 23%. The Australian Agriculture and Food department suggest the use of the following formula to calculate dry matter content (5):

weight of the dried avocado sample (less weight of the container), multiplied by 100, divided by the weight of the fresh avocado sample (less weight of the container).

Calculation example:

Weight of fresh avocado sample (less weight of the container) = 125g (0.27 pounds)

Weight of dried avocado sample (less weight of the container) = 30g (0.06 pounds)

30g multiplied by 100 divided by 125g

= 24% dry matter

It is highly advised to harvest the fruits as soon as they reach these minimum levels because there is also an upper level of dry matter (maturity), after which palatability drops significantly.

 

  • Oil and fatty acid content measuring

The minimum oil content of 8% is necessary for marketing avocados (Ozdemir et al., 2004).

Finally, the farmer should follow the following principles:

  1. Harvest only during dry conditions.
  2. Pick the fruits from diseased trees last to minimize pathogen movement in the field and keep them separately from the healthy ones in storage.
  3. Harvest as soon as the fruit matures to reduce the damage caused by trips.
  4. Leave 0.5 cm of stem attached to the fruit.
  5. Take all prevention and control measures to decreaseanthracnose infection in the fruits.
  6. If there is a great fluctuation in the size and maturity level of the fruits in the tree or the orchard, start by picking the largest (more ripe) fruits first.
  7. Avoid picking the fruits from the ground or/and fit the trees with sticks to make the avocado drop.
  8. Use cotton gloves in order to protect the fruits.

On the larger orchards, trees are harvested with hydraulic ladders (cherry pickers), while on the smaller properties picking poles are used to reach the fruit from the ground. Fruit is picked into large bins, usually mounted on trailers. It is essential to keep the fruit out of direct sunlight after harvest to prevent it from heating (4).

Post-harvest handling

The maturity level at the moment of harvest and the environmental conditions affect the storage life of the avocado fruits. For example, the fruit can be consumed 20 days after picking from the tree in early harvesting during winter, while this period decreases to 7-8 days during summer. While I don’t do it myself, many farmers apply pre-cooling treatment to their fruits. This should happen within 5 hours from the harvest, followed by storing them at 5oC (41 oF). In other cases, a hot-water treatment can be applied to sanitize the fruits (immerse in 30oC (86 oF) water for 3-5 min) (1). This can help in the post-harvest control of anthracnose.

Soon after harvesting, we focus on cleaning, shorting, and grading the fruits based on their size and health-quality status. This procedure is very important since the avocado is marketed in 4 kilos boxes that can usually fit 12, 14, or 16 fruits, which will define the final price. Based on data from other countries, there are more size categories with the 4-kilo cartoons to fit from 4 (781-1,222 g or 1.7-2.7 pounds each) to 22 avocados (171-190 g or 0.37-0.4 pounds each). Avocados are exclusively packed in cartons made of solid or corrugated fibreboard. Plastic should be generally  avoided.

The fruits can be stored for 3-5 weeks at a temperature of 4-5 oC (39-41 oF) and relative humidity of 85-95%. It is very important to avoid any temperature fluctuations within the storing area or/and from and during transportation because it can decrease the quality of the product. We see this problem, especially in avocados imported from abroad. Finally, the farmer can use insulated or refrigerated trucks (6) for transportation.

References

  1. https://www.kalro.org/sites/default/files/avocadoproductioncultivation.pdf
  2. https://www.daf.qld.gov.au/businesspriorities/agriculture/plants/fruitvegetable/fruitvegetablecrops/avocado/harvestingavocados
  3. https://www.avocadosource.com/Journals/SAAGA/SAAGA_1991/SAAGA_1991_PG_15-18.pdf
  4. https://www.fao.org/3/x6902e/x6902e.pdf
  5. https://www.agric.wa.gov.au/avocados/avocadomaturitytestingusingdrymatter
  6. https://www.jica.go.jp/project/english/kenya/015/materials/c8h0vm0000f7o8cjatt/materialspdf

Ozdemir, F., & Topuz, A. (2004). Changes in dry matter, oil content and fatty acids composition of avocado during harvesting time and post-harvesting ripening period. Food Chemistry86(1), 79-83.

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

How to train a young Avocado Tree

Like many other fruit-bearing trees, avocados need to be trained to obtain a desirable shape/structure and size that will maximize production, balance yield and quality, and facilitate its cultivation. Before any action is taken, as a farmer myself, I would recommend that you take one step back and consider the needs and peculiarities of your field. Factors like the position of the field, the direction of the planting rows (wind exposure), the soil depth and fertility, the irrigation system, as well as the variety cultivated, the plant spacing, and the available means for harvesting should be taken into account when forming the permanent structure of the limbs. 

Training should start already from the first years of the orchard establishment. This is especially important when training for the central-leader system. If the trees are grown in a field with a slope, it is best to keep them shorter. This should also be done when the field has shallow soil or a very high water horizon. 

There are three main growing systems for avocado:

https://www.seeka.co.nz/vdb/document/398

Usually, avocado growers choose the “spreading” system. In this case, one of the training priorities is to create one strong tree trunk that can withstand the future weight of a mature tree and a high yield. The main branches should start about 70 cm from the ground. 

Branches that have more than half the thickness of the central shoot (future trunk) must be removed (2). Around four strong branches are also selected to be the primary limbs. Generally, avocado is irrigated with drip irrigation systems. However, some farmers choose to install and use sprinklers. In this case, it is essential to have one single, clean trunk, with the branches starting a bit higher, so they do not interfere with the water distribution. 

To facilitate harvesting from the ground, avocado farmers want to promote lateral growth of the trees. The farmer should take all necessary actions to encourage lateral growth and multiple framework branching. Terminal shoots should be pinched at the beginning of the second growing season. These should be repeated until the trees have obtained the desired structure and height (3). 

However, I have witnessed many cases where the grower did not have the available space due to close planting distances and, to avoid losing any yield, allowed the vertical growth of the trees. The result was that the trees became very tall, the fruits were developing in the upper 2/3 of the tree, and the use of specialized machinery and ladders was necessary for harvesting (4). I highly advise any farmer to avoid such practice and consider the final size of the trees when planting their avocado orchard. Fruit picking may be facilitated by forming a tree with a low vase type of head. However, such “open” formation should be avoided in areas exposed to strong winds because limbs can break. 

Young trees need all the nutrients and water they can get to maintain their quick-growing rhythm. As a result, the farmer must often remove all suckers growing from the tree basis. Similarly, all branches grown below the graft or bud union should be removed if the avocado is grafted. 

