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| Purdue pathologist warns of fungicide yield boost claims |
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By DOUG GRAVES
Ohio Correspondent LAFAYETTE, In. — Farmers who apply fungicide to corn and soybeans because they believe the chemical boosts yields could be treating their crops with little more than a placebo.
That may come as a surprise to many who have used fungicide applications their entire life, but Greg Shaner, Purdue University professor of botany and plant pathology, is convinced the data is inconclusive as to whether fungicide is really effective. And his two-year trials may prove it.
“It’s almost a coin toss as to whether producers will get their money back in increased crop yields from fungicide treatments,” Shaner said. “Producers probably should only use a fungicide if they have reason to think they will have disease pressure.”
Fungicides are used to control such fungal diseases as gray leaf spot and northern corn leaf blight in corn, and Asian Soybean Rust and frogeye leaf spot in soybeans. The diseases attack leaves – plant parts that are critical in normal development and grain production. Fungicide applications usually are made at the onset of disease.
In recent years, some chemical manufacturers have claimed fungicide applications enhance corn and soybean yields even when no disease is present. Shaner and other Purdue researchers have not been able to either prove or disprove those claims. Results from the test trails were mixed among and between corn and soybean plots, Shaner said.
“With corn, the Purdue trials indicate about a 50-50 positive to neutral yield response following fungicide treatments,” Shaner said. “In soybeans, in some cases, there’s a yield response. That is, the yield increase is more than enough to pay for the fungicide application.”
Fungicide treatments run $18-$23 per acre, including application costs.
“When you look at the data from a lot of different trials from many states, the yield response may be as high as 20 bushels per acre, but it may be a fraction of a bushel,” Shaner said. “On the negative side, there have been instances where yields have been six or seven bushels per acre lower.”
According to Shaner, farmers who plan to treat their 2008 crops with fungicide likely already have purchased product or hired professionals to do the work.
“Most fungicide on corn is going on by aerial application because there aren’t that many ground rigs that can get over the top of tasseled corn,” he said. “We don’t have that many aerial applicators in the state, so what I think happens is that contracts to treat fields are being set up in February.
“Obviously, at that point, a grower hasn’t got a clue what the disease pressure is going to be the following summer.”
Shaner encourages producers to carefully weigh their fungicide use plans against the disease resistance traits of the corn and soybean hybrids they plant. Seasonal weather patterns also are a factor.
“If a hybrid has pretty good resistance, then I think the chance it will benefit from the fungicide isn’t very great,” Shaner said.
“Conversely, if a hybrid or variety is susceptible to one or more leaf diseases and weather is favorable for disease development, then it is more likely that a fungicide application will be economically justified.
“This whole business of fungicides on corn and beans is pretty new. There’s a lot that needs to be learned about decision aids, thresholds and weather-based disease forecasts that can help growers decide if a fungicide would be valuable or not.”
Shaner teaches three courses at Purdue University: Plant Disease Epidemiology, Genetics of Host-Parasite Interaction and Fundamentals of Plant Classification. He also instructs in two team-taught courses: Principles of Plant Pathology and Plant Disease Management.
This farm news was published in the April 9, 2008 issue of the Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee. |
| 4/9/2008 |
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