As rice begins to head in Arkansas many producers are checking fields for rice stink bug, but their sampling technique could be costing them money.
While working on an improved treatment threshold—which indicates the density of insects per square foot—for rice stink bug, Aaron Cato, doctoral entomology candidate at the University of Arkansas came to the realization that past researchers and the public haven’t been on the same page when it comes to sweeping techniques.
Rice stink bug is a problem because it feeds on rice kernels causing direct yield loss, and can also cause a quality loss called peck.
Rice stink bug research bases its treatment thresholds on insects captured during 180-degree sweeps, meaning the sampler swings the sampling net a half-circle from right to left, rotating at the waist.
These elaborate sweeps are physically tiring and not ideal for consultants covering a multitude of acres. Also, new cultivars of rice make the field dense with larger plants and that density means a scout will have to put more oomph into each arc.
“Previous research has used a complete 180-degree sweep to base thresholds on,” Cato said. “But with the high-yielding rice we have today, especially hybrid rice with increased tillering, if you try to walk at a decent pace while sweeping that wide, you’re going to stumble. No one in Arkansas that we’ve talked to follows that method, so everyone’s working with samples smaller than what we base our thresholds on.”
Looking at what will work
Thus began a study to find a sweep that was less taxing, but still wide enough to get an accurate sample. It’s information that Gus Lorenz, extension entomologist and associate department head of Entomology and Plant Pathology for the University of Arkansas System Division of Agriculture, says could mean money in the bank for Arkansas’ rice growers. Lorenz is also Cato’s major advisor.
“Aaron is refining decision-making for rice stink bug control in Arkansas,” Lorenz said. “His research could save Arkansas growers literally millions of dollars by saving unnecessary insecticide applications, while still maintaining yield and quality.”
However, sweeper variability plays a big role in whether or not Cato’s recommendations will translate to the samples being taken by the public.
“By reducing sweeper variability we can be sure we’re comparing apples to apples, not apples to oranges,” Lorenz said.
Trying a trio of techniques
Cato’s work tested three separate sweeping techniques and compared the results.
“We looked at 6-foot sweeps and 3-foot sweeps and compared them to the 180-degree sweeps,” Cato said. “We found that the 6-foot sweeps are very accurate in the amount of stink bugs you’re going to catch. So you can still do a set of 10 samples of 6-foot sweeps, and get an accurate depiction of how many stinkbugs are across the field.”
Sticking with a 6-foot sweep length can keep samples accurate, but not at the expense of a sampler’s energy level. Cato also recommends keeping other factors in mind.
Additional factors
Pace: Samplers should get 1 to 2 feet of space between each sweep.
“When you’re sweeping be sure you’re taking at least one step, maybe multiple, at a good pace so you’re not sweeping the same area twice,” Cato said. “If you’re hitting rice that’s just moved from your last sweep you’re going to be taking a bad sample.”
Net placement: Sweep nets should pass through the center of the rice heads. Sweeping too high or too low can cause inaccuracies.
“You want to be sure the hoop of the sweep net encompasses the center point of the rice heads,” Cato said. “If you’re too low and you’re hitting under the rice heads, you’re going to launch the stink bugs off of it. If you’re too high you’re going to knock them down into the water. No matter if it’s too high or too low, you’re not going to catch everything that’s there and you’re going to take a bad sample.”
Net angle: Sweep nets should be slightly angled so that the top of the hoop faces up and slightly rearward.
“You want your net to be angled back a little bit so that when it does hit the rice, the rice kind of tips over into it and the stinkbugs will fall into the net,” Cato said. “If you do it straight up and down it’s possible they’re falling out. If it’s angled downward you’re going to be knocking stinkbugs into the water.”
For more information on pest control in rice contact your local county agent or visit uaex.edu.
