Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Across much of the region, wheat is now at the 10.0-10.4 growth stage with heading well underway. Last week when many plants were in boot stage, we were hit with multiple cold nights that caused leaf discoloration and resulted in some heads not emerging properly (Figure 1).
Figure 1. A normal emerging head (left). Head trapped in the boot due to freeze at the boot stage (center). Head that was trapped and did not emerge properly (right).
Foliar diseases including tan spot and glume blotch (Parastagonospora nodorum) have begun to show up this week. Glume blotch, also called Septoria nodorum blotch when on foliage, has symptoms of small brown lesions with a yellow halo; as the lesion expands this is often in “cat eye” shape (Figure 2). Since leaf blotch precedes glume blotch, lesions high in the canopy and on the flag leaf can indicate an elevated risk for glume blotch. Tan spot also has brown lesions with a yellow halo, but these tend to have more of a diamond shape. A fungicide application to control FHB at flowering will often help control many of these foliar diseases. With the recent rains and more in the forecast, FHB risk has increased to a moderate/high level across the state and eastern shore (Figure 3). If applying fungicides for FHB, these should be targeted when at least 50% of heads across the field are flowering and showing yellow anthers (Figure 4).
Figure 2. Lesions of glume blotch (Septoria nodorum blotch) on wheat
Figure 3. FHB Risk Model for April 30, 2020 (wheatscab.psu.edu)
Figure 4. Wheat at beginning flowering (Feekes 10.5.1) with yellow anthers at the center of the head