You may avoid pruning young avocado trees very strictly (excessively) since this will delay the production phase even more. Finally, after the first three years of training, the farmer should not neglect its trees and perform pruning annually. 

Pruning avocado trees: A simple procedure that should not be neglected

Generally, avocado trees do not need too much pruning after the 4th year of growth in the field. However, some pruning is vital for a high and stable avocado yield over the years since it gives control of flowering (productive) wood (1). It can influence the amount and quality of fruit production and maintain the height and formation of the trees. Generally, avocado trees tend to become tall, and if this tendency is not under control, cultivation activities like harvesting will become very difficult in the years to come. As a result, I trim the tops of the branches every two years to keep my avocado trees at a maximum height of 10 m (32.8 ft). This happens after harvest. 

Before starting, you should walk around the tree and observe its canopy. Then you may come closer to the trunk, put your back against it and observe the interior of the canopy. This will reveal to you all the necessary parts that need to be cut. 

The principles to keep in mind when pruning an avocado tree are the following:

  • Remove all suckers that grow from the tree’s base and rootstock. 
  • Any intervention should be applied only when the tree is dormant and before the flowering buds start developing. Too late pruning (late in the spring) can result in nutrient loss and exposure of the sensitive new vegetation to the sun (sunburns are expected). On the other hand, pruning too early (end of summer) may lead to frost damage to the newly developed branches during the winter (4). 
  • Prune dead and infected wood to reduce the spread of the infection to healthy plant parts during the following season. 
  • Try to keep a more open formation with branches of lateral growth. Remove any branches that go downwards, inwards, or pinch out the terminal buds of or the branches that grow straight up. Trim the branches by 1/3 or 1/4 of their size.  
  • If a vigorous secondary limb is shading or leads a primary lateral down, it should be (partially) removed (5).
  • Avoid pruning the tree too heavily because it will lead to excessive leaf loss and favor vegetative growth against fruit formation. 
  • You can open “windows” to improve aeration and sun penetration that will help flowering and fruit set. In regions with very high solar radiation and heatwaves, it is better to leave enough vegetation to offer shade and protect the branches, the trunk, and the fruits from sunburns. 
  • It is better to thin the number of branches in order to maintain a 30-38 cm (12-15 in) distance between them. This will allow enough light to enter the tree canopy and simultaneously reduce the friction and bumps between branches when strong winds prevail).
  • Rejuvenate the branches to keep them productive (new fruit-bearing wood). Depending on the variety, you may need to remove one major limb per year (6). 
  • Fruit thinning is not necessary for avocados, in my opinion. 

Except for the training (formation pruning) and the annual pruning, there might be a need to perform regenerative pruning in very old trees where productivity has declined. Additionally, in high-density orchards, growers often choose to remove trees after seven years, to allow the growth of the remainings (1). In every case, the farmer should consult a local agronomist and find the more suitable strategy and pruning method that matches his/her variety, field, goals, and local environmental conditions.

References

  1. https://www.seeka.co.nz/vdb/document/398
  2. https://www.avocadosource.com/Journals/SAAGA/SAAGA_1996/SAAGA_1996_PG_73-76.pdf
  3. https://www.jica.go.jp/project/english/kenya/015/materials/c8h0vm0000f7o8cj-att/materials_02.pdf
  4. http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/avocadotraining.html
  5. http://www.avocadosource.com/CAS_Yearbooks/CAS_20_1935/CAS_1935_PG_098-103.pdf
  6. https://www.daf.qld.gov.au/business-priorities/agriculture/plants/fruit-vegetable/fruit-vegetable-crops/avocado/planting-and-growing-avocados

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

 

Fertilization in Avocado Farming

To keep the avocado tree vigorous, healthy, and productive, the farmer in soce cases may need to cover the crop’s nutrient needs via fertilization. From my experience, avocados do not have a very high demand or great response to fertilizer application in the average soil with no particular deficiencies. However, it is crucial to avoid any nutrient deficiencies and provide the proper nutrients in the amounts needed and at the best time (highest demand from the tree).

Before planting our orchard, we should always perform a soil analysis that will give more information concerning, among others, the soil characteristics (which can affect nutrient availability) and the nutrient reserve. If the trees have already been planted, it is best to simultaneously perform the sampling for soil and leaf analysis (end of the spring/start of winter) and interpret the results together.

To form a specialized fertilization program for avocado trees, we also need to know the type and amount of nutrients removed yearly from our field (e.g., due to harvesting or pruning) and the plant nutrient demand to perform specific processes during the growth cycle, such as flowering.

While nitrogen is the most important since it has a vital role in (shoot) growth and development of the avocado trees, the rest of the nutrients have a critical role. More specifically, Phosphorous is needed for healthy metabolism, Potassium and Zinc are needed for a healthy fruit, Calcium is needed for root growth and fruit quality, Magnesium is needed for improved photosynthesis capacity, and Boron is needed for flowering and fruit set, while Iron and Manganese are also important for plant’s health (1).

More specifically, a yield of 2.7 tonnes (6,000 lbs) can remove approximately 7 kg (16.8 lb) nitrogen (N), (14.6 lb) Phosphorus (P2O5), 18-22 kg (40-48 lb) K2O and more than 2.7 kg (6 lb) of Calcium, Magnesium, Sulfur, and Sodium from the soil (2).

Designing the fertilization program for avocado trees

In rainfed avocado orchards, growers mainly spread the granular fertilizers around the canopy projection before and or/ right after the rainy season (spring). At the same time, in fields with drip irrigation, fertigation is preferred due to the higher precision and efficacy. My avocados grow under irrigation in Crete, Greece, and I choose to fertigate. Fertigation means fertilization and irrigation simultaneously, that is, injection of water-soluble fertilizers in the irrigation system.

To cover the needs of my mature (25 years old) trees (Hass, Zutano, and Fuerte), I use 2 compound fertilizers and apply 1-4 kg per tree annually, broken down into two applications. More specifically, I apply through the drip irrigation system a 20-20-20 (N-P-K) fertilizer in December (mid-winter) and an 18-8-14 (N (NH4NO3)-Κ-Β) in August (end of summer). However, farmers should keep in mind that the actual amounts needed can change with the amount of production and of course the age of the avocado tree.

Type and amount of nutrients needed from young to mature avocado trees

Depending on the soil fertility, the farmer may need to add animal manure six months before planting. Topsoil is mixed with 20 kg per hole of well-decomposed manure and 0.25 kg (0.55 lb) of either Triple Super Phosphate or rock phosphate in the planting hole before refilling (3).

