Focus on Fungicides

April 29, 2011 10:21 PM

Farm Journal Test Plots Examine Application Timing

The benefits of using fungicide in corn aren’t always clear-cut and easy to measure. Field research conducted in 2010 in the Farm Journal Test Plots by Ken Ferrie and Missy Bauer, Farm Journal Field Agronomists, set out to get a handle on application timing.

One of the questions the agronomists wanted to answer was how an early season fungicide treatment in corn at the V5 growth stage would compare to an application at the R1 stage, which is the traditional timing for fungicide applications.

A second question was whether there was any benefit to applying fungicides at both times, compared with making one application at one or the other timing.

Bauer, who is based in southern Michigan, explains that yield potential in corn begins at around the V5 growth stage, so some manufacturers recommend applying a fungicide at that point to provide what the chemical industry calls a plant health response. Fungicide applications made at the R1 corn growth stage are used to shut down disease pressure.

For the studies, she evaluated the performance of Syngenta Quadris and Quilt Xcel fungicides and BASF Headline and Headline AMP fungicides.

All products were applied at labeled rates in southern Michigan irrigated fields owned by North Concord Farms in two different rotational scenarios: corn on corn and corn after soybeans. The test plots ranged in size from 25 acres to 50 acres and each contained one 105-day hybrid and one 106-day hybrid, based on comparative relative maturities. Both hybrids offered low to moderate susceptibility, depending on the disease specified. Each trial was replicated three times. No comparative studies were conducted between the products.

Yearly rainfall levels were average for the 2010 season, but disease pressure in the fields, specifically northern corn leaf blight, was at the heaviest level Bauer has ever experienced in the area.

When Bauer evaluates fungicide treatments, aside from hybrid response, she typically finds that the best response is in irrigated fields that are planted into corn-on-corn rotations.

Ferrie agrees with Bauer, noting that his 2010 fungicide studies also were based on the treatment timing of R1 and V5 but were made only in non-irrigated fields with corn on corn and corn after soybeans.

"High disease pressure from old corn residue, extended periods of leaf wetness and adequate soil moisture allow disease to proliferate," Bauer says. "Agronomically, that’s a tough scenario that should help fungicides have the most positive response."

In ranking the responses to fungicides in Bauer’s three other agronomic scenarios, corn on corn in nonirrigated fields is second best; irrigated corn grown after soybeans is third; and the fourth best scenario is corn grown after soybeans.

"It’s important to not only consider the hybrid disease ratings but also the cultural practices and environment," she explains. "You must respect the disease triangle."

Key take-aways.

Fungicide treatments that were made at V5 were economically advantageous in Bauer’s plots 75% of the time and 100% of the time in applications made at the R1 timing (see charts below).

"Another take-away was that there was a slight additive effect observed," Bauer reports. "Using both application timings was better than using either alone in the corn–soybean rotation in terms of yield, but there wasn’t an economical benefit."

irrigated notill corn

Bauer says she believes that the unusually heavy infestation of northern corn leaf blight late in the season contributed to the positive response at the R1 timing.

Plus, she explains: "Perhaps there is a plant health response at the V5 timing since we had little disease pressure at that point."

Normalized Difference Vegetation Index (NDVI) maps, which measure plant growth, were used in the Michigan fields to assess their relative vegetation biomass and vigor. NDVI measurements help agronomists detect variations and less-than-desirable plant health within a field. BASF and Syngenta provided the financial resources for the use of this technology. The effects of the fungicide treatments were evident in the NDVI images, which showed greener vegetation where fungicides were applied.

R1 rules.

In Ferrie’s plot studies, conducted in central Illinois, the R1 treatment also yielded the best results.

"Our R1 treatments were more consistent in providing an economically viable yield response compared with the combined application of both R1 and V5 treatments," he says.

Ferrie says heat stress between the time of pollination and black layer may have contributed to the less-than-favorable test results with the combination of the V5 and R1 treatments.

He adds that the plots that received the V5 and R1 combination looked cleaner than either treatment alone but did not provide an economic return.

"I do wonder if we wouldn’t have had a better response if we’d had a longer, more traditional fill period," Ferrie says, noting that the corn harvest in his area concluded nearly a month earlier than usual.

Ferrie also cautions growers who might want to use a V5 treatment in lieu of an R1 treatment. "Our trials say that would be a mistake economically," he says.

At the same time, Ferrie says there are a few scenarios in which a V5 treatment alone may be a viable option.

"If I have a grower who has never sprayed a fungicide before and has never scouted his fields before, I would say that the V5 application timing is OK starting out, though not ideal," he explains. "Or if the grower doesn’t have access to an aerial or high-clearance application to make an R1 treatment, or his fields are next to ball fields or power lines, making a later application more difficult, then a single V5 treatment may be a viable option."

Bauer encourages farmers to conduct their own plot research, taking into consideration hybrid susceptibility, to see what level of benefit fungicides provide when applications are made at the V5 or R1 timing.

"I especially encourage in-field tests if farmers are growing irrigated, corn on corn," she says.

Thank You to Our Test Plots Partners

Each Farm Journal Test Plot is a cooperative effort. Thanks go to: BASF and Yvette Fetterly; Syngenta and Josh Louder; Apache Sprayer and Charlie May; Illini Sprayer, Mike Flatt and Luke Nessa; North Concord Farms; Bob Kuntz; B&M Crop Consulting and Bill Bauer; Crop-Tech Consulting, Brad Beutke and Isaac Ferrie.



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