- PRODUCTION -
Most Unwanted Soybean Pests
Redbanded stink bug, the brown marmorated stink bug and the
|By Carroll Smith|
“We had tremendous infestations for several years prior to 2010,” he says. “Then severe winter temperatures in 2009-2010 knocked down the overwintering populations and delayed emergence of the host plants on which they normally feed during the late winter and early spring months. The result was that redbanded numbers were very low at the beginning of the 2010 season, but increased substantially by late fall.”
The seasonal environment during the winter of 2010-2011 was much milder than the previous year, and low levels of redbanded have been scattered across Louisiana in crimson clover and other legumes on levees, CRP and WRP areas. In fact, several stink bug species have been common during the sampling process of those host areas.
“We don’t know what these early detections mean as we move into the soybean production season,” Leonard says. “Stink bugs are primarily pod feeders, and the soybeans have not developed to that level yet.”
Information is being collected to determine the severity of the redbanded stink bug since it is a relatively new pest. Active research projects are ongoing at MSU, Tennessee, Arkansas and the USDA-ARS facility at Stoneville, Miss. As with many stink bug species, the late instar nymphs are at least as damaging, and, in some cases, more damaging than the adults. Chemical control costs have increased, too. Leonard says that in 2007 through 2009 farmers were spraying soybeans for stink bugs about three times more than they had in the 1990s prior to the emergence of the redbanded stink bug as a pest.
“Co-applications of pyrethroids with organophosphates or neonicotinoid insecticides are consistently the most effective and are the primary products used to control redbanded stink bugs in Louisiana and much of the Mid-South,” he says. “Sev-eral of these products are available as pre-mixes, such as Endigo or Leverage 360.
“Also, the action threshold for the redbanded stink bug is lower than that used for other stink bug species. Instead of nine stink bugs per 25 sweeps, we use six redbanded stink bugs per 25 sweeps because this species is more difficult to control and may be more injurious.”
Another important consideration farmers need to be aware of is that just because they don’t see a direct yield loss from these pests, allowing the redbanded to remain in the field above the action threshold can result in significant seed quality losses.
“Soybean seed quality is being affected to the point where some elevators don’t want to take the seed,” Leonard says. “Losses can be such that $13-per-bushel soybeans become $6-per-bushel soybeans.”
‘Kudzu bug’ spreading fast
“In 2010, it had been found in 78 counties in Georgia, 16 in South Carolina, two in Alabama and one in North Carolina,” says University of Georgia Extension entomologist Phillip Roberts. “We also found it in soybeans last year. It is spreading fast.”
Even with one year of data, Roberts believes that it is an economic pest on soybeans.
“Data from two large plot on-farm trials in Morgan and Elbert Counties showed an 11 percent yield reduction in one and a 19 percent yield reduction in the other,” he says. “We also conducted cage trials where we put the bugs in a cage with soybean plants to see how they would impact the plants. We observed fewer pods per plant and fewer seeds per pod. The pest primarily feeds on the main stem, sucking the plant juices.
“Although kudzu bugs don’t feed directly on the pods,” Roberts says, “it does appear that they create an additional stress on the soybean plant.”
The Georgia entomologist says they have been screening many different classes of chemistry, and the bugs are not particularly hard to kill. He believes what happened last year was that two generations occurred, with the first generation appearing on kudzu. When the second generation of immatures became adults, they migrated out of kudzu and into soybeans.
“We anticipate seeing kudzu bugs in soybeans toward the end of June, but we can’t make too many bold predictions based on one year of observation,” Roberts says. “After this year, we’ll have better answers regarding its status as an economic pest and threshold numbers. However, even based on just one year, we will be encouraging farmers to treat for the pest this season.”
Brown marmorated stink bug
“In Maryland in 2009, a few were spotted, but last year they were a severe problem in a lot of their soybean fields,” says Ames Herbert, Virginia Tech Extension entomologist. “When the BMSB hit in Maryland, it was in far larger numbers than our native stink bug species.
“We have one year’s data on cage studies to compare the damage potential of this species to our native species,” he adds. “It appears that the BMSB does more damage bug-to-bug than our native ones do. The BMSB has a longer beak and seems to be a little more hardy.”
Herbert says another problem with this bug is its sheer numbers. Where they may pick up four, five or six native stink bugs in a 15-sweep sample, 30, 40 or 50 BMSBs are picked up. It also appears to particularly affect the edges of fields.
“Right now we have more unknowns that knowns about this pest,” Herbert says. “We’re not sure what it is going to do in soybeans: Keep re-infesting, pass through once or just infest the edges. Our goal is to learn more about the BMSB this year and how to control it. We’re asking everyone to report any sightings.”