Vomitoxin management and corn fungicide decisions during pollination

Deoxynivalenol (DON), commonly referred to as vomitoxin, has become a significant problem for Ohio corn growers. What was once considered an every-ten-year problem has now become a yearly challenge in some sections of the state. DON contamination of grain is associated with Gibberella ear rot (GER), a disease caused by the fungus Fusarium graminearum. The Ohio State University Cereal Pathology Lab led by Dr. Pierce Paul has been researching and developing weather-based models to predict when weather conditions are favorable for DON contamination of corn grain. The current models predict when conditions are favorable for grain to be contaminated with at least 1 ppm DON.

DON model predictions are based on data from publicly available weather stations. The two weather variables used to make predictions are temperature and relative humidity. These conditions can vary significantly over a few miles or with changes in elevation. The current models were not developed to predict whether DON will be 2, 5, 8, or 10 ppm; they only predict whether DON will be ≥ 1 ppm, but not how much greater. 

The vomitoxin forecasting tool is part of the Crop Protection Network ’Crop Risk Tool’ available at https://connect.doit.wisc.edu/cpn-risk-tool/. From this tool, you can select the location of each field and evaluate the DON risk for the corn crop pollinating on a date specific for that field, based on weather during the 14 days prior to pollination. If risk is high, a fungicide application specifically for Gibberella ear rot and lower DON levels at harvest may be warranted if a susceptible hybrid is planted. Figures 1-3 show examples of the risk classifications and their management implications.

 
The fungus that produces DON primarily infects corn ears during pollination, when the silks are wet (R1 growth stage). While insect feeding later in the growing season can be a route for secondary infection, the risk is lower than during silking. We have been conducting hybrid resistance research, which has shown reduced DON levels when more BT insect resistance traits were present.

Effective management of DON requires the combination of multiple strategies. A model prediction can help you determine if a fungicide for DON management would be beneficial. Of the many fungicides available for corn disease management, four are now labeled for suppressing GER and DON in Ohio. Two products Proline 480 SC and Miravis Neo are traditionally labeled. Three other products have a 2(ee) label for Ohio and eleven other states. The first is Prosaro Pro 400SC at 10.3 fl oz/acre and Proline 480SC at 1.41 fl oz/ac as a tank mix. The second one is a tank mix of Delaro Complete and Proline 480SC. Three rate combinations are approved: 8 fl oz Delaro Complete plus 2.75 fl oz Proline 480SC per acre, 10 fl oz Delaro Complete plus 2.02 fl oz Proline 480SC per acre, and 12 fl oz Delaro Complete plus 1.28 fl oz Proline 480SC per acre. The third is Headline AMP at 14.4 fl oz per acre. They have shown the best results when applied when silks are still wet (early- to mid-R1). The fungicide must penetrate the canopy and reach the corn silks when they are still wet to be effective. Applications made after silks are dry and brown are considerably less effective at reducing DON, with research showing that by 11 days past full silk, DON levels were the same as when no fungicide was applied. With the variation this year in plant growth stages and some fields having replanted corn in patches, perfect timing may be hard to achieve. Your goal should be to apply fungicide when most of the field is silking but before the earliest silks turn brown. While not as effective as applying the fungicide during wet silk, the DON reduction is greater with a V18 application than a brown silk application. If weather conditions are making the fungicide application difficult, it is better to be early than late.

Hybrid resistance is crucial, even with fungicide application, in achieving low DON levels at harvest. A hybrid with partial resistance will have lower DON at harvest than a susceptible hybrid when both have received a fungicide application for DON management. Extended harvest periods allow more time for DON production, particularly if harvest is delayed by wet conditions. An additional tool is to scout fields that pollinate during high-risk times for GER and plan to harvest those fields early.  

It is important to remember that weather conditions are only one part of the disease triangle, and that all three sides of the triangle are needed for disease development, and in this case, for DON contamination to occur. The other two sides of the disease triangle are a susceptible corn hybrid and fungal spores being present at the time and growth stage when weather conditions favor infection, disease development, and toxin production. Consequently, the actual level of DON contamination will vary from field to field, depending on the susceptibility of the hybrid planted, tillage, and crop rotation, as well as weather conditions. Under favorable weather conditions, a highly susceptible hybrid planted no-till into corn stubble will likely be contaminated with DON well above 1 ppm compared to a tilled field of a moderately resistant hybrid planted after beans.   

Use predictions as one piece of information to help guide your DON management decisions. You should also consider the susceptibility of your hybrid and production practices when making management decisions. The results of the 2023, 2024, and 2025 DON hybrid resistance screening trial can be found at http://go.osu.edu/vomitoxin. This site also contains results from other corn DON research projects done at OSU. Again, when weather conditions are favorable as suggested/predicted by the models, fields of highly susceptible hybrid planted no-till after corn will likely yield grain with DON above 1 ppm compared to a tilled field of a moderately resistant hybrid planted after beans.