Destructive Stink Bugs Show Up In Soybeans Earlier Than Expected

BATON ROUGE, LA.
   Jeff Davis, LSU AgCenter entomologist, is finding stink bugs in agricultural fields earlier this year than expected.
   “We found them active in clover all winter. We even found them reproducing in the winter, and they are not supposed to be,” he said.
   More alarming, though, is his finding of redbanded stink bug nymphs on June 3 on soybeans only 8 inches tall, and adult redbanded stink bugs in 12-inch-high soybean plots. Both discoveries were at the South Farm of the Rice Research Station in Crowley, where he rarely finds any stink bugs.
   If left unchecked, the redbanded stink bug can cause damage so extensive that farmers may lose an entire field of beans, Davis said. The redbanded stink bug is the No. 1 pest of Louisiana soybeans.
   “We are not supposed to be finding stink bugs in Louisiana this early in the vegetative stage. All the literature says we won’t find them until pods have developed,” Davis said.
   He is working this year with a new sampling device that uses a leaf blower on a backpack to suck insects from soybean plants. He said the vacuum finds insects often missed with sweep nets, which can also damage small plants.
   Davis has two studies funded by the Louisiana Soybean and Grain Research and Promotion Board. The first study will examine possible traits that make some varieties of soybeans undesirable to soybean pests, while integrating natural enemies of the pest and insecticides.
   The second study is aimed at determining when stink bugs move into a soybean field and how they survive winters.
   Clover appears to be a bridge species that harbors stink bugs until soybeans are growing. Farmers who use clover as a cover crop should be aware that killing the clover could cause stink bugs to move into a soybean field, he said.
   Two other insect pests are also problematic for Louisiana soybean growers, Davis said. The kudzu bug was found near Vicksburg, Miss., and the brown marmorated stinkbug has been found in Texas.
   To detect possible movements of those two insects into Louisiana, small plots of 10 highyielding soybean varieties were planted at several research stations, and they are sampled weekly.
   “We use them as our early warning system,” Davis said.
   Yield and quality will be examined after harvest, he said. Half of the research plots will be sprayed, and half will be left unsprayed for comparison.
   The brown marmorated stink bug is not in Louisiana yet, he said, but discovery of the kudzu bug just across the Mississippi River from Louisiana means the pest could be found in soybeans soon.
   Alabama and Georgia soybean farmers have found the kudzu bug in their crops. Yield losses in untreated fields could be as high as 40 percent, Davis said, but several insecticides are available that are effective against the insect.
   Davis also will be monitoring insect pests for insecticide resistance. He said some populations of stink bugs were showing resistance last year. Δ

A redbanded stink bug found on June 3 in a soybean field at the South Farm of the Rice Research Station near Crowley. The discovery surprised Jeff Davis, LSU AgCenter entomologist, who said the pest normally isn’t found in soybeans until the plants have developed pods. Photo by Bruce Schultz

Jeff Davis, LSU AgCenter entomologist, uses a vacuum-like device to check research plots for stink bugs at the South Farm of the Rice Research Station. Photo by Bruce Schultz