16 minute read
rice system
A wake-up call
Reduced pyrethroid efficacy against rice stink bugs prompts call for strict adherence to IPM.
By Vicky Boyd
Editor
For 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.”
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 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.
Scout, follow thresholds
As part of an IPM program, the entomologists say growers and consultants should scout and only make applications when thresholds are met or exceeded. Check with state Extension entomologists for rice stink bug thresholds in your state.
During the fi rst two weeks of heading, the University of Arkansas recommends treating if stink bug densities average fi ve or more per 10 sweeps. During the third and four weeks of heading, applications are recommended when stink bug numbers reach 10 insects per 10 sweeps.
Based on research, the University of Arkansas has found insecticide applications are warranted until 60% hard dough is observed across 50% of the fi eld.
Because kernels can be at different stages of maturity on the same panicle, a simpler method involves counting the number of straw-colored grains and green-colored grains. If 60% or more of the grains are straw colored across 50% of the fi eld, then growers won’t see a benefi t from an insecticide application.
Rice stink bug infestations also tend to be worse in early and late-planted fi elds because the insects key in on the few fi elds in the area with headed rice on which to feed, Bateman said. In the middle of the season, stink bugs are more dispersed among the numerous fi elds in the area with rice at heading.
Growers can still use pyrethroids for the fi rst application, but the entomologists recommend rotating to a different mode of action should stink bug populations rebound and exceed thresholds once again.
In the majority of University of Arkansas fi eld trials over the years, stink bug control did not differ signifi cantly between Tenchu 20SG and lambda-cy, Bateman said.
“When you get to those bad numbers, if you have to make a second application after lambda, you’re probably going to have to make a second application after Tenchu, too,” Lorenz said.
But Lorenz said he understands the economics behind growers’ decisions to lean heavily on lambda-cy.
“It’s really hard to get away from lambda when it’s a buck and a half (per acre),” he said. “But if we have an issue with stink bug resistance to lambda eventually, it’s going to mean a lot more money for the growers to control them. Especially if we have to treat a couple of times, you’re looking at the cost of the product plus the cost of the airplane or $50 to $60 per acre, and you don’t want to do that.”
Belchim Crop Protection, which markets Tenchu 20SG, has listened and plans to reduce the price of its insecticide by more than 20% this season, said Don Long, Belchim national technical service and development manager.
In addition to providing residual control of up to two to three weeks, he said dinotefuron, the active ingredient in Tenchu, is safe to use around crawfi sh.
New registration pending
Federal and state registrations are pending on another stink bug material, Endigo ZCX, from Syngenta. The premix contains lambda-cyhalothrin and thiamethoxam. During the past few years, University of Arkansas Extension entomologists had the product in fi eld trials where the “results were very positive,” Lorenz said.
“The performance of Endigo was better than lambda overall, but I don’t know how much residual you get from the thiamethoxam part of it.”
Whether growers use the product once it is registered will likely depend on the price, he said.
Recently, Lorenz said they received a phone call asking about the effi cacy of carbaryl for rice stink bugs. Although the insecticide has performed well in trials, he said many other countries will reject commodities that test positive for carbaryl residue. As a result, he would not recommend the product for rice stink bug control.
Aaron Cato, then a senior entomology graduate student, demonstrated improved field sweeping techniques in 2018. Cato is now a University of Arkansas Extension specialist, horticulture IPM. Wait until 75% heading to begin scouting for rice stink bugs, and only treat when thresholds are met.
Got billbugs?
Combination seed treatments help reduce damage and increase yields, but you must plan ahead.
As the number of row rice acres increases, so does the potential for infestations and damage by billbugs — inch-long weevils that prefer dry land over fl ooded ground.
In 2020, Arkansas growers planted about 230,000 acres — or about 16% of the overall state acreage — of row rice, also known as furrow-irrigated rice. And some industry experts expect the trend to continue with a modest increase this season.
Through trials and observations in both the fi eld and greenhouses, University of Arkansas researchers continue to unravel the mysteries behind the rice billbug. Although many questions remain and a number of new ones have cropped up, they have found that overtreating seed with a diamide insecticide helps reduce the pest and associated damage.
Still to be addressed are the number of generations, reproductive rates, alternate hosts, potential foliar treatments, possible treatment thresholds, and pheromone or plant-based attractants for trap lures.
