The Soybean Spider Mite Problem

Researcher Says Two New Insecticides Could Help

STONEVILLE, MISS.
   New insecticides are showing hope for spider mite control in soybeans, according to Dr. Jeff Gore Assistant Professor of Research at Mississippi State University’s Delta Research and Extension Center.
   “Stinkbugs, three cornered alfalfa-hoppers, and bean leaf beetles are the three most common pests in soybeans,” said Gore, “but spider mites have also become an occasional problem in the last few years. The problem with spider mites is that we have never had effective controls for them in Mississippi until this year.”
   Gore explained two different formulations of bifenthrin have been registered for soybeans this year. FMC has manufactured Hero, a pre-mix of bifenthrin and zeta-cypermethrim also known as Mustang Max, and Brigade, and bifenthrin alone which Gore states are the best option for spider mites.
   “There are timing issues with the applications. With any of the bifenthrin products in soybeans, we have a 30 day restriction meaning that we can only make one application of bifenthrin within a 30 day period,” said Gore.
   So if you make an application of Brigade for spider mites on soybeans you must wait 30 days before you can make another application with any bifenthrin product.
   “Because of that, it’s real important for growers to use the highest labeled rate so that they get the maximum level of control and residual activity,” said Gore, “if farmers use lower rates, they will get some control but the spider mites will just bounce right back because they wouldn’t get much residual activity with the lower rates.”
   Gore has also been focusing on tarnished plant bugs, which is the number one pest in cotton in the Delta area.
   “There are a lot of management options other than insecticides, and some different insecticide use strategies,” said Gore, “one of those strategies is highlighting some of the research that we have done the past few years. We have been looking at shortening spray intervals and found that by shortening the intervals down to four or five days instead of six or seven days, we significantly increase control of plant bugs with the second application.”
   Gore stated that the second application is best because most of the insecticides currently labeled do not provide the same level of control they did in the past. “With a second application, preferably with a different chemistry, the bugs are already weakened,” said Gore, “so by spraying four to five days after the first application, the insects do not have a chance to recover and the second application will work much better. This application should also knock out any young plant bugs hatching from eggs that are present in the field.”
   “It generally takes the eggs about three to five days to hatch during the summer, so a five day interval should kill many of those newly hatched plant bugs,” said Gore. Δ 

Dr. Jeff Gore Assistant Professor of Research at Mississippi State University’s Delta Research and Extension Center, explains the new hope for spider mite control. Photo by John LaRose