BY: DARCY TELENKO (Purdue University Extension)
Wheat harvest has begun in Southern Indiana. Fusarium head blight (FHB) or scab is one of the most important diseases of wheat and most challenging to prevent. In addition, FHB infection can cause the production of a mycotoxin called deoxynivalenol (DON or vomitoxin). The environmental conditions have been extremely conducive to FHB development and it is not surprising that I have started to receive reports about issues with FHB and DON contamination. Our research sites in both West Lafayette and Vincennes have high levels of FHB develop in our non-treated susceptible variety checks and initial DON testing was at 7 ppm.
Fusarium head blight management is difficult and requires an integrated approach. This includes selection of varieties with moderate resistance and timely fungicide application at flowering. We are now past implementing either of these management options, but these are important to remember for next year. In addition, it will be important to assess your fields this season to determine if you have FHB. FHB can cause direct yield loss creating seeds that are shriveled and have a rough, sunken appearance to complete head loss (which I have already seen in multiple fields around the state). FHB infection can also reduce seed quality and feeding value of the grain due to the risk of mycotoxin (DON/vomitoxin) production in infected seed.
The question now is “I have scab in my field what do I need do?” Here’s a short list.
- Document the issues in each field, so you have records for making decisions on future disease management. FHB is easy to see when the head is still green – it will be much more difficult to rate as the heads reach maturity. See images of FHB in the head both at green and more mature stages. You might be able to see the pink salmon sporulation and/or purple-black fruiting bodies on mature heads (Figure 1). In addition, it is good to note during the season what management tools were attempted – spray date and growth stage of crop, was there variability in the growth stages, weather conditions after fungicide applications. These all can play a role in effective disease management.
Figure 1. Wheat spikes showing bleached florets affected by scab. Salmon to pink sporulation may be visible and can help confirm once the spikes have reached maturity (pink arrows). Dark purplish-black fruiting bodies can also occur mature wheat heads (black arrows).
- Harvest fields with lowest disease first; adjust combine settings to blow out the smaller, shriveled kernels and chaff; and separate loads from healthy and disease fields. Mycotoxin contamination is usually the highest in the more heavily disease kernels and if they can be removed that would help reduced mycotoxin level.
- Test for DON levels in both kernel and straw before feeding to livestock. Scabby kernels do not always indicate high DON and vice versa. It is important to test and know what your DON numbers are in your grain, even if you don’t see a high level of disease. Straw can also contain DON. DO NOT use straw for bedding or feed from fields with high level of scab.
- Understand your elevators inspection and dockage procedures (each one can have a different practice). Levels of DON greater than 2 ppm may lead to price discounts.
- It is not recommended to store grain from field with high levels of scab – accumulation of DON and other mycotoxins can continue in stored grain. Suspect grain, if stored, should be dried to 5% moisture as soon as possible after harvest and kept separate from the good quality grain.
- Planting seed from fields that had moderate to heavy scab is not advisable. The infected seed will have low germination and poor vigor resulting in a thin stand. If going to use this seed, it should be cleaned thoroughly to remove the scabby seeds, and a fungicide seed treatment would be advised to protect germination and reduce seedling blight.
The next question “Why was is it so bad? I followed the guidelines applied my fungicide at flowering but we still have poor control.”
Here’s a few of my observations:
- Highly favorable environmental conditions for Fusarium head blight (FHB)/scab occurred all spring.
- Many wheat varieties have moderate resistance that help can reduce the risk of sever disease, and fungicides can help suppress the development, but this may only provide about 50% suppression. Therefore, even with the best management programs in place the extremely favorable conditions for FHB have led to high levels of infection this season.
- There was extremely variable growth in individual fields this year – plants ranged from boot to full flower when trying to make a decision on fungicide timing. In addition, fungicides may only provide partial suppression of FHB and timing is a significant issue for obtaining moderate levels of control.
- Frequent rains not only complicated planting, but any and every other trip across the field. Rain events closely following fungicide application may have diluted or washed off applications further reducing expected efficacy.
Additional references:
US Wheat and Barley Scab Initiative https://scabusa.org/
Cowger, C., and Arellano, C. 2013. Fusarium graminearum infection and deoxynivalenol concentrations during development of wheat spikes. Phytopathology 103:460-471. https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-03-12-0054-R
De Wolf, E. 2019. Fusarium head blight. https://www.bookstore.ksre.ksu.edu/pubs/MF3458.pdf
Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Dis. 95:1448-1457. https://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-04-11-0309
Wise, K. et al. 2015. Diseases of Wheat: Fusarium Head Blight (Head Scab) https://www.extension.purdue.edu/extmedia/BP/BP-33-W.pdf