LSU AgCenter entomologists are concerned that a relatively new insect may play havoc with the state’s soybeans, but they’re hopeful the destructiveness may not be severe.
Red-shouldered stink bugs may be a growing problem, but experts still haven’t figured out the extent of the damage they will cause in 2005. “It’s too early to say for sure,” said LSU AgCenter entomologist Jack Baldwin.
AgCenter researchers first noticed this stink bug in light numbers in South Louisiana at the AgCenter’s St. Gabriel Research station in 2000. In 2002 and 2003, populations of the pest became high enough for testing insecticides on it, Baldwin said.
In 2004, red-shouldered stink bugs were prevalent in the “cane belt, the area of South Louisiana where farmers grow both soybeans and sugarcane,” Baldwin said. They spread west and north and were eventually found in Southwest and Northeast Louisiana by the end of the year.
“This year, we know they’re present,” Baldwin said. “They were found in February and March in clovers and vetches, and by May they were in soybeans.
“We don’t know about a month from now,” Baldwin said in late May. “Their presence suggests they could be a problem again.”
The insects are smaller than the southern green stink bug and brown stink bugs, which have been in Louisiana soybean fields for years. They feed on pods and reduce yield and seed quality, Baldwin said.
Red-shouldered stink bugs are responsible for delayed maturity in South America, where they’ve been a problem for some time. But in Louisiana, “they haven’t been a problem that we know of until the last couple of years,” Baldwin said.
A significant problem with the red-shouldered stink bug is that it’s tougher to kill than green stinkbugs and several species of brown stink bugs. After treating a field for stink bugs with an insecticide, Baldwin said, “Red-shouldered stink bugs are about all that’s left.”
If a grower finds red-shouldered stink bugs in a soybean field, Baldwin suggested lowering the threshold used for treatment. AgCenter entomologists have lowered the recommended economic threshold for stink bugs from 36 bugs per 100 sweeps to 24 per 100 sweeps.
“Red-shouldered stink bugs are the ones you don’t want to develop or build up in a soybean field,” Baldwin said. “It’s a judgment call, but I would not let a threshold get to 36 if there is a high percentage of red-shouldered stink bugs in a field.”
The adult of this bug is light green colored and a little more than a half inch long – about three-fourth the size of an adult southern green stink bug, the entomologist said. They have a reddish-orange band across the back, right behind the head.
Baldwin said red-shouldered stink bugs apparently move from field to field as soybeans approach the bloom stage. And they’re visually different from the southern green or brown stink bugs. “It’s pretty apparent,” he said.
Because the insect is relatively new in Louisiana, entomologists are basing their approach to control on their experience with other stink bugs. Researchers have determined Orthene is the recommended insecticide, which has two 24-C special labels in Louisiana.
Baldwin said researchers still don’t know much about this relatively new pest. “We don’t know if they’ll be ‘annual’ or periodic,” he said. “Time will tell how it fits into soybean production in Louisiana.”
Given the difficulty in controlling them, entomologists are hoping the pest won’t be a perennial problem.