You must avoid any application very close to the planting (before or after) to protect the sensitive young root system from “burning.” Young (non-bearing) trees are usually fertilized every 3 to 6 weeks throughout the growing season (from early spring until early autumn). The amount that can be applied to 1-year-old avocado trees annually are:

  • 045 kg (0.1 lbs) N or 0.15 kg (0.33 lbs) LAN fertilizer (28% N),
  • 021 kg P (0-0.046 lbs) or 0.2 kg (0.44 lbs) Superphosphate (11.3% P), and
  • 075 kg (0.16 lbs) K or 0.19 kg (0.42 lbs) K2SO4 (40% K) (4).

The doses of fertilizers may double in the second year for all nutrients, while other nutrients such as Zinc (Zn) are added. P and K are more important in later growth stages (older trees). For example, as we mentioned above, K is needed in fruits. As a result, in non-productive young trees, the farmer should only include K in the fertilization program when the leaf K range is less than 0.85% by adding 11-45 kg of K2O per hectare (10-40 lb per acre) (5).

The doses of fertilizers will increase until the 12th year of the plant’s life, and from that point onwards, they will remain relatively stable for the following years. Generally, 0.5 – 0.8 kg (1 – 1.8 lbs) actual N, 0.19 kg (0.42 lbs.) P, and 0.75 kg (1.65 lbs) K per mature tree per year may be needed for a good yield. If the farmer wants to use synthetic fertilizer, he/she should choose a product with 1:1:1 or 2:2:1 (N: P: K) proportion (6). Moreover, up to 56 kg per hectare (50 lbs per acre) of Zn may be needed in spring or early summer to correct a nutrient deficiency.

Different varieties have their own nitrogen needs. For example, in leaves of Fuerte, a nitrogen level above 2.0% is associated with reduced yield, whereas in Hass, the same or higher (up to 2.9%) amount is considered ideal (7).

Type of fertilizers and time of application during the season

Avocado trees take up most of their nutrients between full bloom and autumn and during the following spring.

Most of N is taken up by the roots as nitrate (NO3‐) and less as ammonium (NH4+) (2). The application of urea in avocado orchards is not recommended due to the low uptake ability of the trees. In general, N fertilization is performed from the soil. Still, some references mention that N (urea) foliar spraying to flowers and young leaves has the potential to increase yields and fruit size (5).

Mid to end summer has been suggested as the more appropriate period for applying P and K fertilization, which can boost the growth of the current year and the initiation of next spring’s inflorescences (5). The most commonly used fertilizer types for fertigation using P are Phosphoric acid. K Potassium sulfate, potassium thiosulfate, and potassium nitrate are widely used. It is advised to avoid applying P and Zn fertilizers together with fertigation or using calcium or using phosphoric acid when the irrigation water is rich in magnesium phosphates, since they can chemically react and clog the irrigation system. Foliar applications of K are not so efficient, while for P, scientists have found some positive results in the “off” years (less yield).

Finally, to improve the fruit quality, the farmer can add calcium (Ca) during the first 6 – 8 weeks of fruit growth (8). This can be performed either with:

  • foliar application – Ca(NO3)2 at a rate of 100-300 kg/ha split into 2-4 applications, with
  • soil application (Gypsum (Ca + S) at a rate of 1-3 tons/ha broadcasted) or
  • through fertigation (Buffered Ca (170 g / L, 17 % Ca) can be applied post fruit set at a rate of 7.5 L/ha every 7 – 14 days until harvest) (4).

Lime or dolomite can be added if needed (after soil analysis) once every 2–3 years in very acidic soils to raise the pH and supply the plants with calcium and magnesium. The maximum amount per application is 2 t/ha. If more is needed, you need to split the applications in smaller doses (9).

However, these are just common patterns that should not be followed without doing your own research. Every field is different and has different needs. It is highly recommended to examine the soil and leaf analysis results carefully and consult your local licensed agronomist before applying any fertilization method.

References

  1. https://www.californiaavocadogrowers.com/sites/default/files/Californiaavocadofertilizerbestpractices.pdf
  2. http://www.avocadosource.com/papers/research_articles/crowleydavidpdf
  3. https://www.jica.go.jp/project/english/kenya/015/materials/c8h0vm0000f7o8cjatt/materialspdf
  4. http://redsunhort.co.za/wpcontent/uploads/DOWNLOADS/Avogeneralnormsandfertigationguidelines.pdf
  5. https://www.cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/Avocado.html
  6. https://www.fao.org/3/X6902E/x6902ehtm
  7. https://ucanr.edu/sites/alternativefruits/files/121293.pdf
  8. https://www.californiaavocadogrowers.com/culturalmanagementlibrary/avocadotreefertilizationbasics
  9. https://www.daf.qld.gov.au/businesspriorities/agriculture/plants/fruitvegetable/fruitvegetablecrops/avocado/plantingandgrowingavocados

 

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

Avocado Water Requirements

A sufficient and well-distributed water supply is vital for a healthy avocado orchard that can offer sustainably high yields for many years. Since avocado is native to the humid subtropical and tropical regions with abundant rainfall, crop cultivation in different climatic zones and environmental conditions may need extra irrigation to cover the plant’s water requirements.

After transplanting, the farmer can create a basin around each tree to collect water from rain or irrigation. The grower can regularly water the newly planted avocado trees until they are established. The amount and frequency of irrigation will change as the trees mature.

In my fields in Crete (Greece), winter rainfalls are sufficient to cover the water needs of avocado trees during that period. However, during summer, I apply irrigation through drippers once every ten days, for 1-2 hours. While this practice is efficient for my orchards, I advise other avocado growers to form specialized irrigation schedules for their fields.  

How much water does an avocado tree need?

Avocado is considered a water-intensive crop. The exact amounts of water needed depend on the environmental conditions, the soil characteristics, and the age of the trees. Generally, a mature tree needs at least 1,000-1,300 mm (40-50 in) of rain per year (1). In Mediterranean climates, a single tree may require up to 51 mm (2 in) of water per week during the dry and warm summer months. More specifically, based on scientific data, in hot climates, avocado water use is around 45 liters per day (l/day) in spring, 136 to 220 l/day during summer, and 121 l/day in autumn (23). The avocado tree has shallow roots that are spread mainly in the top 20-60 cm of soil and are not very efficient in exploiting water from deeper soil layers. As a result, rainfalls and/or irrigation should keep the soil’s upper 15-20 cm (6-7 in) moist (4).

These amounts should be delivered to the plants in smaller quantities with more frequent irrigation sessions. However, the farmer should know that too frequent light irrigation may encourage shallow root system growth, making the plant less tolerant to drought and strong winds. Flooding is not desirable as it promotes root rot as well as water and nutrient runoff and should always be avoided, in my opinion.

When and how to irrigate an avocado tree? 

