Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
We are now about 3 weeks past flowering in wheat and symptoms of Fusarium Head Blight (FHB) are becoming visible (Figure 1). At this point, symptoms have been at very low incidence across the region. It is possible for cool weather to delay symptom development, so continue to scout as fields approach 3-4 weeks past flowering. We had rainfall throughout flowering that kept the region at high risk, but temperatures were below optimum for spore development. The major concern of FHB is the accumulation of deoxynivalenol (DON). A challenging aspect of cool weather is that plants can have reduced symptoms, but may still accumulate elevated levels of DON. While you cannot scout for DON, you can scout for visual symptoms following the steps introduced in the May 15 WCU https://sites.udel.edu/weeklycropupdate/?p=14901. When assessing FHB incidence, remember to select heads randomly to not bias your sample. If you have high levels of FHB in your field, or in part of a field, you may want to consider harvesting as early as possible. Increasing the fan speed at harvest can help to remove lightweight, diseased grain with chaff. This technique is feasible when the rest of the grain is of good quality; the goal is to blow the lightweight, diseased kernels with high DON without blowing out heavier high-quality kernels. It is also best to dry grain to at least 15%, and store grain with FHB issues separate from cleaner grain.
Figure 1. Wheat head with bleaching and orange sporulation due to Fusarium Head Blight
I have observed a few varieties, particularly in barley, where grain fill was impacted by frost events. Injury and premature death can favor black head molds. Multiple fungi can cause these molds that give tissue a “dirty” or weathered appearance (Figure 2). Review notes of which fields may have had frost damage to aid in scouting.
Figure 2. Barley heads that did not fill grain due to frost damage now covered with black head molds