Bucket traps aid University of Arkansas research into new row-rice pest, control measures.
• By Vicky Boyd,
University of Arkansas entomologists continue their quest to learn more about the rice levee billbug, a weevil pest that until recently only caused occasional issues for levee rice. With the increasing popularity of row rice — also called furrow-irrigated rice — the billbug has risen in importance as a rice pest, especially in the upper third of fields that aren’t under a permanent flood.
During 2019, Arkansas growers planted more than 100,000 acres of row rice, and that number is expected to grow in coming years. As the new system expands, so, too, will new agronomic issues.
“It’s not just insects,” says Dr. Nick Bateman, University of Arkansas Extension rice entomologist. “It’s weeds and fertility and disease issues. It’s a totally new system. Billbug is the first big one that has jumped up. There may be more pests insect-wise that will manifest themselves as time goes on and the acreage increases.”
Robb Dedman, a crop consultant who works in Southeast Arkansas, says he hasn’t seen significant damage yet in the row-rice fields he scouts. But he’s keeping a careful watch.
“It’s in the neighborhood,” Dedman says. “Right now, I think the majority of billbugs are on the (Grand) Prairie. But I think as we continue to move to more row rice or row rice-bean rotations, we’re going to see the numbers elevate. I think it’s a situation that will continue to get worse if we don’t manage it.”
Comparing billbugs to any other pest, he says an integrated approach will be needed to gain the upper hand.
Billbugs, the dry ground relative
Rice levee billbugs belong to the beetle family, Curculionidae, as do rice water weevils. But unlike rice water weevils, which favor flooded rice fields, billbugs seek dry ground.
In many row-rice fields, growers board up the bottom to catch and back up irrigation water flowing from the top. It is the top third, which is furrow irrigated much like soybeans and has periods of dry soil, that billbugs typically infest.
After hatching, billbug larvae burrow into rice stems, where they feed and deprive the developing grain head of nutrients. The result can be blanked heads, which by the time they’re visible are too late to treat.
By spending much of their life in tillers, larvae also are protected from foliar-applied insecticides.
Until recently, billbugs were an occasional pest of rice levees that typically received little attention. As such, little research has been done on their biology and possible alternate hosts.
But Bateman says studies underway are designed to fill in some of the knowledge gaps.
A bucketful of data
Using 5-gallon hot pink plastic buckets, Chase Floyd — a University of Arkansas entomology student working on his doctorate degree — trapped row rice fields from northern Louisiana to the Missouri Bootheel during the 2019 season. Anecdotal information points to billbugs being attracted to the hot pink color more than to white or to yellow.
Floyd placed the buckets on edges of rice fields and weighted them down with a bit of dirt. He returned weekly to count the number of weevils that crawled under the buckets.
“What he found is 55% to 60% of the fields where he had buckets had billbugs, so it looks like 60% of the row rice had some level of billbugs,” Bateman says. “In some of those cases, he was catching one out of the whole field. In some cases, he was catching multiple billbugs per week.”
Although the buckets served as a monitoring tool to detect the presence of the pest, Bateman says they haven’t yet been able to correlate number of billbugs to damage severity.
He says they also evaluated yellow sticky traps as well as a modified malaise trap, where the weevils would be attracted to a light and fly into funnel-shaped netting.
“We tried every trap we could find, and those buckets seemed to work the best out of any of them,” Bateman says.
Part of their goal is to determine exactly when billbugs enter rice fields. Visual damage, such as tillers dying, seems to begin around green ring, prompting Bateman to theorize the billbugs are entering a field one to 10 days before green ring.
“It’s probably the fourth or fifth tiller when they’re really targeting that field,” he says. “There’s very little information out there, so we’re trying to figure out a whole lot of things.”
Does the movement of billbugs correlate to the rice plant growth stage or does it have more to do with degree days? Those are questions Bateman says remain unanswered.
Developing a pheromone attractant
As part of that effort, University of Arkansas chemical entomologists in Fayetteville as well as those with the U.S. Department of Agriculture Agricultural Research Service in Stoneville, Mississippi, are working to identify a pheromone to use as a trapping lure. Bateman and fellow entomologist, Dr. Gus Lorenz, say they remain hopeful since billbugs belong to the same family as boll weevils.
“We know how much the pheromone played in controlling and ultimately eradicating the boll weevil,” Lorenz says. “We were able to achieve that with the boll weevil because of the development of the pheromone. We feel like that might help us to understand (billbug) activity and understand when it’s coming into a field and to see how big the population is.”
Knowing when billbugs begin entering a field also could help with timing a foliar insecticide spray. Ongoing trials are looking at different foliar insecticides.
Over-treating standard seed treatments
Preliminary research led by Bateman has found over-treating a standard neonicotinoid seed treatment with a diamide insecticide — either Dermacor or Fortenza — appears to control both rice water weevils and billbugs. The neonicotinoid is needed to pick up grape colaspis, a soil-borne pest common in rice fields rotated with soybeans. The diamides offer longer residual weevil control than neonicotinoids but have little effect on grape colaspis.
Even in the absence of billbugs, the overtreatment appears to boost yields by up to 38 bushels per acre, he says. More commonly, yield increases ranged from 10 to 25 bushels per acre.
“In a lot of the cases, those guys who get grape colaspis get rice water weevil,” Bateman says. “What we saw in those situations — particularly in those situations where they had grape colaspis, then had rice water weevil come in behind — the combination treatments excelled.”
Rice water weevils tend to overwinter in plant litter, especially along tree lines. Whether billbugs do the same remains unknown.
Following the 2019 season, the researchers surveyed around fields that had heavy billbug infestations. What they observed was as temperatures began to drop, the insects moved farther down into the root mass.
They also found some on the edges of fields in bermudagrass, suggesting billbugs may begin to migrate from fields in early September at harvest to nearby host plants.