Apricot Pests, Diseases, and Physiological Disorders

Apricot Pests and Diseases

The plant protection of Apricot trees against various pests and diseases is usually necessary, especially in cases where apricot is grown in large areas (monoculture, many apricot fields together), and the environmental conditions are often favorable for the propagation and spread of these enemies. 

In general, chemical control against pests often starts during the second year of plant establishment. Some applications may be necessary during mid to late winter to protect the trees against insects that can cause significant damage to the young trees like peach twig borer, San Jose scale, aphids, and mites. Due to the small tree size, it is vital to use the reduced dosage and the instruction mentioned in the product (consult your agronomist). The protection against pathogens like fungi and bacteria usually begins during the 3rd year, with some treatments at full bloom. In all cases, it is essential to visit your orchards often, monitor the pest/pathogen population and environmental conditions, and follow the instruction of the local relevant authorities and the specifications of each product mentioned on the label (dosage, number of applications, spectrum, etc.). 

There are two strategies for pest and disease management (a combination of the two is also possible). The first is the preventing approach, and the second is curative. In the first case, the grower applies a series of applications with insecticides or/and fungicides routinely without having any actual evidence of the presence of an enemy or symptoms (damage). For example, it is common to spray with insecticides three times per year, starting from the petal fall stage and in 10-14 days intervals, or with fungicides when the weather is favorable for the spread of disease (rainy). While this strategy can efficiently protect your trees, it has a high environmental and economic footprint and is used by farmers that do not feel comfortable monitoring the pest number or recognizing the different pests/pathogenes or symptoms. On the other hand, the curative approach requires more effort. Still, it is the best way to apply plant protection since it also allows the build-up of beneficial organism populations (which can help control important plant pests). 

Attention:

1. Avoid applying pesticides or products that could harm the bees foraging in your orchard during the flowering of the apricot trees.
2. If pest control is absolutely necessary at that moment, always use bee-friendly products exclusively and apply them during late afternoon or night when the bees are not active.
3. In every case, inform the beekeepers close to you before applying.  

Apricot important Pests

Most plant protection against pests takes place from late spring until mid-summer. The most important apricot pests are the following: 

Oriental Fruit Moth

The Oriental fruit moth is the most common and serious pest of Apricots but is capable of infesting other fruit trees as well. The insect Grapholita molesta (Order: Lepidoptera) causes severe damage to fruits due to the activity of the larvae that feed and open holes in them. These damages dramatically reduce the commercial value of the fruits that are unsuitable for the fresh market (and usually for the industry as well). We may start to observe wilting leaf tips by the time the insects have been attached to our Apricots.

Mealy plum aphid

Hyalopterus pruni is the main aphid that attacks apricots, causing a developing reduction rate when the population is too high. The honeydew produced by the aphids favors the growth of fungi that can further decrease the product’s commercial value (if the fruit is infected) or reduce the photosynthetic ability of the canopy (when it covers the leaves). 

Once the crop has been attacked, efficient management is difficult because these pests develop immunity (quickly) against pesticides. Close monitoring of their population will allow the farmer to control the insect in an earlier stage (early in the season) before developing a large-damaging population and start feeding on the fruits. Moreover, integrated pest management practices may be very effective as well. Pheromone traps are a commonly used technique. Attracting the male insects prevents mating with the females, decreasing the next generation’s population significantly. Another commonly used method is the use of predators (pest’s natural enemies). There are several commercial products that contain living predators able to attack pests in various development stages, most commonly the eggs, and significantly reduce their population. 

Borers (Greater Peachtree (Crown) Borer and Peach Twig Borer)

Except for apricots, other fruit hosts of these borers species are the peach, nectarine, and plum. The damage is caused by the larvae that create tunnels on the trunk (at the cambium close to the soil line) or the branches and shoot tips (depending on the species). The farmer may observe oozing tree sap (gum) mixed with frass coming out from the tunnel opening, dead twigs/shoots, holes in fruits (from the Peach Twig Borer), and even the dieback of the tree canopy (from the Crown Borer). 

In years that management of the insects is necessary, the (conventional) grower may spray with permethrin or carbaryl in early summer on the trunk close to the ground or the canopy (pyrethroids and malathion). In organically cultivated apricot orchards, growers may use spinosad, beneficial nematodes (for the Crown Borers), and Bacillus thuringiensis (for the Peach Twig Borers) products. 

Keep in mind that the species and population (damage) of pests may differ from one region to another. 

