Soybean South :: From the Editor

 - INSECT CONTROL -

Fungicide/Insecticide
Tankmix Pays Off

 
Simultaneous applications have been shown to increase and
preserve soybean yields and seed quality.

By Carroll Smith

 
Increase soybean yields and the preservation of seed quality appear to be the goals behind field work involving simultaneous fungicide and insecticide applications done by Trey Koger, Syngenta crop specialist, for the past several years.

“As far as the fungicide, we have identified through research and demonstrations that the application of a strobi fungicide at the R3 growth stage consistently shows a yield increase and a positive net return,” Koger says. “Today, about a 65 or higher percentage of Mid-South soybean acres get that application. It’s pretty much become a standard practice.”

The next question, which has sparked debate in some cases, is whether to add an insecticide to the R3 fungicide application.

Koger says that if there are no insects in the field, especially in early planted beans, then the insecticide application is not warranted. If there is an insect identified at threshold levels, then an insecticide would go out with the fungicide. However, what about the scenario in which insects are present in the field, but none of them are at threshold levels?

Complex present, no thresholds

“Many times, a number of different insect species are out there, but not one of them is at threshold,” he says. “That is where we get into a debate. A lot of people, including some crop consultants, note that there are a number of insect species present and have been in the field for a while, and, although none of them is at threshold, there are enough insects out there that are causing some level of damage.

“Based on that situation and the fact that a farmer is already going across the field with a fungicide application, it might be a good idea to apply a fungicide/insecticide tankmix,” Koger adds.

“Typically, when we do that, it cleans out the insects, and we realize a consistent positive net return.”

Koger notes that a fungicide usually goes out in mid-July on April-planted beans, depending on the weather, maturity stage of the crop, the variety and whether the beans are irrigated or non-irrigated. If a fungicide application is warranted at that time and an insect complex is infesting the field, then a fungicide/insecticide application may come into play. If there are any stink bugs out there at this time, the application can take them out, too.

Later growth stage applications

One thing to remember, he says, is that based on years of work done by entomologists, stink bug numbers typically don’t start climbing until early August. In the Mid- South, the stink bug complex usually is made up of greens, Southern greens and browns.

Therefore, the R3 insecticide application would not have enough residual to take care of this population, which is infamous for reducing seed quality. With that in mind, Koger discusses data he collected based on making just a fungicide application at R5 to R6 and making a fungicide/insecticide tankmix application during these later growth stages.

“There was a lot of insect pressure in the field, but we just put out a fungicide,” he says. “We didn’t control the insects, so, in some cases, the seed damage was in the 30 percent range at harvest. Where we added an insecticide to the late R5 fungicide application, we were able to control the stink bugs, and the damage was minimal – two percent or less.

“The purpose of the late fungicide application is to control seed decay,” Koger says. “When rainy weather follows at that time, we have been able to consistently improve seed quality with a late fungicide/insecticide tankmix application.”

The type of insecticide used in the tankmix depends on the insect complex that is present, he explains.

“A lot of times we will use a pyrethroid,” Koger says. “Depending on the insect complex, we will put out a mixture of products such as a pyrethroid and a neonicotinoid like Endigo or Leverage, especially if redbanded stink bugs show up.”

Put simply, according to Koger, the R3 fungicide/insecticide application typically increases yields, and the R5 fungicide/insecticide application is made to preserve soybean yield and seed quality.