A wake-up call Reduced pyrethroid efficacy against rice stink bugs prompts call for strict adherence to IPM. By Vicky Boyd Editor
Treatment timing is important To help preserve pyrethroids, Lorenz and his University of Arkansas colleagues recommend against tankmixing a pyrethroid with a fungicide for application at the boot spray timing. “That’s two weeks before rice stink bugs will be in the field, so
10
RICE FARMING
|
MAY 2021
BRANTLEE SPAKES RICHTER, UNIVERSITY OF FLORIDA, BUGWOOD.ORG
F
or the past two seasons, University of Arkansas entomologists have documented a concerning decline in the efficacy of a popular insecticide used to control rice stink bugs. The findings about pyrethroids should be a wake-up call for growers to adopt an integrated pest management plan to prolong the products’ efficacy, they said. Included in those practices should be scouting, following treatment thresholds and rotating effective modes of action. “We just don’t have a lot of tools in the tool box,” said Gus Lorenz, University of Arkansas Extension entomologist and director of the Lonoke Research and Extension Center. “If we need to spray for rice stink bug, there’s a limited number of products that are available.” That said, the Environmental Protection Agency is expected to register another insecticide for rice stink bugs in the near future. Even then, growers and consultants will still only have a handful from which to choose. The reduced efficacy of pyrethoids isn’t limited to Arkansas, either. Mississippi State University Extension entomologist Jeff Gore said they’ve received some complaints during the past two years. “In all cases, the consultants have been successful with a second application with a pyrethroid,” he said. “At this point, we haven’t done adequate testing to confirm resistance but plan to do that work.” Kelly Tindall, a field crop research entomologist at the University of Missouri’s Delta Research Center in Portageville, conducted the last tests 10 years ago. At the time, Mississippi rice stink bug populations were more susceptible to pyrethroids than those from other states, Gore said. “So it will be interesting to see how it has changed,” he said. Blake Wilson, Louisiana State University AgCenter rice entomologist, said he also received reports of poor control from lambda-cyhalothrin on a small number of fields in 2019. He also heard from two consultants in 2020 about control issues. “One of the consultants indicated he would spray Tenchu (dinotefuran) on all his acres (in 2021),” Wilson said. “To me, this suggests it’s not widespread, but it was definitely an issue last year and may be getting worse.”
you’re not getting any benefit out of that,” Lorenz said. “And pyrethroids only have a residual of two to three days, maybe five tops.” Growers may view the insecticide addition as cheap insurance, but stink bugs typically don’t move into rice fields until the crop has headed. That’s why the University of Arkansas doesn’t even recommend scouting for the pest until 75% of the heads have emerged from the panicles. Then growers and consultants should continue to scout until grain maturity. By putting out an early pyrethroid application, they are exposing what stink bugs are present mostly along the field edges to the insecticide and selecting for tolerant ones. During the past few years, growers also have had to spray a lot of fields for rice stink bugs later in the season. “I think by the time we got into September, we had knocked out the bulk of the susceptible population,” said Nick Bateman, University of Arkansas Extension entomologist based at the Stuttgart Rice Research and Extension Center. Field trials back up his observations. In 2019, researchers sprayed plots with 1X (label rate) and 4X (four times the label rate) rates of lambda-cyhalothrin. They returned 24 hours later to rate rice stink bug control. Plots that received 4X rates were clean whereas plots that received 1X rate had only about 60% control. The researchers repeated the trials in 2020 and found only about 60% control with both the 1X and 4X rates. RICEFARMING.COM