Entomologists at Mississippi State University and the Louisiana State University AgCenter also are conducting billbug trials based on their geographic production practices.
A one-two combo
For the past two years, graduate student Chase Floyd has been working with University of Arkansas Extension entomologists Gus Lorenz, Nick Bateman and Ben Thrash as part of his doctoral research into billbugs. They plan to continue their research this season.
Although trials show combination seed treatments signifi cantly improve yields in billbug-infested fi elds, the researchers say growers and consultants need to think proactively.
By Vicky Boyd
Editor
Under a worse-case scenario, billbugs can cause significant yield loss.
Adult billbugs may overwinter buried 5 to 6 inches deep in soil.
In Arkansas, rice growers tend to favor a neonicotinoid seed treatment, such as NipSit Inside or Cruiser Maxx, because it controls both rice water weevils and grape colaspis. Although diamides also are strong on rice water weevils, they do not have activity against grape colaspis, a soilborne pest that also feeds on soybeans.
University of Arkansas researchers have had encouraging fi eld trial results when they applied Fortenza or Dermacor seed treatment over seed already treated with a neonicotinoid. Fortenza and Dermacor are diamides.
Hybrids from RiceTec typically come with the Cruiser Maxx Rice seed treatment, which contains thiamethoxam. Adding a Fortenza overtreatment adds about $7 to $8 per acre whereas adding Dermacor will run about $12 per acre, Bateman said.
In trials, a diamide overtreatment resulted in an average yield increase of 15 bushels per acre, more than paying for itself, he said. The results were similar whether or not billbugs were present.
“We can make it pay for itself, regardless of pest pressure,” Bateman said. “If billbugs were present, the diamides will help reduce their numbers but it won’t be 100%.”
That’s because even as they fed on plants treated with Fortenza or Dermacor, it took six and nine days, respectively, for the weevils to die, Floyd said, referring to greenhouse trial data. In those same trials, it took 19 and 21 days for billbugs to die as they fed on plants treated with NipSit and Cruiser Maxx, respectively.
Foliar treatments struck out
The University of Arkansas researchers also looked at foliar applications of several insecticides, both registered and unregistered. They hoped to fi nd products growers could use once they saw damage. Unfortunately, the researchers have so far struck out.
“As far as treatments from a foliar standpoint, we haven’t found anything that’s reliable,” Bateman said. “We see no reduction in damage from a foliar standpoint.”
That may be due to the billbug’s behavior of feeding at the base of young rice plants. The female chews a small hole at the base of a plant into which she deposits a single egg.
The larva is protected as it feeds inside the tiller as well as below the soil surface into the crown. It is this feeding by both adults and larvae that causes leaves to die and panicles to blank.
A dead leaf, surrounded by green vegetation, is a red flag that billbugs were likely feeding on that plant.
Survey for symptoms
Walking through fi elds, Floyd said he found feeding holes 91% of the time he examined dead leaves. Seeing that got him thinking about how it could be used to determine billbug presence rather than waiting until you see blank panicles later in the season.
“The fi rst sign they’re in the rice is if you’re looking at the tillers as that new plant material is coming out of the growing point, it will be completely dead,” Floyd said. “It will stick out like a fl ag. The biggest thing to get used to is the sheath will still be green, but new material coming out of the sheath will be yellow.”
Based on surveys conducted in 2019 and 2020, Floyd said he saw the fi rst billbug feeding symptom — a dead leaf — 58% of the time at the three- to four-tiller growth stage. And 83% of the time he saw the fi rst symptom before green ring.
The leaf dies fi ve to six days after adult billbug feeding, Floyd said, citing limited greenhouse studies. But he was quick to point out that the studies were under controlled conditions and may not represent what is happening in the fi eld.
Interestingly, plants with dead leaves
2021
Recognize an outstanding consultant for his or her dedication, leadership and innovation in the U.S. rice industry.
For more information, go to ricefarming.com/rcoy or go toPage 15in this issue of Rice Farming.
Submit nominations by July15, 2021.
