Combination seed treatments may kill two weevils with one blow.
• By Vicky Boyd,
Editor •
A weevil that prefers drier ground and typically frequents rice levees has begun damaging furrow-irrigated rice, thanks in part to a lack of permanent flood in the upper portions of the fields. At the same time, producers of row rice — as the system is also called — may also have to deal with water-loving rice water weevils in the lower portions of their fields that they’ve boarded up to catch irrigation runoff.
Preliminary research led by University of Arkansas Extension rice entomologist Nick Bateman has found over-treating a standard neonicotinoid seed treatment with either Dermacor or Fortenza appears to control both weevil pests.
Bateman stresses the results are from only one site and from only one season, but he says they look promising.
A bug of mystery
One of the challenges is very little is known about rice levee billbug’s biology, reproduction and overwintering habits. Entomologists could find billbugs during hot, dry years, but they were typically relegated to the levees and growers seldom worried about them. That was until row rice acres began to increase.
“Row rice is going to open up a whole new can of worms in terms of insect issues,” Bateman says. “You eliminate a lot of dispersion of rice water weevil, which is our No. 1 insect pest. And it also increases grape colaspis damage.”
As part of his research this season, Bateman plans to enlist several county agents to put out different traps, ranging from pink and yellow sticky panels to blacklight and bucket traps. He hopes the trap catches will help shed light on some of the billbug unknowns.
Wendell Minson, a consultant near Dexter, Missouri, has talked to Bateman about also putting out traps in the Bootheel. In the area he serves, row rice acres have taken off.
During the past couple of years, he and a colleague who also serves the Bootheel, Tim Flowers, have seen an increase in billbug pressure.
“Last year we started to see it a little more, and we both saw it at the same time,” Minson says. “We started to try to figure out what it was — we put 2 and 2 together.”
Flowers says they have seen billbugs on levees or around the edges of fields in the past, so the insect isn’t new. “But it’s a new problem that we’re not used to dealing with, and it’s beginning to cause concern,” he says.
Minson says he suspects billbugs will become an increasing problem as more growers adopt row rice. At the same time, some of his growers have gone to much lower beds that resemble a graded field with little grooves.
The practice appears to improve wicking, allowing better water movement and keeping the area moist longer. And Minson wonders whether the wetter soil will be less hospitable to billbugs.
“We know that billbugs don’t like that wet culture, so that might be helping us a little bit,” he says.
More trials in the works
In 2018, Bateman conducted trials on a farm in Jackson County, Arkansas, that examined different seed treatments for billbug control. This year, he plans to expand the trials to three or four locations, including near Stuttgart and in Southeast Arkansas.
Bateman also will lead trials looking at foliar insecticides to possibly control billbugs in-season, but application timing may be tricky. 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.
“That’s why I don’t have a whole lot of faith right now in our Karates and Belays — they don’t have very long residuals,” he says.
In the turf industry where they battle a related billbug, traps are used to determine when the pest has moved into an area.
Then a DD50 model predicts the optimum spray timing. The program has been used successfully for Kentucky and Tennessee golf courses, Bateman says.
Whether a similar model would work for levee billbugs is uncertain. At the end of last season, he found billbug life stages ranging from newly hatched larvae to adults, leading him to think there may be a continuous migration of billbugs into fields.
A tale of three environments
Many row rice fields actually provide three different environments within one block.
The upper one third is dry except when irrigation water runs down the furrows. This is where billbugs concentrate because of a lack of permanent flood.
The middle one third is similar to AWD, or alternate wetting and drying, where there are prolonged periods of moist soil.
The bottom third resembles a conventional rice field with a permanent flood, since many growers install boards at the bottom that capture and back up run-off from the top portion. Rice water weevils also tend to concentrate in this section because of the flood.
During 2018, Bateman conducted minor billbug surveys of fields as he drove around to visit producers.
“It wasn’t hard to find billbug damage in almost all of the row rice fields, but there were low numbers that wouldn’t be yield limiting,” he says. “In a few areas around Newport, there were a couple of hot spots, but the fields have also been in row rice for three to five years now. So it’s looking like right now, you see a little bit of damage, it builds up and then all of a sudden, they have major issues.”
Overtreatments performed well
Because row rice fields may host both billbugs and rice water weevils, Bateman wanted to determine whether seed treatments could be used to control both pests. During 2018, he looked at a number of products, both individually and in combination.
Arkansas rice producers have traditionally used either CruiserMaxx or NipsIt Inside because they control rice water weevil as well as grape colapsis, a pest that is particularly troublesome in rice fields rotated with soybeans. Efficacy of either neonicotinoid seed treatment begins to fade 28-35 days after the seed is put in the ground.
Dermacor X-100, another seed treatment, isn’t used as much in Arkansas as it is in South Louisiana. Although strong on rice water weevils, stem borers and armyworms, it is weak on grape colapsis, which aren’t a big problem in South Louisiana.
From Corteva Agriscience, Dermacor contains the active ingredient, chlorantraniliprole.
Bateman also included the Arkansas standard treatments overtreated with labeled rates of either Fortenza or Dermacor.
Fortenza, from Syngenta, contains the active ingredient cyantraniliprole. In addition, Bateman included an overtreatment with Prevathon, a chlorantraniliprole product from FMC not yet registered for use on rice. Both chlorantraniliprole and cyantraniliprole are diamide insecticides and provide residual control for 60-70 days after planting.
The theory was that by overtreating CruiserMaxx or NipsIt with labeled rates of cyantraniliprole or chlorantraniliprole, the combination would control not only grape colaspis and rice water weevil but also billbugs, which tend to cause damage later than other root-feeding pests.
In the trial, researchers counted blank heads as well as measured yields for each treatment. Statistically, there was no difference in the blank head rating among all treatments.
“One of the things we didn’t capture was the amount of tillers that never headed,” he says. “The untreated check had much fewer heads. I think that’s why we saw the major yield increase. The Fortenza and Dermacor plots probably had twice as many heads but also a high percentage that blanked.”
Currently, Fortenza costs about $7-8 per acre for hybrid seed and $20-22 per acre for conventional seed, according to figures from University of Arkansas Extension entomologist Gus Lorenz. Dermacor is about $12.50 per acre for hybrid seed and $25 for conventional seed. NipsIt and CruiserMaxx both cost about $10-12 per acre for either hybrid or conventional seed.