Growers looking at applying fungicides to row crops should do so, but do so cautiously and sparingly, said a Purdue University expert.

Fungicides have been used for years by fruit and vegetable growers, but not much is known about the payoffs of fungicide application for corn and soybeans.

Growers that decide to apply a fungicide and want to test it out for themselves should choose portions of fields to spray at random, said Greg Shaner, Purdue Extension crop specialist. This gives a better indication of yield results from spraying than intentionally choosing the area to be sprayed, because there may be a tendency to treat an area that historically yields better anyway.

When analyzing yield results, remember other factors should be considered such as soil type and moisture level, as well as the fungicide treatment, Shaner said.

Timing is critical for fungicide application. Fungicides work better as preventatives than as curatives, Shaner said. It is important to spray a crop just at the onset of disease as most fungicides only remain effective for three weeks. This means that if a fungicide is applied too early, it will not still be there when needed. If a fungicide is applied to late, it will not stop the disease.

“A general guideline for corn is to make the first application when there are no more than a couple lesions on lower leafs of about half the plants in a corn field,” Shaner said.

“We have the threat of soybean rust, but it hasn’t yet been a problem in the Midwest,” Shaner said. “If it does appear during the summer, then we have got a definite problem and we will need to use fungicides.”

For ground application of fungicides, use 10 gallons per acre. Research at Purdue suggests 15 gallons per acre gives better coverage and canopy penetration than 10 gallons per acre. Five gallons per acre is the standard for aerial application, but a couple of fungicides can be applied at 2 gallons per acre.

Research is being conducted with electro-static technology, which requires only 1 gallon per acre, but is not yet commercially available. As the fungicide droplets emerge from the spray nozzles, they are given an electrical charge, causing them to be attracted to the foliage. But because the droplets have the same charge, they repel each other and disperse in a more uniform pattern.

“This summer we are working with an aerial applicator to apply fungicides on corn and soybean fields at three different increments—5, 2 and 1 gallon per acre,” Shaner said. “Our goal is to collect data on the amount of disease control, yield difference and bottom line resulting from applying a fungicide to both corn and soybeans.”

In the weeks following the fungicide application, sprayed fields and unsprayed fields will be compared for disease control. Yield will also be compared after harvest.

From our aerial application trials we will learn if the decreased volume and smaller droplets, provide the same disease control and yield benefit as conventional aerial application, Shaner said.

He explained that some manufacturers believe fungicides have general plant health benefits, meaning that even though there may be no real foliar disease problem or need to control anything there are yield responses.

The fungicides are not actually controlling the disease problem, but rather giving the soybean plant a boost, Shaner said.

“It’s possible that some of the late season soybean diseases, such as pod and stem blight and anthracnose—diseases, which are not evident until the beans are maturing and starting to drop their leaves—may be doing more damage than we realized and fungicides are controlling them,” Shaner said.

Unlike soybeans, spraying corn with a fungicide is more for disease control, Shaner said. But that is an area that still needs more research.

Shaner does know that in determining whether or not to apply a fungicide to a field, plant susceptibility must be taken into account.

“Among all the corn hybrids that are available, there is quite a range in resistance to leaf diseases. Some have pretty good resistance, some not so good resistance and some are pretty susceptible,” Shaner said. “We anticipate that you would see a response and an economic return if you spray a hybrid that is fairly susceptible.”

In spraying a fairly susceptible hybrid, the leaf tissue is protected and so is the yield.