Avocado trees have large soft leaves and evaporate a lot of water in warm weather, so they need regular watering (5). The most critical periods are the flowering and fruit set. During these growth stages, the farmer should interfere with irrigation if the rainfalls are insufficient to reduce fruit drop and increase the final fruit size (3).  

For determining the frequency of irrigation sessions, the farmer should take into account the:

  • Local and seasonal environmental conditions. In areas with long, dry, and warm summers, irrigation may be needed every 7-10 days during summer. While, in most cases, winter rainfalls can cover the water plant needs, it is best to irrigate if there are long dry spells and the soil has dried out. Many farmers use mulching (green manure) as soil cover to preserve the soil moisture.
  • soil characteristics (e.g., more frequent irrigations with fewer water quantities in sandy soils)
  • the acceptable stress level that the trees will experience
  • availability of water

Best irrigation systems for avocado trees

The main two irrigation systems used successfully in avocado farming are drip irrigation and low-volume sprinklers. You may irrigate your trees using a drip system with either two to four emitters per tree or small micro-spray emitters (2). To have the best results, it is advised to place the drippers on the ground close to the active root systems (at the limits-projection of the canopy). As the tree grows, remember to change the position of the drippers as well. In orchards where a drip irrigation system is used, the farmers can choose to fertilize their trees using fertigation (= fertilization + irrigation, i.e., water-soluble fertilizers injected into the irrigation system). If you choose this system, you may prefer a single trunk training system for your trees, with a higher canopy that does not interfere with the water distribution. On the other hand, sprinkler irrigation has been reported to improve the fruit size and oil percentage (6).

Avocado trees are sensitive to high soil salinity. For this reason, irrigation water quality plays an important role. Water with less than 100 ppm of chloride salts is suitable for avocado farming (7). High iron concentration (more than 1 milligram per litre) in the water can also create significant problems for avocado growers. This is more common when using underground water resources (4).

As mentioned above, each field is different. To form a more suitable irrigation schedule, the farmer can use various instruments to assess the moisture level accurately and determine readily available water. Some cost-effective techniques include using simple technology like tensiometers or porous blocks that can help a grower decide when and how much to irrigate (8here).

References

  • https://www.californiaavocadogrowers.com/cultural-management-library/assess-avocado-grove-irrigation-methods

 

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

 

Avocado Tree Propagation

After selecting the desirable avocado variety to cultivate, the farmer needs to obtain the appropriate amount and type of reproduction material to plant. Avocados can be propagated by planting seeds, cuttings, grafting and layering. Usually, grafted seedlings are the more common propagation material used for commercial cultivation. Grafted seedlings offer the significant advantages of uniform and accelerated growth and higher yields, which is why we prefer them as a starting material in our orchards.  

Propagation of Avocado Trees Grafted on seedling rootstocks became a more common technique mainly after the root rot disease incited by Phytophthora became economically important. Moreover, the use of resistant rootstocks became handy in many other cases. For example, avocado is extremely sensitive to salinity (especially the Mexican race), alkaline conditions, lack of aeration (heavy soils), poorly drained soils, and lime-induced chlorosis. To overcome all these and grow popular but sensitive avocado cultivars in various soils and environments, most farmers prefer to use grafted plants on resistant rootstocks (1). 

Producing avocados from seeds usually takes place in the nursery, but there are cases a smallholder or an amateur farmer can perform it. For a higher success rate, the seeds that will be used must be collected from ripe, healthy fruits still attached to the trees. As a next step, the seeds should be properly stored (if you intend to plant them later) or treated in a water bath for 30 minutes (50oC or 122oF). After the treatment, the seeds need to be cooled down and dried. Different substrates (potting mixes) can be used to plant the avocado pit, such as mixes of 3 parts peat moss to 2 parts perlite or 1/3 peat, 1/3 perlite, and 1/3 vermiculite. We can remove the seed coat and place the seed with the apical end at the surface of the potting mix. If temperature and soil moisture are at appropriate levels, germination is expected within 4 weeks. Some of the most widely used varieties as seedlings belong to the Mexican race (Topa-Topa, Mexico, Mexicola). Keep in mind that the farmers must purchase this material from a certified plant nursery.

As mentioned before, the avocado trees will carry some specific characteristics depending on the race chosen to be used as rootstocks. On a large scale, the Mexican race is considered one of the most popular rootstocks used for cultivation in regions like California, Israel, and South Africa. West Indian stocks are preferred in warmer regions or where salinity is a problem. At the same time, the Guatemalan race is mainly used in warmer climates and field neutral pH and has no problems with Verticillium wilt (2). Nowadays, scientists concentrate their efforts on finding and breeding avocado varieties tolerant to climate change effects, like drought. These varieties will then be used as rootstocks to cultivate important commercial varieties across the globe.

Pollination of Avocado trees

Even in ideal conditions, from the million greenish-yellow flowers produced per plant, only a few are fertilized and will produce fruits. Even though avocado has perfect, bisexual flowers (that have both male and female organs), the self-fertilization is not sufficient to produce enough (or any) fruits. The reason behind this “malfunction” is the unique flowering behavior of the avocado trees, known as “protogynous dichogamy,” which leads to categorizing all varieties into 2 group-types, based on the moment that the flowers will become reproductively functional as males or females. In this scheme, self-fertilization happens during the second opening of the flowers within the day. However, usually, cross-pollination is needed to increase fruit production (3). 

https://www.agric.wa.gov.au/spring/cross-pollinisers-hass-avocado

To manage that, we selected to cultivate in the same field two varieties of avocado, one from each type. This allows us to have an overlapping flowering of mature male and female flowers from type A and B plants and successful fertilization. We use Hass as a “pollinizer” variety since we cultivate two type B varieties (Fuerte and Zutano) and one type A variety (Hass). By placing two Hass trees every 20 plants of the type B varieties, we have seen that we gain the desired result. The “pollinizer” are usually placed at key spots to benefit from the wind drift. While it is generally advised to have a 1:1 or 1:2 proportion of the plants of different types, our plants give medium to high yield. We speculate that the main reason for this is the small size of our fields (2-3 stremmata, 0.2-0.3 hectares) and the neighboring with other avocado fields. 

The classification of the most important commercial varieties into the two types can be seen in the following table. 

