David Owens, Extension Entomologist, owensd@udel.edu
Small Grain
Small grain planting is right around the corner. Barley is the most susceptible to barley yellow dwarf virus spread by aphids. Fall infestations are the most damaging and likely to spread the virus. You may want to consider a neonicotinoid seed treatment on barley, and especially malting barley. This should provide 3-4 weeks of protection from aphids. They won’t eliminate BYDV should the aphids have it, but they will reduce secondary spread. If a seed treatment insecticide is not used, you will want to scout fields beginning soon after emergence. We will be surveying fields again this fall and provide management guidance later on. Wheat varieties tend to have greater BYDV resistance/tolerance, check with your seed supplier. Wheat is also planted slightly later, giving aphids less time to colonize and reproduce ahead of cold weather. I see less need for insecticide seed treatment on wheat because of these two factors, but scouting is still advised. Every year is different. We had widespread BYDV in 2022-2023 following many years in which it was not an issue. Some years we have a lot of aphid activity in the fall and recommend treatments, but last year we had almost no fall aphid activity (despite my concerns otherwise), and only thought a treatment was justified on one, early planted barley field (out of 14 small grains sampled regularly).
Sorghum
Sugarcane aphids continue to be extremely active. The threshold is 30% infested plants through soft dough with localized areas of honeydew present. Consider a plant infested if there is a colony greater than the size of a quarter on a leaf underside. The only effective and recommended insecticides are Sefina, Sivanto, and Transform. Dimethoate will knock them back temporarily, but it doesn’t take long for their populations to recover. In 2019 we did a spray trail on aphids using three different rates of Sivanto and Dimethoate. Aphid numbers decreased by almost 90% 2 days after treatment but had recovered to 40% pre-treatment levels 7 days after treatment and almost to pre-treatment levels by 14 days. Sivanto at its 3 fl oz rate dropped their numbers 95% 2 days after treatment and just about zeroed them out at 7 – 14 days.
Soybean
We should largely be past the big earworm wave, but later planted fields that still have some blossoms or did recently but have not been treated should still be scouted for podworm. Double crop fields treated for podworm should continue to be scouted for looper defoliation and stink bug. Scattered reports of aphids are still coming in. Aphid populations can sometimes crash quickly. If nearing the 250/plant average threshold prior to R5, resample the field in 5-7 days. If aphids continue to increase and plant health deteriorates, a pyrethroid will take them out.