Blackberries (Rubus species) are a highly favored fruit crop, prized for their complex flavor and nutritional benefits. However, the delicate nature of the canes and the fruit makes them particularly susceptible to a range of insect pests. Infestations can quickly lead to significant reductions in both yield and fruit quality if left unmanaged. Implementing a focused pest control strategy is necessary for maintaining healthy plants and ensuring a successful harvest. This guide identifies common blackberry pests and provides effective management techniques.
Identifying the Most Damaging Pests
Spotted Wing Drosophila (SWD)
The Spotted Wing Drosophila (SWD) (Drosophila suzukii) is a small, invasive fruit fly, roughly an eighth of an inch long, with a yellowish-brown body and characteristic red eyes. Male flies are distinguished by a single, dark spot near the tip of each wing. Females possess a large, saw-like ovipositor, which they use to slice into the skin of healthy, ripening blackberries to deposit eggs just beneath the surface.
The larvae are small, white, legless maggots that develop and feed inside the fruit. This internal feeding causes the berry to rapidly soften, collapse, and become mushy. It often introduces secondary pathogens like fungi and bacteria, accelerating fruit deterioration and making the fruit unmarketable. Infestations are most severe during the warm summer months when the life cycle can complete in as little as 10 to 14 days.
Blackberry Cane Borers
Blackberry cane borers are insects whose larvae tunnel through the canes, causing structural damage and hindering nutrient flow. The Rednecked Cane Borer (Agrilus ruficollis) adult is a slender, metallic beetle with an iridescent coppery-red thorax. The tell-tale symptom of this pest is the formation of a noticeable, cigar-shaped gall, typically one to three inches long, on the primocanes (first-year canes).
This gall is a reaction to the larva tunneling in a spiral fashion just beneath the bark, which can cause the cane to die or become weakened. The Raspberry Crown Borer (Pennisetia marginatum) is another significant pest, a clear-winged moth that resembles a yellow jacket. Its larvae tunnel down into the crown and roots, often causing the entire cane to wilt and break easily at the base, leading to plant destruction over its two-year life cycle.
Redberry Mites
Redberry mites (Acalitus essigi) are microscopic eriophyid mites, nearly impossible to see with the naked eye. Their presence is diagnosed entirely by the damage they cause to the fruit, often referred to as “redberry disease.” These mites feed at the base of the individual drupelets (the small sections that make up the blackberry) and inject a toxin.
This toxin prevents the affected drupelets from developing their mature color, causing sections of the otherwise ripe, black berry to remain bright red, hard, and sour. This patchy ripening is a distinctive sign of infestation. The mites overwinter in the bud scales and bark crevices, migrating to the developing fruit in spring.
Proactive Management and Cultural Practices
Preventative measures focus on creating an environment that discourages infestation. Proper sanitation significantly reduces overwintering sites for many insects and disease pathogens. This involves the systematic removal of all fallen fruit, leaf litter, and old, decaying canes from the planting area.
Pruning techniques are especially important for disrupting the life cycles of cane borers. Floricanes (second-year canes that have finished fruiting) must be removed immediately after harvest. Since cane borer larvae often overwinter inside these older canes, cutting them out at ground level and destroying them prevents the next generation of adults from emerging. Additionally, any canes showing the tell-tale galls or wilting should be pruned out and destroyed as soon as they are observed.
Managing the plant canopy helps control pests that thrive in humid, sheltered conditions. Strategic pruning and trellising to maintain a narrow, open row structure improves air circulation and light penetration. This helps the canes and leaves dry more quickly, discouraging mite populations and minimizing conditions favorable for fungal diseases.
Physical barriers offer a non-chemical method of exclusion, particularly against the highly mobile SWD. Covering the plants with fine-mesh netting or row covers, ideally one millimeter or less, before the fruit begins to ripen can prevent the adult flies from laying eggs. While this requires careful management to ensure proper pollination, it is an effective way to protect the crop during the vulnerable ripening period.
Direct Treatment Strategies
When an infestation is detected, targeted treatments are necessary to control the population and protect the harvest. For Redberry Mites, which overwinter in the buds, an application of horticultural oil or wettable sulfur during the delayed-dormant stage—after bud swell but before bud break—can be effective. If the mite damage persists, applications of horticultural oil can be repeated every two to three weeks, from the green fruit stage up to the pink fruit stage, ensuring thorough coverage.
Organic controls provide a less toxic approach to managing common pests like aphids and spider mites, as well as providing some control for SWD. Insecticidal soaps work by smothering soft-bodied pests on contact, while neem oil acts as an antifeedant and growth regulator, disrupting the insects’ life cycles. Applying these products requires complete coverage of the plant and pest, as they offer little residual protection once dry.
For SWD, trapping is a crucial component of a direct control plan, though traps alone are insufficient for population control. Monitoring traps can be easily constructed using a plastic container with small holes, filled with a yeast, sugar, and water solution or a simple apple cider vinegar lure, to confirm the presence of the flies. If SWD are confirmed and fruit is ripening, the application of targeted insecticides may be necessary, with organic growers often relying on spinosad-based products.
Chemical applications should always be considered a last resort and must be timed precisely to maximize effectiveness while minimizing risk. For cane borers, chemical sprays target the emerging adult beetles, often requiring application just after bloom to manage the adult population before they lay eggs. The selection of any product must consider the Pre-Harvest Interval (PHI), which is the mandated time between the final application and harvest, to ensure the berries are safe for consumption.