Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Most wheat fields are at or shortly after anthesis. We had quite a few rain events during the flowering windows for barley and wheat, which kept us at high risk for Fusarium Head Blight (FHB). The recommended stage for fungicide application is when 50% of main tillers are flowering (yellow anthers visible) until 4-5 days after. Once wheat has flowered, symptoms of FHB are visible in 18-24 days, but cool weather can slow symptom development. Heads with FHB will have bleached florets or bleached sections of the head (Figure 1) and may have pink growth on spikelets. This year we will also have to sort out bleached florets that were from frost events prior to flowering (Figure 2). (Glume blotch may also be present, but typically has more of a grey appearance).
Figure 1. Symptoms of Fusarium Head Blight
Figure 2. Bleached florets from frost damage
You can follow these steps to assess the level of FHB present in your field.
- For every 10 acres of field, randomly select one spot to survey.
- Keeping your line of sight above the wheat heads, walk 40-50 yards and randomly pick 10-20 heads to look at on the plant or detach and place into a bag. (You don’t want to be looking down and biasing the heads you select).
- Once you have randomly collected the heads, rate the percent of each head with symptoms of FHB (bleaching or pink growth on spikelets).
- After you have recorded values for each head, determine the average percent FHB severity by dividing the sum of disease severities by the total number of heads collected.
(Ex. You rate 10 heads with severity values: 0, 10, 30, 0, 0, 20, 10, 0, 0, 0. These add up to 70. 70/10 heads = 7% FHB severity)
Higher levels of FHB are typically associated with elevated levels of DON and possible issues with yield and test weight. In colder years like this, it is possible to have delayed or lower levels of symptoms and still have DON.
- Repeat this assessment as needed to get an overall rating for the field. Fields with greater than 10% FHB severity are at higher risk for yield losses or elevated DON. Fields with elevated DON should be harvest as early as possible and you may want to consider increasing combine fan speeds and shutter openings to reduce the amount of scabby kernels harvested.