Alyssa K. Betts, Extension Field Crops Pathologist; akoehler@udel.edu
Most wheat flowering has wrapped up. If you have fields that are still finishing flowering, we are currently tracking at high risk for susceptible varieties (Figure 1). In barley, we are reaching the point where symptoms of FHB may be visible (Figure 2). For wheat, FHB symptoms are usually visible 18-24 days after the start of flowering. Heads with FHB will have bleached florets or bleached sections of the head and may have pink growth on spikelets. Glume blotch may also be present, but typically has more of a grey appearance. Before heads begin to dry down, it can be informative to walk the field and get a sense of how much FHB you are seeing to plan accordingly for harvest. You can follow these steps to assess the severity of FHB present in your field.
- For every 10 acres of field, randomly select one spot to survey.
- Keeping your line of sight forward above the wheat heads, walk 40-50 yards and randomly pick 10-20 heads to look at. You can keep them on the plant or detach and place into a bag. (Try not to look down until you have a handful of heads, looking down may bias 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). You can use the scale included to help calibrate your eye.
- 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% overall FHB severity)
Higher levels of FHB are typically associated with elevated levels of the mycotoxin deoxynivalenol (DON) and potential issues with yield and test weight. 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 harvested as early as possible. You can increase combine fan speeds and shutter openings to blow out the smaller, shriveled kernels. These kernels usually have the highest mycotoxin contamination, and their removal can help reduce DON levels.
Figure 1. FHB Risk Model for very susceptible varieties May 16, 2024
Figure 2. Symptoms of FHB visible on malting barley
