David Owens, Extension Entomologist, owensd@udel.edu
Small Grains
Wheat and barley will soon be going in the ground. Crops planted before the ‘Fly Free Date’ (October 3 for New Castle, October 8 for Kent, and October 10 for Sussex) may benefit from a neonicotinoid seed treatment for both hessians fly and for aphid management. I have not heard of significant hessian fly activity on Delmarva for a very long time, but it is worth keeping in the back of the mind. Many wheat varieties have some degree of resistance to Hessian fly. If you are concerned about it, reach out to your seed dealer to find out if your variety’s response is known.
Scout for aphids this fall. The three species of aphids that get into small grain are bird cherry oat aphid, English grain aphid, and greenbug. Greenbug and English grain look very similar. Greenbug tends to have a turquoise blue stripe down the back, and it will have short, green cornicles. English grain aphids have long, black cornicles. It can be difficult to differentiate small nymphs. Greenbug saliva is phytotoxic to the plant and thresholds for this aphid are lower than the other two. Bird cherry oat aphid is generally associated with more severe BYDV. Thresholds during the seedling stages from southern states are 1-2 bird cherry oat aphids per row foot or 10 greenbugs per row foot. Once we move into mid-late November, those thresholds are variable. Some states use a threshold of 6 aphids per row foot and others use a threshold near 20 aphids per row foot. If a foliar treatment is necessary, pyrethroids do a good job on all aphids in small grains. For barley, Endigo can be used and will provide even longer residual. Dimethoate (wheat only) and Sivanto are also options.
We had a lot of BYDV in 2023, and I suspect it was due to an unusually warm February. BYDV incidence was less this year, but it was still present. Wheat varieties may have different levels of susceptibility to BYDV, and neonicotinoid seed treatments probably won’t pay for themselves in wheat, based on some long-term data from southern states. Barley is different, and more susceptible to BYDV, and I would suggest being more aggressive on aphids in barley and especially in malt barley.
The best compilation of research on aphids and barley yellow dwarf can be found here: https://smallgrains.ces.ncsu.edu/wp-content/uploads/2024/02/BYDV-in-the-SE-ANR-1082-compressed.pdf?fwd=no.