David Owens, Extension Entomologist, owensd@udel.edu
With a worsening drought, any small grains that are up, are at risk from aphid damage and from winter grain mite. Fall aphid treatments are primarily aimed at preventing barley yellow dwarf, but this year we may see direct injury due to lack of soil moisture. If greenbug is present in a field, you may want to treat the field. There are thresholds for greenbug, they tend to be a little bit higher than the other species, but with dry soils, plants will struggle to grow and their feeding effects more impactful. States use different thresholds for other species, with 1-2 bird cherry oat aphids per row foot during the first 30 days after planting and 6-20 aphids per row foot in the fall before winter being commonly used thresholds. Higher numbers can probably be tolerated in wheat, many varieties of which have some degree of tolerance to BYDV. Again, this year you may want to be more aggressive on aphids. Due to lack of soil moisture, aphids may concentrate themselves in small grains more than usual, particularly irrigated small grain. If you do need to treat, all three aphid species (greenbug, bird cherry oat aphid, and greenbug) are susceptible to pyrethroids. In barley, we do have the option of using Endigo, which has thiamethoxam in it, providing longer residual.
Winter grain mite is another pest I almost never discuss because our small grains generally get good growth and ample soil moisture this time of year. However, last year in late winter I was sent photos from Pennsylvania showing fields with severe winter grain mite defoliation. Joanne Whalen put together a winter grain mite fact sheet: https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/winter-grain-mite/. This is a pest of small grains following corn, especially no-till corn. Joanne noted that tilled fields tend to have less mites. Winter grain mite is active at night or on cloudy days. First thing in the morning look at the base of plants. Winter grain mite eggs should be hatching now, you will want to pay attention to this pest in late Fall and into the winter. Adults are active in December, and another generation from late February through early April. Look for signs of silvering where mites had been feeding. If heavy feeding signs are present and, according to OSU, large numbers of mites are present (10+ per plant), control may be warranted. If an insecticide is necessary on this species, pyrethroids and dimethoate may help reduce them (and certainly will for aphids).