EPA has granted a Section 18 Emergency Exemption for Transform WG insecticide to North Carolina for control of tarnished plant bugs (TPB) in cotton.
While TPB has historically been most problematic in the Midsouth, populations are increasing in North Carolina.
“Until 2010, no more than 5% of cotton acres in North Carolina were sprayed for plant bugs,” says Dominic Reisig, associate professor and Extension entomology specialist at North Carolina State University (NCSU). “Since then, more and more acres are being sprayed every year. Last year, 75% of North Carolina’s cotton acres received at least one spray. Increases in plant bug populations are significant enough, along with economic thresholds, to justify an insecticide application.”
In addition to the increasing incidence of plant bug infestations, this piercing, sucking pest is also expanding its geography.
“Prior to 2016, the plant bug problem was mostly confined to the northeast part of the state and was mostly associated with vegetable production,” Reisig says. “That was the epicenter. It has since expanded geographically. While 2017 was a lighter infestation year, more fields were sprayed because plant bugs had expanded into areas where they weren’t before.”
Field trials validate efficacy
In 2016 and 2017, Reisig conducted research comparing several plant bug insecticide treatment options to untreated checks. The studies involved replicated field trials with both early and late plantings. Results were consistent over both years, showing net returns higher using established thresholds versus an untreated check.
“The 2017 efficacy study is one of the things that helped us go forward with the application recommendation, because control with Transform was very effective,” Reisig says. “Results remained consistent with 2016 data when 2017 threshold trials included Transform exclusively. In each case, the insecticide recorded higher net returns over the untreated control. Transform is certainly an insecticide that the NCSU Extension recommends for effective control of tarnished plant bug. It pays to spray.”
Establishing economic treatment thresholds
NCSU has established two different economic thresholds for North Carolina cotton based on plant development. For pre-bloom, NCSU recommends a tandem scouting approach. A threshold of eight tarnished plant bugs per 100 sweeps is combined with square retention monitoring.
“We want cotton growers to observe the nodes on top of the plant,” Reisig says. “If they’re missing more than 20 percent of those, anything below 80% square retention would trigger a spray.”
The post-bloom threshold is based strictly on numbers. Historically, there is a higher occurrence of nymphs present post-bloom. At that point in the season, Reisig says growers should use a drop cloth to determine treatment thresholds, because a sweep net is not as effective capturing nymphs. The NCSU Extension post-bloom threshold recommendation is two to three plant bugs per drop cloth sample.
Transform’s active ingredient, Isoclast (sulfoxaflor), is the only member of the Group 4C class of insecticides. Transform delivers both contact and residual and does not flare spider mites or aphids, and has minimal impact on beneficial insects.
“For us in North Carolina, Transform will be a great product, not only for control, but also to help address an emerging resistance to pyrethroids and organophosphates,” Reisig says. “Transform is a great rotational partner that growers didn’t have before receiving the Section 18.”
What’s ahead for 2018?
Reisig says early season wet weather conditions were ideal for growing weeds that serve as primary plant bug hosts. Although it is a bit too early to predict, all signs point to early and possibly heavy plant bug infestations across the state.
“So far, it looks to be early and heavy,” Reisig says. “We had a lot of rain early on, which is good for weeds and early season hosts. All these things really help out plant bug populations a lot.”