Apricot Diseases

Bacterial canker

The disease is caused by the bacterium Pseudomonas syringae, which causes characteristic gum, cankers, and spots at leaves, blast flowers, and shoots. Buds may die if infected. The symptoms are more easily observed during spring and pruning when we may observe an amber-colored gum coming from the wounds. The disease is favored by high moisture and cool temperatures, while extensive problems may occur in sandy soils with shallow claypans, in locations with high numbers of ring nematodes and spring, and in locations where frosts are common. Vigorous trees are less susceptible. 

In fields with known disease history, the farmers should fumigate the soil properly (apply nematicides) before replanting apricot trees and avoid using susceptible to bacterial canker rootstocks (like Myrobalan, Marianna 2624, etc.).

Eutypa dieback – Gummosis

The disease is caused by the fungus Eutypa lata. Some common symptoms are the chronic canker on branches (the leaves remain attached to the dead twigs) with typical brown discolorations of the tissue inside that sometimes is combined with gummy amber exudate.  

Disease control begins with proper precautionary measures. These include weed control, safe distances between plants, proper drainage, and avoiding foliar wetting. Additionally, it is essential not to prune the trees when the weather is rainy or with high humidity. The infected libs should be pruned, cutting at least 1 foot below the infected area. This activity should take place in late summer. The wounds should be treated with fungicide, paints or sealants. Mummified fruits should be removed from the field. The general condition of the plants (nutrients and water level, sun exposure) can also boost their tolerance to the pathogen. Chemical treatment is used only if the problem is severe and always under supervision from a local licensed agronomist. Using proper sanitation, such as tools disinfection every time we touch the plants, is also crucial.

Shot Hole

The shot hole is a disease caused by the pathogen Stigmina carpophila. As the name of the disease suggests, symptoms include dark spots resembling gunshots on the leaves, stems, and fruits, decreasing their commercial value. Additionally, the disease may damage the buds during the dormancy period. 

Disease management may start during winter, and it is crucial if the weather is expected to be rainy. The applications with fungicides also continue during the flowering period (the number depends on the environmental conditions). 

Powdery Mildew

Sphaerotheca pannosa and Podosphaera tridactyla cause extensive damage to apricots. We may observe chlorotic spots on infected plants with a characteristic whitish powder resembling flour on leaves, stems, flowers, and mature fruits. Sometimes, on the fruits, these spots take a red-purple color. 

While fruit becomes relatively resistant to new infections after the pit-hardening stage, the farmer should apply suitable fungicides before starting in full bloom. 

Brown Rot (Blossom and Twig Blight)

Brown Rot, caused by the fungus Monilinia (M. fructicola and M. laxa), is the most important disease of the Apricots. The fungus infects flowers, young shoots, and mature fruits, causing a significant decrease in production. 

The farmer should apply proper weed control, plant the trees at safe distances, ensure proper drainage and avoid foliar irrigation. Diseased twigs and mummified fruits should be removed from the tree and the field ground. The general condition of the plants (nutrition and water availability, sun exposure) can also boost their resistance. It is also crucial to use proper sanitation, such as tools disinfection every time we touch the plants. Chemical treatment (2-3 fungicide applications during flowering) is used only if the problem is severe and always under supervision from a local licensed agronomist.

Sharka

Plum pox, or sharka, is a disease caused by the shark virus, which causes chlorotic spots on leaves combined with yellow rings on the fruits. 

There is no treatment for viral diseases except for buying disease-free plants from a legitimate seller. 

Physiological Anomalies-Disorders

Most producers will face two main physiological anomalies inside their apricot orchards which are:

1. Sunburn

Newly-planted apricots are sensitive to bark sunburns because their young tissues are easily damaged by intense sunlight. Many producers used to paint the young barks with dilute white paint to protect them; however, nowadays, you can find more accurate solutions in the market (consult your agronomist).

2. Gummosis

Gummosis is the oozing of sap from tree barks that are either mechanically injured, stressed, or infected by pathogens. If the symptoms occur since a pathogen like Cytospora canker infects the tree, growers should consult their agronomist for a cure as soon as possible. If the symptoms, however, are not pathogenic, all you have to do is maintain your plants healthy, avoiding stressful conditions and injuries. 

References

• https://coststudyfiles.ucdavis.edu/
• https://extension.usu.edu/pests/research/backyard-apricot-pests
• https://www2.ipm.ucanr.edu/agriculture/apricot/

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Apricot Pests, Diseases, and Physiological Disorders