Fungicide Use in Corn

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The majority of university plant pathologists continue to contend that foliar fungicide applications to corn should be driven by the hybrid’s resistance to foliar diseases, amount of disease present on the corn leaves, and risk factors for the disease pressure increasing after the tasseling (VT) stage.

On the other side of the question of whether a fungicide should be applied to corn are the crop protection manufacturers of fungicides. The argument of pro and con about fungicide use between university researchers and fungicide companies has continued for years, and both sides appear to be armed with research data that supports their arguments.

Carl Bradley, Department of Crop Science, University of Illinois, in speaking to attendees of the University of Missouri Crop Management Conference, said he looks at fungicide use as a tool that should increase yields enough to more than pay for the cost of the fungicide and application. In this day of higher corn prices, that increase in yield doesn’t have to be much of an increase compared to a few years ago when corn prices were much lower.

CONSIDER PROFITABILITY

“For foliar disease control and yield response, we tend to see more consistent profitability when fungicides are applied because of a disease threat,” Bradley said.

From Illinois research run the last five years, he said, “Less than one-half of the time we would have been profitable when spraying fields that had a relatively low level of disease.” These results are most applicable when the hybrid is resistant to disease and especially gray leaf spot.

The main discussion about fungicide use on corn is for an application between the VT and brown silk (R2) stage late in the growing season.

If a corn field is sprayed with a foliar fungicide and there is little or no disease present, but a yield bump occurs, then the fungicide is having an affect other than disease control on the plant. “There are some other factors that can occur with these fungicides that are not related to disease control,” Bradley said.

Crop protection companies and ag retailers have been able to convince a growing percentage of corn growers to use a fungicide application because there have been yield bumps unrelated to disease. BASF was the first company to heavily promote the VT to R2 fungicide application based on protecting “plant health.”

YIELD BUMP

Last fall BASF came out with new study results it claims showcase the plant health benefits of fungicides and its F500 active ingredient component. Protecting a corn plant’s efficient photosynthesis, according to the research, drives increased yields.

PHOTO COURTESY OF BASFAerial application has been the main application technique for applying a fungicide between the VT and R2 stage of corn growth. “Photosynthesis is the driving engine for energy production in plants,” said Jennifer Holland, Ph.D., technical market specialist, BASF. “An increase in net photosynthesis means the plant has the ability to create more energy for use in the reproductive stages, which can lead to higher yield potential.”

There are “three pillars of plant health,” which can be affected by a fungicide, and the three are disease control, growth efficiency and stress tolerance.

Growth efficiency relates to benefiting the corn plant’s utilization of nitrogen fertilizer, and stress tolerance means the plant won’t be weakened and lower photosynthesis, according to Holland.

BASF reported, “In the study, conducted under water-stressed conditions, plants treated with a fungicide were nearly 30 percent more efficient at net photosynthesis than the untreated plants. The fungicide-treated plants were able to handle stress better than untreated plants, which can lead to higher yield potential.”

DROUGHT TOLERANCE

Syngenta also recently reported that corn treated with its fungicide, Quilt Xcel, during 2012 better tolerated drought. The company provided its version of what is going on to help the plant tolerate the heat and lack of water. The fungicide was “shown to reduce stomatal conductance, or the passing of water through the plant stomates, the natural openings in plants that allow exchange of water and gasses. This improves a plant’s water use efficiency. As plants regulate water loss more efficiently, soil moisture is conserved and plants are better equipped to tolerate periods of hot, dry weather.”

Syngenta also said its long-term evaluation of corn receiving the late-season fungicide application shows plants stay green longer, have corn ears that grow bigger, experience extended grain fill and have stronger stalks.     

In fields infected with gray leaf spot or southern rust, Bradley has also looked at a late-season fungicide application reducing stalk rot. Again, in general, if disease pressure justified a fungicide application, then stalk rot problems could be reduced compared to untreated disease infected corn plants. But hybrids resistant to the diseases were less likely to show much improvement in stalk quality, he explained to the Crop Management Conference crowd in Columbia, Mo.

EARLY-SEASON APPLICATION

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.”

OTHER RESULTS

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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