“A type” varieties“B type” varieties
HassFuerte
GwenZutano
LambBacon
PinkertonEttinger
ReedSharwil
GEMSir Prize
HarvestWalter Hole
WurtzEdranol
RinconNabal
AnaheimNobel
BenicBooth3,5,7,8
DickinsonAbobodo Mabal
DukePollock
Mexican August
Yama

 

However, there are also some exceptions with varieties such as “Waldin,” “Lula,” and “Taylor” that fruit well when planted alone, since self fertilization happens at a good level. Finally, scientists suggests that since avocado is mainly pollinated by bees, the farmer can introduce some beehives to his/her field during the flowering period (43). At least 10 bees per tree are needed (6). Cross-pollination works better in temperatures around 20-24 oC (68-75 oF), while avocado fruit set is favored at 18-24 oC (65-75 oF) . 

High temperatures (over 38-40 oC) or/and strong warm winds during flowering are the main problem that most farmers experience and can cost them their production (yield decrease up to 70%). Extended problems and yield losses due to heat can occur in the fruit developing stage. Young fruits are more sensitive, and their temperature can increase dramatically. In this case, they become soft and they are no longer viable. Some research results mention that there is a risk of quality deterioration under such conditions since the composition of the various oils in the avocado can be affected (5).  We advise the farmer to leave sufficient leaf area after the yearly pruning to protect the fruits from sunburn. Together with some other farmers, we have obtained some good results by applying Zinc Chelate products to our plants during flowering, when the temperature is dangerously high (summer period). 

References

  1. http://www.avocadosource.com/journals/horticulturalreviews/hortrev_1995_pg_381-429.pdf
  2. https://www.fao.org/3/X6902E/x6902e06.htm
  3. https://www.kalro.org/sites/default/files/avocado-production-cultivation.pdf
  4. https://www.agric.wa.gov.au/spring/growing-avocados-flowering-pollination-and-fruit-set
  5. https://www.californiaavocadogrowers.com/cultural-management-library/managing-avocado-heat-damage
  6. https://www.californiaavocadogrowers.com/cultural-management-library/spring-pollination-avocado-groves

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

 

Avocado Tree Climate and Soil Requirements

My orchards (3 hectares) are located in different fields in the Chania region of Crete. The ample sunlight, the warm climate, and the amount of winter rainfalls compose an ideal microclimate for avocado cultivation and the production of high yields. All three varieties that I have planted (Hass, Zutano, and Fuerte) seem to be perfectly adapted to the local conditions.

Soil and location

Avocado trees can grow well in a wide range of soils. The ideal soil for most varieties is loose, loamy, or sandy with a slightly acidic to neutral pH, between 5 and 7 (1). However, farmers should generally avoid establishing an avocado orchard in fields with poor drainage and high salinity. West Indian varieties are generally the most salt-tolerant and are preferred for plantations in coastal regions. The cultivation is possible at elevations from sea level to 2,400m (7,874 ft). Additionally, avocados should be planted in fields with a maximum slope of 15% and areas protected from strong winds. Avocados have a high water demand, and if the rainfalls are not sufficient (annual precipitation of 800–1700 mm) or well spread during the season, there might be a need for irrigation to support high yields (2).

Temperature and sunlight

The sudden temperature changes can stress the avocado tree. Frost is usually not an issue in our region, but the low temperature is one of the most limiting factors for growing this tropical species in other areas. As a tropical crop, avocado can survive temperatures between -4oC and 40oC. However, the level of the damage depends on the duration of these extreme temperatures and the variety. For example, Hass, like most varieties, thrives in an average temperature of 16 – 21 oC (60-70 oF). While young trees (up to 3-5 years) are generally sensitive to low temperatures, mature trees can withstand temperatures as low as -2 oC (28 oF). In order to produce flowers, avocado needs at least four weeks during autumn-winter with cool temperatures. However, during blooming, the temperature should remain above 10oC.

On the other hand, high temperatures can also harm the trees and their production. Temperatures over 40oC can cause severe damage to sensitive young trees and stress the older ones. Most severe problems are recorded during the end of summer when heat waves and warm winds are most common. During this period, avocado trees are in the most sensitive phase since they bloom or form fruits. Such conditions can lead to flower necrosis, fruit drop, and as a result, a significant yield loss. Unfortunately, I have personally witnessed such issues, and the continuous increase in temperature due to climate change worries all the avocado producers in the region. To help our plants during these events, we irrigate and apply Zinc Chelate and zeolite products during flowering. In other areas, farmers use overhead sprinklers for evaporative cooling to preserve the crop (3).

Finally, most avocado varieties need 6-8 hours of ample sunlight daily. The sun will help maintain the bright green color of the leaves and the fruits. In mature trees, sunburns are not very common. However, young avocado trees must be protected. Intercropping with larger trees, painting the trunks, and using shading nets can help.

Use of shading net to protect the young avocado trees from sunburns (7)

Keep in mind that the environmental requirements significantly differ among the avocado varieties. A farmer should examine his/her field, list the limiting factors and select the most adaptive avocado variety.

Planting an avocado orchard – Number of Avocado trees per hectare

After a farmer has selected and purchased the seedlings of an appropriate avocado variety and the field location, the establishment of the orchard is quite simple. Start by clearing the field of weeds since strong competition with the young avocados for nutrients and water may negatively affect their growth. It is generally recommended in colder areas to plant the young trees at the start of fall, while in warmer regions, the mid-end of spring is the most suitable period. This way, the plants will have time to establish and adjust before the extreme temperatures.

Avocado plant distances may vary between 6 to 12 meters depending on the desirable plant density we want to have and the variety we have selected. For example, a wider spacing should be given for varieties with a spreading type of growth, like Fuerte. The most common planting distances are 7 X 7m (23 X 23 ft.), 10 X 5m (33 X 16,5 ft.) , or 6 X 3m (20 X 10 ft.). That will result in a plant density per hectare of 200 trees, or more than 500 trees, respectively (3). In our fields, I selected to plant at a 6 X 6 m scheme (20 X 20 ft.). Ideally, I would prefer 3 X 6m or 3 X 5m distances, but when I planted the trees, there were also orange trees in the field.

It is quite a common strategy to incorporate some manure or compost in the soil before planting in order to offer the necessary nutrients to the young seedling during the first year. The avocado tree is transplanted with the soil ball. The planting hole should be approximately three times wider than the plant container and two times deeper (around 0.6-1m or 2-3 ft). Attention is needed because the roots are sensitive (especially in Hass).

During the first years, the orange trees protected the young avocado from the strong winds and intense sunlight. However, 3 to 4 years later, I decided to remove the orange trees as the avocado plants became bigger. Intercropping or mixed cropping systems with avocado are quite popular in many regions globally. The most commonly used tree -“partners” are orange or citrus trees, coffee trees or even olive trees (4, 1). Alternatively, the farmer can plant annual crops like potatoes, beans, peas, kale, or cabbage during the first 3-5 years between the tree rows to gain some profit until the avocado trees start producing fruits (5).

