Alyssa K. Betts, Extension Field Crops Pathologist; akoehler@udel.edu
Symptoms of Fusarium Head Blight (FHB) have been visible in barley and are now present in wheat. You will be looking for bleached spikelets while the rest of the head is still green (Figure 1). Although the season started at low risk, weather conditions shifted right at the start of flowering and have kept us at high risk over the past 2-3 weeks (Figure 2). Tips for scouting for FHB were shared in the update last week. Now is a good time to walk fields and assess the level of FHB present. If you look at infected kernels, they are usually shriveled and lightweight, commonly called tombstones. The fungus that causes FHB produces a mycotoxin, deoxynivalenol (DON). Symptoms do not automatically mean DON is present and it is possible to have high DON even when symptoms are low. However, if there are a lot of damaged kernels, it is likely DON is present. Grain moisture must fall below 13 percent to stop accumulation of mycotoxin, so DON can continue to increase if harvest is delayed. Mycotoxins are typically most accumulated in the tombstone kernels. With their light weight, they can be separated from healthy grain by increasing fan speed of the combine. If storing it is very important to properly dry grain. DON is stable so drying and storing will not reduce the harvested DON level, but DON concentrations will not continue to increase when grain is properly stored.
Figure 1. Wheat head with bleaching and orange sporulation due to Fusarium Head Blight (top), Barley heads with symptoms of FHB (bottom)
Figure 2. FHB Risk Model for May 23, 2024