Wheat Stem Sawfly and Alfalfa Weevil Cause Trouble for Growers

Wheat Stem Sawfly and Alfalfa Weevil Cause Trouble for Growers

July 25, 2013

Two species of insects have been making life difficult for alfalfa and wheat growers this season, a University of Nebraska-Lincoln entomologist said.

The wheat stem sawfly and alfalfa weevil have been reported in higher numbers than last year, said Jeff Bradshaw, entomologist at the Panhandle Research and Extension Center at Scottsbluff.

"We had a fairly warm, mild season last year and the wheat stem sawfly overwinters as a pupa," Bradshaw said. "If it is too warm in the spring, it will just decide to not emerge so it can actually carry over to the next year."

Bradshaw said that the higher numbers this year are partially due to carryover from last year.

The wheat stem sawfly lays eggs in the stem of wheat plants. When the larvae hatch, they damage the stems, causing the wheat to collapse in the field. This can lead to a loss in yield at harvest.

"Not only can you not harvest the wheat, but when that wheat falls to the ground the mature grain can develop, leading to volunteer wheat," Bradshaw said. "The volunteer wheat can be a host of aphids and wheat curl mites."

Due to the nature of the sawfly, it is difficult to control with chemical sprays.

"Not many products get inside the stem," Bradshaw said. One management option would be to "plant a hard-stem wheat in a border area," Bradshaw said. "The sawfly can't completely finish development in a hard-stem plant."

If the problem persists, it may be best to rotate the field to a crop that doesn't host the sawfly, such as corn, sunflowers, dry peas, and some types of barley, Bradshaw said.

For alfalfa growers, the alfalfa weevil damages crops by eating the foliage.

"Alfalfa weevils comes in early in the year during the first cut. The problem we have in western Nebraska is that there seems to be another bump in the population earlier in the season."

Products containing chlorpyrifos can help suppress alfalfa weevils, Bradshaw said.

For more information on alfalfa weevils and treatment thresholds, see the June 21 CropWatch article.

Heather Haskins
IANR News Student Writer