SPONSORED BY
Abbreviated Rules. No Purchase Necessary. Contest ends on 7/15/21 at 11:59:59 PM (CT). To enter, go to http://www.ricefarming. com/rcoy. Nominators must be legal residents of the fifty (50) United States and District of Columbia who are 18 years of age or older at the time of entry and possess knowledge and/or experience in the rice farming industry. Entrants must be legal residents of the fifty (50) United States and District of Columbia who are 18 years of age or older at the time of entry and serve as a rice consultant in the rice farming industry.Void where prohibited. Sponsor: Corteva Agriscience, 9330 Zionsville Road, Indianapolis,IN 46268. Billbugs are inch-long weevils that prefer dry ground to flooded rice paddies. As a result, they have become an increasing problem in row rice, also known as furrow-irrigated rice.
respond by producing two more tillers than the non-infested plants, he said.
“It seems the rice is trying to compensate, but it’s not enough,” Floyd said. In the end, infested fi elds typically yield less than uninfested fi elds, with the reduction depending on the extent of the infestation.
This year, he said he hopes to develop a sliding scale to assess the infestation severity based on the number of dead leaves and healthy tillers per plant.
Where billbugs spend the winter
The researchers have yet to pinpoint where most billbugs overwinter, although Floyd has found them along the edges of previously infested rice fi elds in the soil buried 5 to 6 inches deep. He also has surveyed grassy turn-rows around harvested rice fi elds and found larvae and pupae as well as adults.
The researchers believe adult billbugs may spend the spring in these grassy edges and move into row rice fi elds as plants reach the three- to fi ve-tiller stage. But they’ve also noted a signifi cantly greater risk of infestation should a row rice fi eld have a previous history of billbugs and be near a tree line.
In addition, fi elds farmed continuously in row rice, such as one in Jackson County that has been in the system for fi ve years, appear to allow pest numbers to build.
“The billbugs haven’t had to seek out other hosts, and the damage has consistently gone up on a yearly basis,” Bateman said.
Crop rotation also doesn’t appear to affect populations. Floyd said he had visited a severely infested row rice fi eld near
In 91% of the cases where dead leaves were observed, Chase Floyd found feeding holes.
Stuttgart in 2019, and he found the pest overwintering in nearby grasses. In 2020, the farmer rotated to soybeans, and the billbugs just seemed to move to an adjacent row rice fi eld.
“Gus, Nick and Ben all went to that fi eld in 2020,” Floyd said. “It was the worst fi eld I saw across the state.”
The researchers also suspect that billbugs migrate into row rice fi elds and are possibly drawn by plant volatiles emitted when the plants begin to tiller.
As a result, Neelendra Joshi, an associate professor in the University of Arkansas Department of Entomology and Pathology, is working to identify possible pheromones or plant volatiles that could be used as trap lures.
NOMINATION FORM
Nominate an outstanding consultant for the Rice Consultant of the Year Award. Sponsored by Corteva Agriscience and Rice Farming magazine, the annual award recognizes the dedication, leadership and innovation of this crucial segment of the U.S. rice industry. “Crop consultants are invaluable to rice farming operations throughout the Mid-South. The agronomic advice consultants provide ensures the future profitability and viability of the rice industry for generations to come,” says Clark Smith, product manager for rice herbicides, Corteva Agriscience. “At Corteva, we are honored to sponsor the Rice Consultant of the Year Award, recognizing those consultants who most exceed expectations for their contributions to the rice industry,” he says. The RCOY Award recipient will: Be featured in a four-page salute in Rice Farming magazine and honored at a special recognition event. Receive a personalized Rice Consultant of the Year jacket. The award recipient and nominator each will receive one night’s hotel stay and round-trip travel to the event.
SUBMIT SUPPORTING DOCUMENTATION
Please use a separate page for biographical/professional information.
Additional recommendation letters from rice farmers, consultants andindustry members in support of the nominee are encouraged.
Submit all materials via:
Email: csmith@onegrower.com Mail: Carroll Smith 7201 Eastern Ave. Germantown, TN 38138 Online: ricefarming.com/rcoy
Submit nominations by July 15, 2021.
Consultant’s Name: Company Name: Mailing Address: City: Phone: State: Email: ZIP:
Please describe the dedication, leadership and innovation that makes this person
a good candidate for the 2021 Rice Consultant of the Year Award. (Be as specific as posible, and use a separate sheet, if needed.)
Your Name: Address: City: Phone: State: Email: ZIP:
SPONSORED BY
