August 8, 2007 | By: Laura Skillman
PRINCETON, Ky.

This fall soybean producers in the state may be called upon to help scientists better understand how widespread and damaging the soybean stem borer is in Kentucky and several surrounding states.

The borer is not a new insect. Doug Johnson, entomologist with the University of Kentucky College of Agriculture, has been working for the past several years on what cultural practices may help mitigate its impact. However, to date, planting date, maturity group and variety have shown to be of little help. And until recently, there was no insecticidal control.

The female borer will bite a section out of the node on a soybean plant, put her egg in and then replace the section, sealing the node. This protects the egg from insecticidal sprays. Seed treatments or soil-applied insecticide also have not worked.

Once the larva hatches and reaches a certain size it will tunnel into the stem, ultimately reaching the bottom. With an infestation, the physiological damage from the tunneling can go up to about 10 percent damage, but if the beans fall over, the damage and subsequent lost yields go even higher.

Two years ago a researcher in Kansas got 100 percent control with a seed-applied insecticide that is labeled for use in corn, not soybeans. Further testing on this insecticide is under way at UK, Kansas State and Arkansas, in the hope that it can be labeled for soybeans. This research includes two seed-applied insecticides and two foliar-applied insecticides. 

The university work is an effort to collect data needed to convince the company to pursue the labeling requirements through the U.S. Environmental Protection Agency.

“We probably will be able to collect the efficacy data,” Johnson said. “But getting a pesticide labeled for a particular crop is a very expensive thing to do, so the other data we will need is a distribution of the insect and a calculation of how many acres of soybeans are affected by this insect and to what extent.”

That’s where local soybean growers will play a role. Sometime this fall, as a part of this project, Johnson will contact soybean farmers and ask them if they have the insect, what percentage of their fields might have it and what percentage of plants in the field might have it.

“This is going to be very critical data, because we’ve got to illustrate, providing the product works, that the company can make enough money to go through the expensive labeling process. We will have to come to soybean growers to gather this information,” he said. 

Johnson said it is important that they receive good farmer participation to get the necessary information to present to the insecticide company. But ultimately it will be the company’s decision whether to pursue labeling the product.

“We continue to look at other options to mitigate the risk of damage from the soybean stem borer such as earlier planting dates, early maturing soybean groups and we might see some differences, but they will probably be very small,” he said. “At this time about the only thing a farmer can do is determine whether they have them.”

The easiest way to do this is, when the beans are almost mature, pull up a plant and split the stem. If borers have been active, the stem will be completely hollowed out and sometimes packed with frass. The plants can also snap off easily. It is not uncommon to see the borer, as well. 

To get a picture of how widespread and damaging the insect is, farmers will need to check 20 to 30 plants in a field, then get a percentage of those plants that are infested, a percentage of their fields that are infested and the number of acres in the fields. That’s the kind of information Johnson will collect in coming months to document the need to the company and to the EPA. 

Johnson said they know the insect is in western Kentucky and at least as far east as Lexington, but the eastern edge probably is not very impacted by the insect.

Finding a means of combating the insect will stop the 10 percent loss it inflicts on infested fields, he noted, as well as lessen the likelihood that plants will fall and cause even higher losses.

Contact: 

Doug Johnson, 270-365-7541, ext. 214