Blackberry primocanes infested with blackberry psyllid nymphs. The shortened internodes and tightly curled leaves are indicative of blackberry psyllid. Photo: HJB
My blackberry research plots are at the Sandhills Research Station, which is a great place to work for a number of reasons. One these reasons is this the Sandhills have unique pest pressures not easily found elsewhere. Blackberry psyllid (Trioza tripunctata) is one of these pests. Blackberry psyllid adults are small, cicada-like insects, and the nymphs are small and wingless. Both life stages feed on phloem and damage plants. Blackberry psyllids are tightly associated with their overwintering host, pine trees, and because of this, their distribution is closely tied to proximity to conifers. Although there is very little literature on blackberry psyllid, the sources that are available suggest that plantings within 1/8 mile of conifers are at the greatest risk of psyllid damage while those further than a mile from conifers rarely have blackberry psyllid damage.
Adult blackberry psyllids over winter in conifers and move to caneberries in spring (probably April in North Carolina) where they lay eggs. The adults will remain in blackberries for several days, and the characteristic leaf curling will develop after about a week. Very low psyllid numbers can produce this injury. Nymphs will develop on the undersides of leaves, progress through 5 instars, and move into their overwintering host in the fall. Blackberry psyllids likely have only 1 generation in the southeast.
Adult psyllid feeding produces curled leaves and shortened internodes, and at the Sandhills, this damage is mostly on primocanes. This suggests that adults may have moved into plantings later than April, unlike the current available sources suggest. Some canes are affected from the tip down, while others appear to be damaged on the underside of the cane, causing it to curl downward. The nymphs feed from the underside of the leaf and produce wax structures.
Curled leaves also provide refuge for other arthropods. I have found spider mites, predatory mites, thrips, and spiders in these leaves so far this season. Spider mites and thrips are potential plant pests, but predatory mites and spiders are beneficial, so these refugia may provide some benefit to the plant.
Spider mite found on blackberry psyllid damaged leaf. Photo: HJB
Cultural control, in the form of site selection, is the most important management strategy for blackberry psyllid in the southeast. The infrequency of blackberry psyllid damage in commercial blackberry production is likely due to distance from conifers.
For locations where psyllid is a problem, we are investigating management strategies this summer, first looking at systemic insecticides that are effective against other psyllids. I treated several plots with imidacloprid on June 22 and will be collected 2 week after treatment samples this Saturday.