Alyssa K. Betts, Extension Field Crops Pathologist; akoehler@udel.edu
This week barley is around flag leaf and approaching heading while wheat is ranging from Feekes 6-8. This week has been colder, with hopefully the final frost. The frost Wednesday morning was one that varied by location and microclimate. This can sometimes result in variable foliar symptoms across a field, such as browning of the leaf tips. Barley Yellow Dwarf Virus (BYDV) symptoms often become visible around flag leaf and there can be confusion across frost and BYDB symptoms. Powdery mildew is also showing up in a few areas following the cool weather this week. Fusarium Head Blight (FHB), caused by species of the fungus Fusarium, is typically the most important disease of small grains in our region. Last year we saw higher disease pressure than the previous two seasons. We have rain in the forecast this weekend but drying out in the current extended forecast. The Fusarium Risk Assessment Tool (www.wheatscab.psu.edu), a forecasting model that uses current and predicted weather forecasts to predict FHB risk, is live for the season and we are currently at low risk (Figure 1). The pathogen that causes FHB infects through the flower and rainfall 7 to 10 days prior to flowering favors spore production and increases risk of infection. In barley, flowering begins just before the spike emerges from the boot. While florets are not as susceptible, Fusarium can infect the glumes and produce deoxynivalenol (DON). DON accumulation is the primary concern, especially for malting barley acreage. If making a fungicide application to manage FHB in barley, the optimum stage to protect barley glumes is when the spike has fully emerged from the boot and florets are exposed (Figure 2). Work in North Carolina has shown that application up to 6 days after 100% emergence can reduce infected kernels and DON in barley.
Figure 1. Fusarium Risk Assessment Tool screenshot of predicted risk for April 10, 2025, www.wheatscab.psu.edu
Figure 2. Stages of barley at or near spike emergence, with the two right spikes (100% emergence and 6 days after) at optimum stage for fungicide application.