Blackberries, like raspberries, are quite sensitive to many diseases and pests. Still, the severity of a problem highly depends on the environmental conditions of a region, the crop and disease history of a field, and the variety cultivated. The farmers should follow the local announcements and guidelines from the relevant authorities that can inform them concerning the population of an insect, the risk level of a disease infection, and the moment and type of control measures to be applied.
Which are the most important insects of blackberries, and how to control them
The most common insects that can attack blackberries are aphids, mites, strawberry weevil, red-necked cane borer, raspberry crown borer, thrips, stink bugs, gall midges, and beetles. However, in a vigorous crop, there is rarely the need for chemical control of these pests. You are strongly advised to avoid any preventive spraying and use insecticides only when necessary, as advised by a licensed agronomist or local authority. Always use chemicals that do not harm the pollinators (avoid spaying during flowering) and protect the natural enemies of the crop pests.
Aphids are tiny, sap-sucking insects and members of the superfamily Aphidoidea. They puncture the plants' stems and leaves, leaving a substance called honeydew. The honeydew, as the name suggests, is a sticky substance that attracts other insects like ants. Aphids are also carriers of plant viruses. Other common symptoms are curled and yellow leaves. Aphids are mainly controlled by natural enemies (predators) of the insect. The use of pesticides is possible but usually not necessary.
Spider Mites (Derryberry and Redberry Mites) are members of the Acari family Tetranychidae and can develop a large population, posing a threat to blackberries during hot, dusty weather. They are tiny pests that usually live and feed on the underside of the leaves. They can be detected during the growth season (mid-spring until mid-autumn) and are usually naturally controlled by insect predators (mites and beetles). Applying lime and wettable sulfur in early spring (before and at the start of bud break) can effectively control the pests. Chemical control is possible, but it is not suggested due to the ability of mites (like aphids) to develop resistance.
The insect borers can infest blackberries, and despite some differences in their life cycle, the main problem is caused by the feeding of the larvae inside the plant (canes, crowns, roots). This activity usually leads to limited growth and vigor of the infected plant organ, which sometimes wilts and dies. The use of insecticides (e.g., Pyrethroid, Chlorantraniliprole, or organophosphorus insecticide) is possible, but there is a very narrow application window since the insect remains inside the plant most of the time. Pruning and removing the infected parts of plants is the most effective management method.
Which are the most important diseases
Some significant diseases that can damage Blackberries are Cane Botrytis, Blossom Blight, Fruit Rot, Grey Mold, Root, and Crown Rot (Phytophthora sp. and Rhizoctonia sp.).
The first four diseases are caused by one fungus called Botrytis cinerea. Botrytis causes soft rot and mainly infects flowers and fruits. A common disease symptom is the water-soaked, soft rot appearance of the infected plant parts covered by dense grey fuzzy fungal growth. Prolonged rainy and humid weather during the flowering stage of blackberries can increase the risk and the development of the infection. The farmer should be extra careful when harvesting because the damage to the fruits can be extended and spread during fruit storage. To limit post-harvest losses, the grower should collect healthy, firm berries and cool them immediately after harvest. Chemical control is available and suggested when favorable conditions for the fungus prevail. However, it is more efficient to combine cultural control measures that reduce humidity and facilitate aeration of the canopy (e.g., pruning, drip irrigation instead of sprinklers, etc.).
Phytophthora root rot (Phytophthora fragariae var. rubi) is one of the most serious diseases worldwide for Blackberries and Raspberries. It can cause severe damage to susceptible blackberry varieties and plants grown in soaked soils. The fungus causes plant thinning and the production of fewer canes each year. Primocanes and floricanes seem to develop normally, but then they wilt and die suddenly when the weather becomes warmer. Both Root and Crown Rot (Phytophthora sp. and Rhizoctonia sp.) cause brown or purplish lesions on new canes and the roots, resulting in yellow or dwarfed plants. It is recommended to use certified healthy plants and semi-resistant varieties, plant in raised beds (especially in poorly drained soils), and spray with suitable fungicides (only when it is absolutely necessary).
Anthracnose is a disease caused by the fungus Elsinoe veneta that more commonly infects Blackberries and black raspberries (extensive host range). The symptoms, which are sunken pits and purple spots (with a light grey center), usually appear on the cane, but in extensive infection, they can also appear on the leaves and petioles. The spores of the fungus are carried by splashing rain or irrigation, infecting other plants. Most of the fungi thrive in wet soils and humidity. The control measures for the disease can also effectively control the Spur Blight. The farmer can limit the risk of infections by improving the aeration of the canopy, avoiding wetting the leaves, and removing the diseased plant parts. Additionally, liquid lime sulfur can be used during the initiation of budbreak to control the disease successfully.
Some viruses can affect the fruit and plant, but blackberries are generally more tolerant than raspberries. However, there is no treatment for viruses. If you are certain that a virus has infected your plants, you must remove them entirely and dispose of them elsewhere (far from the field) so the virus does not spread.
To preserve your blackberry's health, you must build an unwelcoming environment for pests and diseases. The best practice, of course, is prevention, especially for viruses. You can grow Blackberries in the sun. You can water regularly, but also keep the soil well-drained to prevent insects from coming. You can also remove any dead leaves, flowers, or fruits and dispose of them in different places. Moreover, you can remove any unwanted weeds that can attract various insects. If you have done all that and your plants still suffer, you can seek advice from your local agronomist or scientist. However, please consult your local licensed agronomist to obtain chemical control recommendations for these Blackberry pests and diseases.
Weed management in blackberries
Weed management is also necessary for blackberries to control perennial weeds' growth, which can suffocate the crop and make common cultivation activities difficult. During the preparation of the planting site, it is essential to remove all weeds growing to decrease the competition with the blackberry plantlets during the first couple of years of growth. For this, the farmer can use herbicides, tillage, and cover crops (that should have been established months earlier). After the crop has been established, most weed management concerns the enter-row space. When trailing thornless blackberries are cultivated, hoeing, mechanical cultivation, and mulching may be needed to keep the field weed-free. However, in the case of erect varieties, the dense canopy can produce sufficient shade that decreases weed growth. As a complementary measure, the farmer can apply herbicides banded along the row, mulch along the edges of the hedgerow, establish a permanent cover crop (e.g., bluegrass, orchard grass, etc.), and shallow cultivation (max 2 inches or 5 cm deep). Using a strip of black plastic placed around the plants (not too close to the base) has been proven to be the most effective measure of weed and sucker control. In all cases, it is essential not to damage or obstruct the emergence of new primocanes and the shallow root system of blackberries.
References
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https://ag.missouristate.edu/assets/MtnGrv/B39GrowingBlackberriesinMissouri.pdf
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http://www.extension.uidaho.edu/publishing/pdf/BUL/BUL0812.pdf
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https://extension.okstate.edu/fact-sheets/blackberry-and-raspberry-culture-for-the-home-garden.html
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https://extension.okstate.edu/fact-sheets/blackberry-and-raspberry-culture-for-the-home-garden.html
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https://www.vgls.vic.gov.au/client/en_AU/search/asset/1281488/0
Further reading
- Blackberry Nutritional Value and Health Benefits
- Blackberry vs Black Raspberry - Similarities and Differences
- Blackberry Plant Information - How to Identify Blackberries
- Site Selection, Soil Preparation, and Planting of Blackberries
- Blackberries Propagation and Pollination
- How to Prune and Train Blackberries
- Water Needs and Irrigation of Blackberries
- Nutrient Needs and Fertilization of Blackberries
- Blackberry Pests, Diseases and Weed Management
- Blackberry Yield, Harvest, and Storage