Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Wheat anthesis (flowering) is wrapping up. If you have fields that are still flowering, we are currently tracking at high risk for very susceptible (Figure 1) and medium-high risk for varieties with some level of resistance (Figure 2) in the risk model. We should have remained at low risk for most barley fields. We are just reaching the point where symptoms in barley may start to become visible (Figure 3). In my scouting so far, I have seen very limited FHB in barley. Once wheat has flowered, symptoms of FHB are usually 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 and may have pink growth on spikelets. Glume blotch may also be present, but typically has more of a grey appearance. 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 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. (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 DON and possible 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 and you may want to consider increasing combine fan speeds and shutter openings to reduce the amount of scabby kernels harvested.
Figure 1. FHB Risk Model for very susceptible varieties May 11, 2023 (wheatscab.psu.edu)
Figure 2. FHB Risk Model for susceptible varieties May 11, 2023 (wheatscab.psu.edu)
Figure 3. Symptoms of FHB starting to become visible on malting barley (Photo: A. Koehler)
