The redbanded stink bug took a year off from assaulting Louisiana soybeans in 2010, and the question on grower minds today is whether or not it will return in 2011. According to LSU AgCenter entomologist Jeff Davis, the answer may start to reveal itself as early as April.
Davis spoke at the Louisiana Agricultural Technology and Management Conference in Alexandria La. The conference was sponsored by the Louisiana Agricultural Consultants Association.
No doubt, the redbanded stink bug is the major stink bug pests in Louisiana, according to Davis. Studies conducted in 2009 on soybean plots at the Ben Hur research station indicate that 63 percent to 81 percent of the stink bug species present were redbanded stink bug.
But winter temperatures and spring weather can have a significant impact on in-season populations, according to Davis.
For example, from October 2008 to June 2009, the Red River research station recorded only one hour of temperatures at 20 degrees or below. None of the other stations in the state recorded any hours at 20 degrees or below. The following year was a heavy redbanded stink bug year.
During the same months in 2009-10, however, the St. Joseph station recorded 14 hours at 20 degrees or lower, the Ben Hur location recorded 10 and the Dean Lee station, 5. No hours below 20 degrees were recorded at the New Iberia station in 2010. The following season, only New Iberia reported significant infestations of redbanded stink bug, although they did appear late in the season.
So far this winter, the Red River station has reported 10 hours at 20 degrees and below, the Dean Lee station, 4 and the St. Joseph station, 14.
From this preliminary data, Davis calculates that for each hour at 20 degrees or less, there is an 8 percent decline in redbanded stink bug population. “It will be interesting to see what level of redbanded stink bug populations we have in 2011. Indications are that we may have another low year.”
Drought conditions in April can also impact populations of redbanded stink bugs, according to Davis. “This is when they are emerging from their overwintering sites and looking for secondary hosts to feed on. There are no soybeans podding at that time, so they’re looking for clovers or any other legumes they’ll be able to feed on. In the droughty conditions of April last year, that vegetation did not emerge or they were cut off early and redbanded stink bugs didn’t have a lot to feed on before they moved into soybeans.”
The redbanded stink does have an edge over other stink bugs in that it is simply harder to kill, noted Davis. Adult vial tests indicate that an eight-fold increase in the rate of Karate is required to kill a redbanded stink bug versus a southern green. Nine times as much acephate was required to kill a redbanded stink bug versus a southern green.
“Pyrethroids don’t work as well as they do on southern greens,” David said. “Organophosphates don’t work as well and neonicotinoids don’t work as well either.
Tank mixes are more effective, according to Davis, and include Endigo (which contains thiamethoxam and lambda cyhalothrin), Leverage (which contains imidacloprid and cyfluthrin), and cyfluthrin and acephate.
Davis recommends that growers budget for three stink bug applications per year. “We want you to rotate those products because we don’t want to build resistance to a single product. We need to maintain susceptibility to these products.”
Start with acephate
Davis recommends starting the season with acephate. If you need to make a second application, use either thiamethoxam and a pyrethroid or acephate and a pyrethroid, or a neonicotinoid and a pyrethroid. “If you need to make a third application, we recommend bifenthrin (Brigade, Discipline).”
Davis noted that producers can reduce the volume of material being sprayed on fields infested with stink bugs by going to site-specific applications. “We know stink bugs are aggregated along the borders of fields. If we can reduce the amount of insecticide applied by spraying only those edges, we can save the producers money, protect our natural enemies and hopefully reduce the amount of resistance building up to these various insecticide products.
“If you scout the field, scout more than just the field edges. Scout the entire field. You’ll find that there are some high densities and low densities. Growers will also find that the most damaged soybeans will be along the edges of fields.”
In 1-acre research plots, Louisiana scientists kept stink bugs from achieving threshold in the entire plot by spraying just four rows on either side of 40 rows or more. The field reached three stink bugs per 25 sweeps using this approach.
“We almost zeroed them out by spraying the entire field, but not completely, while our untreated check had almost 14 stink bugs per 25 sweeps. So spraying the edges of the fields worked in small plots. We sprayed only 25 percent of the acreage, so we were saving a lot of pesticide going out and we’re trying to maintain susceptibility to products we have.”
This year, Davis and his team will test the method on larger, grower fields.
Research also indicates that sections of research plots that recorded the highest level of stink bug infestations throughout the year also showed the highest level of green stem, which causes difficulty in combining soybeans. “We also had a lot of damaged soybeans, some secondary infections from fungi — just not very healthy looking soybeans.”
Samples from areas with the least amount of stink bugs, “showed brown stems, brown pods and brown leaves and nice looking soybeans.”
The threshold for southern green, greens and browns are 36 stink bugs per 100 sweeps while the threshold for the redbanded stink bug is 24 per 100 sweeps.
There is some confusion on how to distinguish the redbanded stink bug from the red shouldered stink bug, Davis noted. “The redbanded stink bug is shaped a little more like a football, while the red shouldered stink bug has more of a point to its tips. On the underside, the red shouldered stink bug looks more like a southern green or green stink bug, while the redbanded has a distinctive abdominal point.”