Attention: Keep in mind that you need to include a “pollinator” variety (of the opposite type, A or B) in a proportion of 1:1, 1:2, or 1:5.

References

  1. https://www.fao.org/3/X6902E/x6902ehtm
  2. https://link.springer.com/content/pdf/10.1007%2F978-3-319-06904-3.pdf
  3. https://www.daf.qld.gov.au/businesspriorities/agriculture/plants/fruitvegetable/fruitvegetablecrops/avocado/plantingandgrowingavocados
  4. http://livingagro.maich.gr/
  5. https://www.kalro.org/sites/default/files/avocadoproductioncultivation.pdf

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

The rising interest of consumers for avocado has skyrocketed the global demand for this fruit, and as a result, new areas are planted with avocado every year.

I planted my orchards 25 years ago in different fields (in 15 different locations) in the Chania region in Crete (Greece), where the microclimate is highly favorable for growing avocados. I selected to cultivate Zutano, Fuerte, and Hass due to their excellent adaptation to local conditions and the medium to high yields. As a farmer, I prefer Zutano because it can offer the highest yields.

As a trader (and exporter) myself, I prefer Fuerte for its better storability and prolonged harvesting period. The fruits can be harvested from the trees from November until May in Crete, allowing a more consistent market supply. Fuerte is also the number one choice of Greek consumers. On the other hand, Hass is the most popular among European consumers due to the higher quality and better taste of its fruits. As a result, all production of Hass avocados is exported.

Advice

I advise fellow farmers to cultivate more than one variety with different maturity times in order to spread the risk of losses and the workload during harvest. Since the plants start producing fruits after 3-4 years from their planting, the farmer needs to take into account many factors to make an informed choice regarding the avocado variety selection. Ideally, he/she can plant some “test” trees from different varieties to see their response to the local conditions.

What to consider when selecting an avocado variety

All varieties are classified into three horticultural races: the West Indian (Persea americana Miller var. americana), Guatemalan (Persea nubigena L. Wins var. guatemalensis), and Mexican (Persea americana Miller var. drymifolia Schlecht and Cham). However, a large number of commercially interesting varieties are hybrids.

Some of the most important avocado hybrids are the result of crosses between:

  • Mexican x Guatemalan varieties: Ettinger, Pinkerton, Fuerte, Bacon and
  • Guatemalan X West Indian varieties: Choquette, Beta, Lula, Semil 34, Monroe
  • Inter-race crosses are also possible: Reed, for example, is the result of the cross between 2 Guatemalan avocados à Anaheim X Nepal.

The choice should be made by considering the following:

  • The environmental conditions of the area where the trees will be planted. Many varieties in the market can perform well in climatic conditions ranging from true tropical to warmer parts of the temperate zone. If the main limiting factor in the area of interest is the temperature, you should try to find a relatively tolerant variety. Avocados are generally sensitive to extreme temperatures and do not react well to fluctuations or abrupt changes.

The varieties that are tolerant to lower temperatures are described as “cold-hardy” avocados. These varieties usually can withstand temperatures ranging from -1oC-4.4oC (30-40oF). Among the most popular varieties, the following seem to have some degree of cold tolerance: Bacon, Duke, Puebla, Lula, Reed, Mexicola, Taylor, Tonnage, Choquette, Fuerte, Ryan, Stewart, Zutano, and Sharwill. In general, avocado varieties of the Mexican race are the most cold-tolerant. As a result, Mexican rootstocks are preferred to be used for grafted seedlings in colder areas. However, avocado farmer should not choose them if their field has salinity problems. West Indian avocados are the most sensitive to low temperatures (1).

Varieties that belong to the West Indian race are suitable for warm tropical climates. They are widely cultivated in different areas of India (Maharashtra, Tamil Nadu, and Karnataka) and the lowlands of Tropical America. In general, these varieties have been reported to be more heat tolerant. Some of them are Fuchsia (Fuchs), Simmonds, and Waldin. Despite its popularity, Fuerte is not the best option for cultivation in the tropics. A suitable alternative could be the hybrids of the race with Guatemalan varieties (see above). However, the Mexicola variety is well adapted both in warm and cold conditions.

At the same time, avocado is generally sensitive to high salinity, drought, and saturated soils. In fields with known history, the farmer should choose a variety (or rootstock) with high tolerance to such limiting factors.

  • The market demand. This can reflect both the customers’ preferences for specific varieties and the seasonal demand for the product. Suppose the farmers want to export their product to other countries. In that case, they must also consider the preferences of the local consumers and, of course, the resistance of the fruits to transportation and more extended storage.

Quality characteristics and morphology of the most popular avocado varieties

  • Mexican race

In general, the varieties of the Mexican race produce small (250 g) fruits that ripen 6 to 8 months after flowering (end of fall-start of spring). The fruit has a thin green smooth skin that keeps its color even when ripe and the highest oil content (up to 30%). Especially in Mediterranean climates, one of the most popular varieties belonging to this race is Zutano.

Zutano

Zutano is characterized as a “season opener” since its harvesting period starts in early fall and can supply the market until early winter (2). It is a type-B variety and is preferred by the farmers due to its high and consistent yield and good cold tolerance. The fruit has a pear shape, is medium to large (0.168 to 0.400 kg), and has shiny, bright green skin. It is less rich, creamy, and tasty compared to many other avocado varieties. The tree can reach up to 12 m (40 feet) in height. The trees start to produce fruits at a young age (2-3 years from seed).

Other important varieties of the Mexican race (or crossed with it) are: Duke, Mexicola, (Ettinger, Pinkerton, Fuerte, and Bacon)

  • Guatemalan race

The varieties of the Guatemalan race are the most important and widely cultivated in California. The trees bloom in mid-late spring, and the fruits ripen and stay on the trees up to 9-12 months later. The fruits are relatively large, weigh up to 600 g, and have thick, warty skin. The oil content in fruits ranges between 8 and 15%.

Hass and Fuerte are the most widely used varieties of the Guatemalan race. However, both carry important genes (characteristics) of the Mexican race (Bender, 2012). Furthermore, these two varieties are usually combined in the same field since they offer a good level of cross-pollination. Despite their excellent characteristics, the farmer, before selecting them, needs to take into consideration that neither are very heat-resistant (1).

Fuerte

Fuerte is one of the most loved varieties for exports. It can survive low temperatures making it an important cold-hardy variety. The fruit has the shape of a pear (pyriform) and weighs between 200 and 400 g. It has a good quality and oil content (up to 26%) and is tastier than Zutano but less tastier compared to Hass. Like a “classical” Guatemalan race, Fuerte offers a large window for harvesting that can allow a consistent supply to the market, but depending on the size of the orchard could be time-consuming for the farmer. The trees become pretty large, requiring more space to grow compared to other varieties. Its sensitivity to anthracnose and scab may limit its cultivation in regions-fields with a known history (3). Regarding flowering, Fuerte blooms early in the season and is a type B variety.

