For the past several years, stink bug numbers have been fairly low in Louisiana soybeans, but this year they are much higher. The main culprit, the redbanded stink bug, if left unchecked, can cause damage so extensive that farmers may lose an entire field of beans.
“This is very costly to growers when soybeans are selling at nearly $16 per bushel, with the state production average at 35 bushels per acre,” saidLSU AgCenter entomologist Jeff Davis.
That could mean a loss of nearly $60,000 for a farmer who loses a 100-acre field to this pest.
For nearly three years, Davis has been studying ways to control stink bugs. His research has shown that there’s more than one way to gain control of the damaging redbanded stink bug in soybeans. That’s the thinking behind multiple management strategies in Louisiana fields. Davis has been looking at four main ways to control stink bugs in trials across the state -- insecticides, host-plant resistance, biological controls, and timing of insecticide applications.
“Typically, the first tactic is go out and count the number of insects. Once that number reaches the action threshold, growers will make an insecticide application.”
Scouting for insects involves using a sweep net and then counting how many insects are captured in the net. The action threshold is the point where insect populations are high enough to warrant the cost of an insecticide application to prevent significant crop losses.
“Insecticides are our first line of defense, but we have to put out so much here in Louisiana. The LSU AgCenter recommends three to five applications per year for insect control in soybean. And this year we’ll probably use them all.”
Another strategy used in the control of the redbanded stink bug is host-plant resistance. Here Davis looks for varieties that have natural resistance for stink bugs.
“What this means is in these fields, stink bug populations are kept low. And even when they are present, damage is minimal because they just don’t feed on these plants as much.”
This strategy also helps to keep insecticide applications low. “For instance, we may need to make two to three applications in susceptible varieties, but only need one to two in resistant fields,” Davis said.
Biological control is also useful in managing the stink bug populations. “Here is where we use natural enemies like fire ants to control pest insects. There are also native parasitoid wasps that do a good job, but they are highly susceptible to our pyrethrin insecticides.”
This year the redbanded stink bug came earlier than usual. Davis started getting questions from farmers in early May. “I usually don’t get questions before late June or July.”
A problem facing Davis is how to implement management strategies without killing beneficial insects. “When plants are damaged, they signal to beneficial insects that their help is needed. However, the insecticides we use to kill insect pests also kill the beneficial insects.”
The goal of the insect management program is to reduce the number of insecticide applications, reduce the effect on the environment, and keep the grower’s cost down.