SCOTTSBLUFF, Neb. – A project getting underway in earnest this year has the potential to address a serious pest threat to dry bean growers.
Dr. Jeff Bradshaw, entomologist with the Panhandle Research and Extension Center in Scottsbluff, is working on ways to deal with the western bean cutworm, a pest that experienced something of a population explosion over the past decade or more. It’s an unusual critter, Bradshaw said, for several reasons.
“It’s called a cutworm, but, unlike a lot of other cutworms, it doesn’t cut,” he said. “The western bean cutworm is an oddball. It feeds on the grain.”
The western bean cutworm hails from the same biological family as other cutworms, which typically infest and feed on seedling crops in the spring. The western bean cutworm is a late-season pest, particularly attracted to tasseling corn and to the new pods in dry beans, Bradshaw said.
“In both corn and dry beans, the damage comes from (larva) feeding on the corn kernels or, in the case of dry beans, actually feeding on the pods, and then the beans inside the pods.”
Up to now, dealing with the western bean cutworm has been a fairly straightforward proposition. Researches across the region use pheromone traps to get counts of the adult western bean cutworm moths as they begin their mating flights in early- to mid-July.
When those numbers reach large enough levels in a given area, agronomists, crop specialists and producers can call in aerial applicators to douse the developing larva with insecticide and, hopefully, avoid the damage to their crop. All the numbers are available through two University of Nebraska Extension websites: cropwatch.unl.edu, which is updated weekly throughout the growing season with a variety of information and data, and entomology.unl.edu/agroecosystems/western-bean-cutwork-central, a website focused specifically on western bean cutworm populations and tracking.
But, as extensive as the network tracking the moths is, there’s still a couple of drawbacks, Bradshaw said.
“Moth counts in pheromone traps only indicate the number of males,” he said.
Those numbers can be used to estimate the number of egg-laying females. But neither vector of the pest is the one that causes the damage, and no amount of data can replace visually scouting a field to see if western bean cutworm egg clusters are present, Bradshaw said.
One typical way of addressing insect pests in crops is through the use of insecticides, often done in several applications, both pre- and post-emergence. But one problem with that is, if applied at the wrong time, insecticides can actually make the problem worse by killing off beneficial insects, known as generalist predators, which feed on the pest insects, keeping their numbers down to where the economic impact is minimized.
“We had some producers tank mixing insecticide with their first post-emergent applications,” Bradshaw said. “You’re clearing the field of any potential (generalist predator) control measures you might have and setting yourself up to possibly higher risk that first week of August. They may end up having to come back again with an application to address a population that never would have exceeded threshold in the first place, had you never treated early in the season.”
And that’s where Bradshaw’s new project comes in. He got interested last year, wondering what could be done to actually boost the number of generalist predators in dry edible beans so enough are around when the western bean cutworm larvae hatch and begin feeding.
“What if we do a relay crop of winter wheat and dry beans?” Bradshaw asked. “There’s a lot of interest in cover crops – what if we took that a step further.”
The idea is simple: In the fall, plant a normal winter wheat crop with full intention of harvesting it for grain the following summer. Then, in the spring, go back across the same field and plant dry beans. The wheat still acts as a cover crop, helping with weed control, with the added economic advantage of providing a mid- to late-summer grain crop. Plus, once the wheat is harvested, any generalist predator insects feeding on thrips or other wheat pests would move straight into the dry beans, just in time to feast on western bean cutworm larvae before they can damage the beans.
“You harvest that wheat over those dry beans, where are all those predators going to go?” Bradshaw said. “Right into the dry beans.
“Now, the predators are looking around for something to eat, corn is tasseling, western bean cutworm moths are coming in, eggs are getting laid and, bam.” He said. “They get lit up by those generalist predators – It’s buffet time.”
Exactly how effective those predators will be in controlling the western bean cutworm is just one of the questions Bradshaw hopes to answer. He’s only done one, small-scale test – more as a proof of concept than anything else – last year. This year, the real research work begins.
What are the seeding rates for the wheat? For the dry beans? Do you plant on 15-inch rows or 30-inch? Do you plant beans with the rows of wheat or across them?
“There’s still a lot of things to figure out,” Bradshaw said. “I think the idea, the nugget of it, is intriguing. What if you could get two crops in one season? And reduce your input costs? And improve conservation bio-control?
“This project has this beautiful connection between aspects of basically ecology and things scientists who don’t do actual field work in agriculture would be excited about. At the same time, it’s meeting, I think, some very specific needs for our producers.”