Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Small grains are moving right along with most barley heading and wheat approaching or just beyond flag leaf. The forecast looks dry over the next week, which is good for limiting FHB pressure. The whole region has dropped to low risk in the Fusarium Risk Tool through the weekend (Figure 1).
Figure 1. FHB Risk Model for April 29, 2021 (wheatscab.psu.edu)
Figure 2. Wheat at beginning flowering (Feekes 10.5.1) with yellow anthers at the center of the head
If you are planning for wheat fungicide application, scout frequently and apply when wheat is flowering (Feekes 10.5.1). Look for yellow anthers in the center of the wheat head to signal that flowering has begun (Figure 2). Once wheat is flowering, fungicides are most effective when applied within a 4-5 day window. Anthers can remain attached after flowering, but become a pale white. Fungicide products should be applied at the manufacturers recommended rate with nozzles that are angled 30-45° from horizontal (30 degrees is better than 45). Nozzles angled both forward and backward or twinjet nozzles that spray in two directions give better contact with the head and increase fungicide efficacy. For ground sprays, fungicides should be applied in at least 10-15 gallons of water per acre; aerial applications are recommended at 5 gallons per acre.
In addition to FHB, we often see foliar diseases including tan spot and glume blotch (Parastagonospora nodorum) as we get into May. Glume blotch, also called Septoria nodorum blotch (SNB) when on foliage, has symptoms of small brown lesions with a yellow halo, as the lesion expands this is often in a “cat eye” shape (Figure 3). 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.
Figure 3. Lesions of glume blotch (Septoria nodorum blotch) on wheat