Fungicide Use in Corn
Fungicide manufacturers are also moving into promoting a V4-V8 timed fungicide application in corn, which is a time when foliar disease pressure is usually quite light. Again, for 2012, Syngenta reported a six- to eight-bushel yield improvement when application was done at this early timing.
PHOTO COURTESY OF UNIVERSITY OF ILLINOISGray leaf spot is the main consideration for applying a fungicide throughout the Corn Belt. A large amount of disease reduces plant photosynthesis. As for this early fungicide timing, Bradley isn’t sold on the idea, and if an ag retailer is going to sell a farmer on trying an application at this stage then it should be done in a trial situation with treated and untreated corn next to each other in a field, he suggested.
“My take on a V6 application is that there really is not much level of disease out there at that time, and a V6 application is not going to give protection throughout the entire season. So, I think the verdict is still out a little on those V6 applications.”
DuPont Pioneer research results, as provided by company agronomists on the company’s website, provide insight into what its agronomists have determined about fungicide applications on corn. Results seem to coincide with Bradley in that a fungicide application should not arbitrarily be done every year on every field.
A summary of bullet points from various DuPont Pioneer research include:
- The yield advantage with a foliar fungicide application was the greatest for hybrids highly susceptible to gray leaf spot and at sites with significant disease pressure.
- The average yield response (to using) a foliar fungicide application was greater with practices that favor high levels of residue such as corn-following-corn, no-till and strip-till.
- Factors that affect the fungicide (use) decision include disease history in the field, previous crop, tillage practices, hybrid resistance, hybrid maturity, planting date, yield potential, grain price and weather patterns.
- Fungicide application is the sole management strategy available to growers after planting.
- Scouting fields for disease as well as understanding previous cropping history and hybrid disease resistance packages can help for making the right choice when deciding whether or not to apply a foliar fungicide.
- For trials conducted between 1999 and 2007, corn yield increased an average of 7.9 bushels per acre across 345 trials in response to a foliar fungicide application.
- Tank-mixing with a postemergence herbicide application applied at V5 to V6 is a convenient, low-cost way to apply a fungicide; however, most fungal diseases are not present until later in the growing season.
- Research thus far has generally not shown a cost-effective yield benefit to early fungicide applications, either alone or in conjunction with a post-tasseling application.
Bradley’s recommendation continues to be for making a late-season fungicide application based on scouting. “For hybrids that are susceptible to moderately susceptible, consider a fungicide application when disease is present on the third leaf below the ear or higher on half of the plants in the field,” he said.
Bradley continued, “We are not talking about a certain level of disease or a certain level of severity. We are talking about where the disease is on the plant and how many plants are affected prior to tassel, with the idea being that if there is disease present on that third leaf below the ear on half the plants then disease will develop into levels that will be damaging to yields.”
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