Alyssa K. Betts, Extension Field Crops Pathologist; akoehler@udel.edu
The wet spring had us off to a bit of a slow start, but small grains are rapidly moving as we get some of these warm days. Barley is approaching heading and wheat is ranging from Feekes 7-9. Powdery mildew has been at low levels and with the warmer temperatures continuing, it is unlikely to become much of an issue. 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 low disease pressure across the region, but with the wet spring we have been having we will want to keep a close eye on risk levels this spring. The weather over the next few weeks will determine how large our risk will be this year. The Fusarium Risk Assessment Tool (www.wheatscab.psu.edu), a forecasting model that uses current and predicted weather forecasts to predict FHB risk, is now live for the season (Figure 1). Historically about 70% accurate, this tool aids in assessing FHB risk as wheat approaches flowering and fungicide application decisions are made. 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. Within the map you are able to look at predicted risk for the current day or 2, 4, or 6 days out. You can click to adjust anticipated susceptibility based on the hybrid planted. This is where fall decisions can play a big role in Fusarium management as risk will vary depending on how susceptible the crop is. If you would like to receive text and/or email alerts you can sign up at Scab Alerts.
We are currently at low risk on The Fusarium Risk Tool (Figure 1), but with the rain coming at the end of this week, we move to more of a medium risk in the 6-day outlook (Figure 2). 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 is fully emerged from the boot and florets are exposed (Figure 3). Work in North Carolina has shown that application up to 6 days after 100% emergence can reduce infected kernels and DON.
Figure 1: Fusarium Risk Assessment Tool screenshot of predicted risk for April 11, 2024 www.wheatscab.psu.edu
Figure 2: Fusarium Risk Assessment Tool screenshot of predicted risk for April 11, 2024 6 day outlook www.wheatscab.psu.edu
Figure 3: 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.