Hass

The Hass variety of avocados is the most commercially interesting in the world, mainly due to its superior quality, taste, and long shelf-life. In the United States of America, the Hass variety accounts for 80% of the production, while in California, America, and Greece this percentage varies. Hass is predominantly Guatemalan but also has some Mexican genes (1). The trees can become very tall and require cutting back, while the canopy looks like an umbrella (3). For the North hemisphere, Hass has type A flowers and is characterized as a summer avocado, with the harvest to take place during June-August. The fruit has a medium size and an oval shape. One of the most distinctive characteristics of the variety is the change of the fruit’s skin color from green to dark purple when ripe and its hard, thick, and rough skin texture. Extra attention is needed because Hass is susceptible to Persea mites and thrips.

Other important varieties of the Guatemalan race (or crossed with it) are: Nabal, Taylor, Tonnage, Dickinson, (Ettinger, Pinkerton, Fuerte, Bacon, Choquette, Beta, Lula, Semil 34, and Monroe).

  • West Indian race

Finally, the West Indian race varieties are primarily cultivated in South America and Asia (India, Indonesia, etc.) and need warm climates to grow. The fruit is medium to large, varies in form, and the skin is usually smooth, leathery, and glossy. It has the lowest oil content compared to the fruits of the previous two groups. They bloom at the end of the fall-start of spring (February to May for the North hemisphere) and require 6-7 (sometimes up to 9 months) from flowering to ripe.

Some of the most popular varieties of this race are Booth, Waldin, Simmonds, and Fuchsia, while as a result of crosses with Guatemalan race varieties are the Choquette, Beta, Lula, Semil 34, Monroe.

References

  1. https://link.springer.com/content/pdf/10.1007%2F978-3-319-06904-3.pdf
  2. https://californiaavocado.com/avocado101/avocadovarieties/
  3. https://www.jica.go.jp/project/english/kenya/015/materials/c8h0vm0000f7o8cjatt/materialspdf

Bender GS (2012) Avocado production in California. A cultural handbook for growers, 2nd edn. Univ Calif Exp Program, Ch. 2 pp 1–32

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

Avocado originated from Puebla in South Central Mexico. The consumption of the fruit started around 10,000 years ago, and its domestication and cultivation around 5,000 years ago. During its long history, the avocado became known by different names. Some of them are “Fertility fruit,” “Alligator pear,” and “Butter fruit” (1). Until the 1950s, 25 varieties of avocado were commercially exploited, with the “Fuerte” being the most popular. This changed after 1970, when a new variety, “Hass,” took the lead in many avocado-grown countries and industries due to its superior taste and high oil content.

As the fruit became more popular, the cultivation of the tree expanded in new regions with tropical, semitropical and Mediterranean climates. Based on FAO data, Mexico comes first in production with more than 2,4 million tons yearly, followed by other Latin American countries, Indonesia, Kenya, and Israel.

Avocados became widely popular after 1980-2000, even in countries and continents that were never grown or consumed before. Avocado fruit has a dark green, knobby skin, buttery texture, and fresh, mild taste. As a fruit, it seems that it can be classified as a berry, and thanks to its high nutritional value, it is preferred by vegans and vegetarians. At the same time, avocado is a popular ingredient for culinary, as a spread, in salads, smoothies, and desserts.

The high content of the fruit in poly and mono-unsaturated fats (75% of total fats of the fruit) can help reduce blood cholesterol levels and decrease the risk for heart disease. At the same time, consumption of moderate amounts can provide humans with 20 vitamins and minerals, while it is sugar and sodium-free.

100 g of avocado has a daily intake (%) of:

  • 160- 245 calories (kcal).
  • 20% total fat (16g, 30% of avocado pulp): only 5% saturated
  • 2% total carbohydrates (8g): 12-28% dietary fiber
  • 12% potassium (500mg)
  • 20% copper (0.2mg)
  • 20% vitamin K (22 mcg)
  • 16% vitamin C
  • 15% vitamin B6

Avocado also contains vitamin E, D, calcium, iron, phosphorus, magnesium, zinc, manganese, Thiamine, Riboflavin, and Niacin (234)

Avocado Plant Information

All avocado varieties belong to the Persea americana species of the Lauraceae family. The avocado is a deciduous tree that can be propagated by seedling or grafting. A mature tree can become quite tall, reaching up to 18-20 m (66ft), with a 30-60 cm trunk diameter. The leaves have an alternate arrangement with a size and shape that varies depending on the variety. Usually, when young, they are hairy, and as they mature become smooth and leathery. Each tree can produce many thousands of perfect flowers, of which usually only 5% of them are fertilized and produce avocado fruits. However, if the environmental conditions are not favorable, there is a possibility that the trees grow but do not produce fruits (5). The avocado cultivars usually have significantly different harvesting moments, while there is also a great time variation between the flower moment and the fruit ripening and harvest (from 4 to 10 months). Young plants need extra care and protection from hot sun and strong winds, and they usually enter their reproduction life at the age of 4-5 years. However, it takes another 4-5 years to reach their maximum yield potential. The combination of different fruit trees, intercropping, is quite common by cultivating avocado on the same field with mangos, citrus, palm trees, and even olive trees. The tree cannot tolerate the hot, dry winds and frosts, but it needs warm weather and a sufficient water supply (rainfall or irrigation) to produce fruits. Suppose the climatic conditions are favorable and the water supply is sufficient. In that case, avocado is an easy crop to handle, with not very high needs for fertilization and crop protection. Thus, organic cultivation is a possible and viable solution. However, climate change makes it more and more difficult for avocado growers to preserve their orchards, and it already has an apparent negative effect on yield.

Depending on the variety, the fruit has a pear-, egg-, or spherical shape, a smooth or speckled, leathery skin of green color that in some cases becomes purple, dark brown, or even black when the fruit ripens. The flesh has a buttery texture and a light green to yellow color. In the center of the fruit, there is one single large seed enclosed in two brown, thin, papery seed coats (Morton, 1987). The fruit produced from modern cultivars may weigh from 150 to 400-500g, with a length that usually varies between 7 and 20 cm (6). Since it is a climacteric berry, avocado continues to ripe even after it has been detached from the tree (harvested). The farmer needs to be extra careful during harvest and storage of the fruits to avoid damaging them. The storage and shelf-life greatly depend on the ripening level of the fruit during harvest, the variety, and the (storage-environmental) temperature.

