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New Field Pea Insect Pest in SW ND (06/22/17)

Pea leaf weevil (Sitona lineata L.) was found in Golden Valley and Stark Counties last week during a field trip to determine if this insect is established in field peas grown in North Dakota.

New Field Pea Insect Pest in SW ND

Pea leaf weevil (Sitona lineata L.) was found inknodel.1 Golden Valley and Stark Counties last week during a field trip to determine if this insect is established in field peas grown in North Dakota. Leaf feeding notches and larvae were found feeding on the root nodules of field pea in both counties. This is an important insect pest of field pea, and is established in Virginia, Florida, California, Washington, Oregon, Idaho, Montana and now southwest North Dakota in the U.S. In Canada, it is found in British Columbia, Alberta and western Saskatchewan. Pea leaf weevil in native to Europe, Asia and Africa. It was introduced to the east and west coast of U.S. in the 1920’s.

Further survey work will be conducted this summer through the IPM Survey, NDSU Extension Program, to determine the extent of its range. We would appreciate any new sightings (and samples) of larvae or adults. We would need actual samples of larvae or adults to confirm its identification and presence. NDSU Extension Service will be publishing a fact sheet with more information in the near future.

Here is a summary of our observations from the field trip:

 

  1. Early adult pea leaf weevil feeding was confined to the earliest leaves (lowest on the plants). The feeding notches are rather regular and symmetric around the leaf margins, and the notches are small (about 1/8”), deep semicircles (see photograph). Cutworm/grasshopper/other insect feeding notches are not as regular and symmetric, wider and/or shallower. The presence of these notches is a good field symptom that pea leaf weevil may be present.
  2. In infested fields, it was easy to find larvae feeding in the root nodules. Now is the time to look for larval feeding in root nodules of the pea plant. Dig plants with pea leaf weevil feeding notches. Carefully remove soil and examine the nodules for larvae and feeding injury. Larvae are 1/16 – 1/8” long, C-shaped, milky white with a dark brown head capsule (see photographs). Larvae actively feed on and in the nitrogen-fixing nodules. You will need a hand lends or may want to bag pea plants and then look at nodules under a dissecting microscope in lab. Larvae cause most of the economic damage to the pea plant by feeding on the nitrogen-fixing nodules, which reduce the level of nitrogen available for the crop and can decrease yield.

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  1. Pea leaf weevil was observed at 80% incidence of leaf notching near Beach and Golva in Golden Valley County and only 10% incidence of leaf notching near Dickinson and Gladstone in Stark County. We believe that pea leaf weevil has likely been in Golden Valley County for several years, and in Stark County, it is just getting established. Reports from Montana indicate that pea leaf weevil is moving eastward. The detection in southwest North Dakota support this, as Beach is 250 miles east from the nearest known infestation in Lewistown, Montana.
  2. It is too late for effective control measures this year. Pea leaf weevil is managed in the spring when adults emerge from overwintering sites. The main pest management tool is insecticide seed treatments or foliar insecticide treatments applied at a treatment threshold of 25-33% leaf notching.

 

Janet J. Knodel and Patrick Beauzay

Extension Entomology

 

Ryan Buetow

Area Extension Specialist/Cropping Systems

NDSU Dickinson Research Extension Center

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