Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Wheat anthesis (flowering) is underway. Up until the rains this past weekend, we have been at low FHB risk. We are currently tracking as high risk for very susceptible varieties (Figure 1) and low-medium risk for varieties with some level of resistance (Figure 2). If you are planning for wheat fungicide application hopefully you have been scouting frequently looking for yellow anthers in the center of the wheat head (Figure 3) to signal that flowering has begun (Feekes 10.5.1). We can usually expect flowers to start showing up on wheat heads 3-5 days after full head emergence, but you may have seen a delay with the cooler weather, stretching this process out to 7-10 days. Anthers can remain attached after flowering, but become pale white. For best mycotoxin (DON) control, it is better to be at flowering or a few days beyond than to spray too early when heads are not out yet (especially those secondary tillers). Many fields are now at prime time for optimal application.
Figure 1. FHB Risk Model for very susceptible varieties May 4, 2023
Figure 2. FHB Risk Model for susceptible varieties May 4, 2023
Figure 3. Wheat at flowering (Feekes 10.5.1) with yellow anthers visible 3-4 days after heads emerge
Pythium Root Rot in Corn – Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Wet conditions around the time of planting can favor the oomycete pathogen, Pythium. Symptoms of Pythium Root Rot can include stunted, slower growing plants, to severely infected, dead plants (Figure 1). Infected plants typically have brown, rotted roots and mesocotyl (Figure 2). As root systems continue to develop, seedlings can survive mild to moderate Pythium infections, but final yield is often impacted. Unfortunately, plants that are infected early generally maintain reduced root systems throughout the season, with ears that are poorly formed (Figure 3). In some cases, infected plants may be barren with no ear formed. In trials over the past 3 seasons we have observed that yield potential of infected plants is reduced by 60% on average. Seed treatments with oomycete activity can provide some protection within 10-14 days after planting, and can be helpful for improving seedling emergence and reducing pre-emergent damping off. To date, we have recovered 14 species associated with corn in DE/MD, with Pythium graminicola being most common. Pythium species differ in optimal temperatures for growth and can have varying responses to fungicides. In lab trials, the newly launched product Vayantis is looking promising for activity across multiple species. We will be screening this seed treatment in field trials this season. The weather over the past week may be favorable for development of Pythium in corn that was planted throughout April. If you need assistance in identifying if you have Pythium in your field, contact Alyssa Koehler, akoehler@udel.edu.
Figure 1. Corn seedlings with post-emergent damping-off caused by Pythium spp.
Figure 2. Corn seedling with necrotic, brown mesocotyl following infection by a Pythium spp.
Figure 3. Photos from paired field trial of Pythium infected (top) v. healthy corn plant (bottom).