Project evaluates pest management tools used in soybeans

Frances Gould  |  8/14/2015 12:37:21 AM

LSU AgCenter entomologists are evaluating programs that crop consultants and farmers use to control pests in soybeans across the state.

The project evaluates the tools growers use and compares them to new approaches and new tools that either are available or will be in the near future, said LSU AgCenter entomologist David Kerns.

"A portion of what we do is to evaluate old and new insecticides for their ability to manage soybean insect pests," he said. "First, we simply want to know how well they work for particular pests and, second, how to use them in an integrated system to maximize profits.

"There is a large complex of insects that affect soybeans," he said. "We look at everything that we come in contact with in that given year."

For instance, after a particularly cold winter, redbanded stinkbugs will not be numerous, and the stinkbug complex will shift to brown and green stink bugs.

"In 2014, fall armyworms were a big problem in many areas," he said. "The problem was so bad that one of my colleagues called it an ’armyworm-a-geddon.’ As applied scientists, we try to be flexible to what questions the growers and consultants have at a given time and what research to conduct to help address those questions."

Another factor that affects insecticide choice is the development of resistance. An insect’s susceptibility to a particular insecticide may change over time. For instance, Kerns and other entomologists have continued a program to monitor bollworms for susceptibility to pyrethroids. This program is the longest-running of its type in the nation, having been started in the 1980s.

"We are continuing to monitor resistance in bollworms today," Kerns said. Some years, resistance is high while others are moderate. Data generated from this monitoring helps consultants and farmers decide which insecticides may or may not work under a particular situation.

Kerns said another goal is to determine action thresholds that indicate when farmers should apply insecticides to prevent economic injury. One project that’s been revisited for the past couple of years is the economic threshold for bollworms in soybeans.

"There was an action threshold that was developed years ago. And back when it was developed, a lot of the soybeans were different from what we plant today," he said. "Back then, we were planting later-maturing soybeans – a lot of Group 6s. Now we are growing Group 4s and early Group 5s."

The question that Kerns and other scientists want to answer is whether the action thresholds are still valid because the plants mature at different times.

"A group of us in the Midsouth – Louisiana, Mississippi, Arkansas and Tennessee – have a joint effort to try to redefine this threshold," Kerns said.

The project involves releasing moths into cages, then sampling them to determine the number of larvae. But a number of factors could negatively affect the data, such as heavy rain and high wind or an infestation of natural enemies that may get into the cages and eat the eggs and the larvae.

"It’s possible that we may be putting the moths out at the wrong time, where they may be getting heat-stressed," he said. "Based on the data we currently have, the action threshold for bollworms in soybean does not look like it will change much."

Johnny Morgan

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