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Late fungicide might preserve soy quality

Mississippi researchers are taking a close look at the use of a late fungicide application on soybeans to preserve seed quality.

For the past several years and particularly the last two years, seed quality has been a tremendous problem across the state, resulting in significant market loss, according to Trey Koger, the state’s Extension soybean specialist. “Hands down, seed quality has been our biggest production issue.”

In 2009, Mississippi soybean producers lost almost 30 percent of the overall value of the crop to seed quality issues, Koger said. “We had 2.2 million acres, and the farm gate value was about $440 million. If we hadn’t had all the significant losses, our soybean crop value would have been a little over $600 million. Those were astronomical losses last year.”

In 2008, Koger says, Mississippi soybean producers lost about 15 percent of the value of the crop to seed quality damage, specifically Phomopsis seed decay, due to wet weather preceding harvest.

To address some of the concerns, researchers at MSU are studying the effectiveness of late fungicide applications, such as a strobilurin (i.e. Quadris or Headline), at R-5 to R-5.5 “to preserve seed quality. A lot of times, we’re going across the field anyway with an insecticide to control stink bugs or bollworms,” Koger said.

How a fungicide performs with respect to seed quality depends largely upon the weather following the application, the research says. For example, a fungicide is probably not going to help soybeans when an application is followed by eight weeks of wet weather while soybeans are waiting in a field ready for harvest. This occurred across much of the Mid-South in 2009.

On the other extreme, “you can apply a fungicide to preserve seed quality, and if you get beautiful weather from that point forward, you might not have needed it. In that case, it’s kind of like insurance. We hope we don’t need it. But if we do need it, we got it.”

The benefit from a fungicide is greatest, noted Koger, when there “are a few days of wet weather” around harvest.

The trials, being conducted by Koger and Tom Allen, plant pathologist at Delta Research and Extension Center, also indicated an added seed quality benefit when an insecticide and fungicide were used together at R-5 to R-5.5, and stink bugs were present, according to Koger.

“Stink bugs can cause damage to the seed, so if we use a fungicide, but don’t control the stink bugs, we can still get a seed quality problem. If we do control the stink bugs, and apply a fungicide, we can almost eliminate some of the seed quality problems we have. We can have a beautiful soybean crop.”

In fact, research indicated damage numbers of 2 percent on fungicide plus insecticide treated soybean plots when stink bugs were present. Damage was as high as 60 percent in untreated plots.

When only a fungicide or insecticide was applied alone, “our damage was 35 percent to 40 percent. So the fungicide and insecticide complement one another. You have to control the insects, and you have to use a fungicide to preserve seed quality.”

The trials also indicated that a late fungicide did not provide a seed quality benefit when there was little or no stink bug pressure, and harvest was completed in a timely manner. “We applied the treatments, got all the plots harvested before it ever started raining, and the quality was exceptional,” Allen noted. “Even the untreated checks had 1 percent to 2 percent damage.”

A trial in Starkville, Miss., best illustrates the disastrous effects of weather, no matter what the treatments. “We didn’t have much stink bug pressure, applied all the fungicide/insecticide treatments, and we had eight weeks of wet weather, six weeks of which came after the beans were ready to cut,” Koger said. “Everything was 80 percent to 100 percent damage.”

Other important factors include combine capacity and grain storage capability, according to Koger. “Our growers with sufficient combine and bin capacity can get across acres, and they can store, blend and dry down the crop. That helps tremendously versus the grower who doesn’t have adequate capacity. They could have a crop that’s ready to cut, but the elevator won’t take them because the moisture is high and they sit in the field and get more rain on them and they rot.”

Quality is typically worse in dryland soybeans, according to Koger. “The dryland crop is going through a wide range of stressors throughout the season, while our irrigated crop is not. The southern part of the state usually sustains more seed damage than the northern part of the state. As a general rule, we have more dryland acres in the south than in the north.

“However, 2009 did not discriminate between irrigated and non-irrigated acres with most soybean acreage across the state enduring the disastrous effect of several weeks of continuous rain just when a majority of the soybean crop was reaching maturity. We all hope we never see a harvest season like 2009 again.”


TAGS: Soybean
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