V. Todd Miller, Towles, Tyler
Louisiana soybeans are susceptible to damage from a variety of insects, the most economically impactful of which are stink bugs.
The invasive redbanded stink bug, a neotropical insect that ranges from southern South America to the southern United States, arrived in Louisiana about 20 years ago. Historically, it is known to be a significant pest of soybeans in Brazil.
“They’ve easily become the most damaging stink bug in Louisiana soybeans,” said Tyler Towles, LSU AgCenter entomologist at the Tom H. Scott Research and Extension Educational Center in Winnsboro.
Towles and his team are attempting to determine how to more accurately sample and control this pernicious pest.
“Since it’s invasive, we wanted to know how it behaves with our soybean crops,” Towles said. “Does it behave like our native species and, if not, how does that affect the way we scout for it and try to control it?”
Towles said that redbanded stink bugs feed longer and probe the seed deeper. Their salivary enzymes are more damaging than those of our native species. They significantly affect seed quality if they go unchecked, and chemical application doesn’t get implemented in a timely manner.
“We can really take a hit from this pest,” he said.
Towles explained that the typical recommendation was to terminate insecticide applications targeting all stink bug species once soybeans reached the R6.5 growth stage (R6 plus seven days). However, since the redbanded became a recurrent problem, that recommendation has changed to now protect soybeans until at least R7 depending on environmental factors and harvest capability. This recommendation was formed on the basis that the redbanded stink bugs can feed on soybeans that are dried down, reducing seed quality and allowing a route for moisture entry.
The research Towles and his team are conducting has three objectives with a three-year timeline for completion:
Determine the sequence in which the redbanded stink bug shifts between noncrop and crop hosts in Louisiana throughout the spring and summer.
Determine the effect the time of day has on sampling stink bug complex populations using both sweep nets and drop cloths in soybeans.
Compare the usage and efficacy of sweep nets and drop cloths in determining redbanded stink bug population densities in late-stage soybeans.
Being a tropical pest, the redbanded stink bug population is affected by the severity of each winter. This year, Towles said the longer, colder winter pushed his research back, forcing his team to plant soybeans late to maximize the chances of seeing the pest in them.
“A good, cold winter like we had this year can have a detrimental effect on them. This is why we just started planting our trials,” he said. “They have to rebound and make their way back up. After this winter, they got beat back for lack of a better term. We found them in the south-central part of the state, just south of Alexandria and down into St. James and St. Landry parishes. They were low populations, but they were there.”
Towles said it will take some time for the redbanded stink bug to get back up to north Louisiana, but he presumes they will ease their way back up in late August or September, and any soybeans that were planted late will likely be affected.
In other pest-management research, Towles and his team evaluated several neonicotinoid and fungicide soybean seed treatments in northeast Louisiana to determine the value of this technology in seed and seedling stage soybeans. Last year, they did not see a significant difference among seeds treated with neonicotinoid, fungicide or neonicotinoid plus fungicide seed treatments compared to untreated seed. He chalked this up to low populations of soil-dwelling pests and ideal environmental factors at planting in the spring.
Several insecticides were also tested for efficacy and residual against greater-than-threshold-level populations of brown, green, southern green and redbanded stink bugs in soybean plots. Treatments included pyrethroids, organophosphates and neonicotinoids applied as stand-alone products in addition to pyrethroids plus organophosphates and pyrethroids plus neonicotinoids. Data from 2020 field trials illustrated that a pyrethroid coupled with an organophosphate (bifenthrin plus acephate) or a pyrethroid coupled with a neonicotinoid performed extremely well in reducing stink bug populations from two-times-threshold back to subthreshold levels.
Another highly preforming product mixture was Leverage 360 coupled with acephate (neonicotinoid plus pyrethroid plus organophosphate). These treatments significantly reduced stink bug populations compared to the untreated check. The data showed that coupling either a pyrethroid with an organophosphate or a neonicotinoid and a pyrethroid for the control of the native stink bug complex plus the redbanded stink bug are the superior options.
They also attempted to evaluate the efficacy of many insecticides for the control of soybean loopers and corn earworm in soybeans. However, because of the combination of low corn earworm pressure, epizootic control of soybean loopers and hurricanes in northeast Louisiana, this trial was not successfully completed and will be executed again this year.
The redbanded stink bug feeds longer, probe the seed deeper and their salivary enzymes are more damaging than those of our native species. They significantly affect seed quality if they go unchecked and chemical application doesn’t get implemented in a timely manner. LSU AgCenter photo
One of Tyler Towles research team’s three objectives in studying the redbanded stink bug involves comparing the usage and efficacy of sweep nets and drop cloths in determining redbanded stink bug population densities in late-stage soybeans. LSU AgCenter photo