Attention: A farmer needs to carefully study the needs of avocado plants for environmental conditions, ensure water availability, and choose one or preferably, more suitable varieties to cultivate. The crop needs multiple years to start producing fruits. Planting an avocado orchard in an unsuitable position can cost the farmer money and years of production. A failure of avocado trees to produce fruits even after 5-6 years may be attributed to the lack of a pollinator variety in the field (or sufficient trees of it) or the local microclimate.

References

  1. https://avocadosfrommexico.com/avocados/history/
  2. https://californiaavocado.com/nutrition/avocado-nutrition-facts/
  3. https://www.fao.org/3/X6902E/x6902e06.htm
  4. https://fdc.nal.usda.gov/
  5. https://link.springer.com/content/pdf/10.1007%2F978-3-319-06904-3.pdf
  6. https://academicjournals.org/journal/AJPS/article-full-text-pdf/9F08F0F56344#:~:text=The%20avocado%20fruit%20has%20a,long%20(Morton%2C%201987).

Morton JF (1987). Fruits of warm climates. Julia F. Morton, Miami, Florida, 505p.

History, Nutritional Value and Plant Information of Avocado

All Avocado Varieties Explained- Characteristics and Advantages

Avocado Tree Climate and Soil Requirements – Planting Avocado Trees

Avocado Tree Propagation and Pollination

Avocado Tree Water Requirements and Irrigation Systems

Avocado Fertilizer Requirements

Training and Pruning of Avocado Tree

Avocado Harvest, Yield per hectare and Storage

Avocado tree Pest and Diseases – Avocado Weed Management

 

Repellent and/or insecticidal plants, traps, and natural enemies handling are some very easy and efficient ways to control important crop pests, especially for smallholders and family farmers.

It is known that a large number of plants naturally exhibit repellent and/or insecticidal activities. This natural botanical activity has led to the characterization of these plants as “phytoinsecticides“. Taking advantage of the intrinsic phytoinsecticidal potential of this biological tool, it can be introduced, whenever possible, on farms as an alternative means of supporting crop pest management. 

The repellent and/or insecticidal plants can be planted on the borders of the main crops, in an intercropping, or distributed freely among the crop plants. 

Among the different plant species having this ability-characteristic, the following ones stand out: 

  • Mammea americana 

Aids in the control of caterpillars Diaphania spp, Spodoptera frugiperda, and the insect Plutella xylostella; 

  • Ruta graveolens and Allamanda nobilis 

Aids in aphid control; 

  • Mentha piperita and Tanacetum vulgare 

Acts as an ant repellent; 

  • Calendola officinalis 

General insect control; 

  • Coriandrum sativum 

Mite and aphid control; 

  • Sapindus sapona 

Helps control stored grain pests; 

  • Urtica Urens 

Control of aphids and repellent to the bug Phthia picta; 

  • Delphinium sp. 

Locust repellent; 

  • Cymbopogon winterianus 

Housefly repellent; 

  • Rosmarinus officinali and Pelargonium graveolens 

Repels pests and insects; 

  • Cymbopogon citratus 

Cabbage aphid repelling aid Brevicoryne brassicae; 

  • Tagetes erecta 

Repels whiteflies and fights nematodes; 

We recommend that farmers plant as many of these plants as possible throughout the property in order to find the optimum combination and have the best results.

Tomato plants with coriander to assistant combat tomato moth and whitefly

“Agroecological traps to capture biological agents identified as pests.”

One way to combat the pests that fly is to use a simple trap that contains a solution attractive to the insect. Widely used in commercial crops but little known to small and medium farmers. 

The trap is very cheap to make it. All you need is to build a disposable pet bottle for each trap.

A caching solution is placed inside the translucent white pet bottle, capable of attracting the insect into the bottle and leading to its drowning in the solution. The attractive solution should be sweetened, such as by example, a natural fruit juice, and should preferably be yellow. (Dilute one part of pulp to four equal parts of water).

Assembly 

Step 1: Drill four holes with one centimeter of radius at 90 degrees from each other, just above the middle of the pet bottle. All should be on the same line as the outer perimeter of the bottle.

The holes drilled in the pet bottle will serve as an entry point for the insects. You should open a maximum of 4 holes at 90 degrees to prevent the insects from escaping the trap.

Step 2: Remove labels and clean the outer surface of the pet bottle to keep it completely transparent and prevent the trap from becoming less attractive to the insect. 

Step 3: Depending on the size of the area, place two to four traps per hectare.

Hung the trap on a branch that is more peripheral and less exposed to the sun, just above the middle of the fruit trees.

In the case of shrub crops, it will be necessary to use slanted stakes (20 to 45 degrees vertically) so that the pet bottom surface of the bottle is a few centimeters above the top of the tallest leaves.

It is also suggested to place a trap close to and just above each compost pile, biofertilizer, and biopesticide tank.

The attractive solution must be renewed and refreshed by the same or a different attractive solution immediately when you realize that the insects are no longer attracted to the solution or when the trap is cleaned to remove the captured insects.

Every week or at most every fortnight, when discarding the dead insects, you should change the liquid in the pet bottles. Rinse the container with water to remove the residue from the old attractive solution before placing the new one. Traps should be replaced every four months and taken to garbage recycling sites.

“Fruit fly trap”

Fruit flies (Anastrepha fraterculus and Ceratitis capitata) are also known as “fruit bugs” or “guava bugs.”

These insects cause direct and indirect damage to the fruits and, thus, reduce their commercial value.

To help solve the problem, you can use a trap that allows the multiplication of a wasp species (Canaspi Carvalho) that is a natural enemy of the fruit fly.

Material needed:

Plastic mosquito net screen with mesh 2 mm;

Hoes and shovels for trenching.

How to assemble the attractive trap:

Step 1: Ditching: Dig a small trench 30 cm deep x 30 cm wide x 30 cm long;

Step 2: Preparing the screen: Cut pieces of screen 35 cm wide x 35 cm long;

Step 3: Wasp attraction: Place the first fruits of the crop in the ditch;

Step 4: Covering the ditches with the screen: Cover the trench with the screen, taking care to place soil about 5 cm from all sides of the screen so that it is well fixed to the ground and does not allow the entry of animals and/or the escape of the larvae.

How it works:

The fly larvae inside the fruits placed in the trench will turn into adults. From there, the tiny wasp will pass through the 2mm opening in the screen and lay its eggs on the fruit fly adults that remain in the trap. The wasp reproduces on the fruit fly adults quickly and will leave the screen, multiply more and more, performing a natural pest management.