CONRAD, Mont. – In the Golden Triangle region of Montana, where producers are incorporating pulses into their rotations, fighting the pea leaf weevil and the pea aphid are vital.
“Montana is the number one pea and lentil growing state in the nation,” said Dr. Gadi V.P. Reddy, entomologist of Montana State University’s Western Triangle Agricultural Research Center.
“For pea growers, pea leaf weevil grubs are highly economically damaging because the larvae feed on roots, resulting nitrogen, and other nutrients not available to the plant.”
There are several reasons Montana producers choose to incorporate peas, lentils and chickpeas in their rotations.
“We’re growing so many pulses partly because we needed alternative crops in our wheat rotations to break up disease and insect life-cycles,” Reddy said.
Producers in the Triangle and in the rest of the state also are receiving better prices for pulse crops, and many are finding contracts with pulse receiving and processing facilities in Montana.
“Prices have been good, especially for lentils, and growers have been finding contracts from commercial firms, because so many markets in the world have been buying pulses,” he said.
Peas, lentils and chickpeas are consumed in the Asian countries in large numbers for specific foods and the markets need a lot of pulses for exporting.
Insects, such as pea aphid and pea leaf weevil, have invaded pulse acres, and are damaging pulse acres.
“The pea leaf weevil has been a traditional pest for many years, and there is a lot of these pests in Canada,” he said.
The pea leaf weevil adults feed on the leaves, but don’t cause much damage. During winter, the weevil hibernates under debris leaves and emerges in the spring, usually around May.
When the pest emerges in spring, the adults feed on pollen and nectar on leaves; then they mate and the females lay eggs on the seedlings of peas and lentils that emerge as larvae.
Larvae or grubs burrow deep in the soil and feed on roots and root nodules, causing damage. Plants fix less or no nitrogen when the roots are damaged, and sometimes the plant itself dies.
“The pea leaf weevil spread across the pulse growing regions in 2012, increasing problems caused by the pest,” Reddy said.
There are two generations of pea leaf weevil per year, but the second generation of adults does not cause damage like the first generation. Second generation adults don’t mate but they do hibernate during winter.
Reddy applied for grant funding under the Montana Specialty Block Grant program, in cooperation with the Montana Department of Agriculture and USDA-National Institute of Food and Agriculture (NIFA), for the pea leaf weevil pheromone project to attract the pea leaf weevil.
“The pheromone compounds have been identified in the UK, but they weren’t optimized on how we could use them in the field,” he said.
Reddy was funded to work on the pheromone project - to use baited aggregation pheromone traps in the field to help in monitoring and mass trapping the weevil population.
Pheromone traps they tried were pitfall, ground, delta and ramp tramps, but the best at catching pea leaf weevils was the pitfall trap.
“The traps are like a pit-fall trap that stays in the soil. We use a liquid aggregation pheromone lure to the traps to attract the adults and they fall in the pit,” he said.
A pitfall trap is a container that is sunk into the ground so that its rim is flush with the soil surface. Insects are captured when they fall into the trap.
Another pheromone lure type is a bubble wrap, placed in pea or lentil fields.
In these traps, they use a small quantity of soap or detergent water so that the trapped weevil gets killed. Consequently, there would be no eggs and emerging larvae to damage the roots.
“We found a lot of pea leaf weevils in our pheromone traps in 2016. Next summer, we will determine how many pheromone-baited traps we need per acre to trap the weevils,” he said.
In addition, WTARC will be developing biodegradable pheromone lures so that growers will have no need to take them out after each season.
Pea fields are the most attractive to the pea leaf weevil, and lentils are less attractive to the weevil.
In addition to soap and water, producers could use a small quantity of liquid insecticide that would kill the adult weevils. Alternatively, the growers can use Hercon Vaportape (insecticidal strip) in the pheromone traps as this product is registered with the Environmental Protection Agency.
“Producers only need a very small amount, so the insecticide is not expensive,” he added.
Reddy is also looking at bio-based insecticides to control pea leaf weevils.
“We are doing some significant research work on ridding the pea leaf weevil in Montana,” Reddy said.