– David Owens, Extension Entomologist, owensd@udel.edu
Begin scouting strawberry for two spotted spider mite and tarnished plant bug. With the cooler winter we had this year, mite populations may be slower. In 2020, we had strawberry plots in Georgetown with plants from two different nurseries. One of them had much higher mite counts in the spring than the others, suggesting that the transplants were already infested in the fall of 2019 going into winter. Thresholds early in the year are 5 mites per leaflet, but once berry harvest begins, thresholds increase to 20 per leaflet. Sample 10 leaflets per acre. Use of a hand lens is highly recommended. If you have good eyes in strong light, you may be able to get by with a visor lens at 3.5x, but a hand lens with 10x magnification is preferable.
While sampling for mites, also sample for tarnished plant bug. Tarnished plant bugs are small, mottled brown, sucking insects. Nymphs are a light green, gradually developing black spots as they grow larger. Feeding injury will show up as deformed berries with fully developed seed. This differs from poor pollination, in which some of the seeds are not going to be developed. Sample 1 plant every 20’ by beating the plant on the black plastic or over a beat sheet. One bug per 20 plants is enough to warrant an insecticide treatment. Keep in mind, this insect is more likely to cause problems in late maturity group berries as its populations build up in weeds, some of which may start senescing by the time the latest varieties start producing. If you decide to use an insecticide, there are numerous options, including Malathion, various pyrethroids, Assail, Transform and Closer, Apta, Cormoran, and Beleaf. Of these, Beleaf has low toxicity to bees and the active ingredient is widely used in southern states for tarnished plant bug in cotton. It also has a 0 d PHI. Apta has powdery mildew activity. Probably the best organic option is Azera, a mixture of azadirachtin + pyrethrin.