Johnny Morgan, Kerns, David L.
BATON ROUGE, La. – LSU AgCenter entomologists are evaluating integrated pest management programs that crop consultants and farmers use to control pests in soybeans across the state.
The project evaluates the tools growers are currently using and compares them to new approaches and new tools that might either be currently available or that may be available 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 utilize them in an integrated system to maximize profits.
“There is a large complex of insects that affect soybeans,” he said. “We really 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. Under those circumstances, some research projects from redbanded to brown and green stinkbugs.
“In 2014, fall armyworms were a big problem in many areas,” he said. “The problem was so bad in some areas that one of my extension 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 we may 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, bollworms in Louisiana are notorious for having resistance to pyrethroid insecticides.
Kerns, along with other entomologists in the state, has 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 investigate action thresholds to determine when farmers should apply insecticides to prevent economic injury.
One project that’s been revisited for the past couple of years is the economic thresholds of corn earworm or bollworms in soybeans.
“There was a 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 tend to be growing group 4s and early group 5s.”
The question that Kerns and other scientists want to answer is whether the 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. “It’s a lot of work because it takes a lot of data to develop a new threshold.”
The project involves releasing moths into cages, then sampling them to determine the number of larvae.
Kerns said a number of factors could negatively affect the data. They range from weather events such as heavy rain and high wind, to the 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. “Really, I just don’t have a good answer for all of the failures. However, based on the data we currently have, the action threshold for bollworms in soybean does not look like it will change much.”