Wheat Stem Sawfly Damage Leads to Downed Wheat - UNL CropWatch, July 29, 2011

Wheat Stem Sawfly Damage Leads to Downed Wheat - UNL CropWatch, July 29, 2011

July 29, 2011

When I first moved to Scottsbluff, a retired gentleman who volunteers at the Farm and Ranch Museum (Gering) told me, “It would be paradise out here if not for the wind and the hail.”

Wheat damaged by wheat stem sawfly

Lodged wheat in a field near McGrew caused by damage from the wheat stem sawfly. Damage develops when, at the end of its larval lifecycle, the sawfly larva girdles the wheat tiller just around the first node above the wheat crown, making it vulnerable to wind pressure.  (Photo by Drew Lyon)

After just a short time of living here, I can confirm that the wind and the hail can be quite severe. This is all too obvious when the damage flattens acres of previously lush cropland. With the degree days accumulating quickly, producers have been scrambling to harvest their wheat fields (at least those not pounded by recent hail). In some areas it’s been surprising to see stands knocked down by the wind, with affected areas concentrated along field edges. What could have caused this? I suspect the wheat stem sawfly.

This year, the wheat stem sawfly has been abundant and widespread. In fact, it was reported for the first time over numerous fields throughout
eastern Colorado.This represents a significant expansion southward for
this insect.

Wheat damage develops when, at the end of its larval lifecycle, the sawfly larva girdles the wheat tiller just around the first node above the crown. This weakens the upper portion of the wheat stem (and the wheat head), making it vulnerable to high winds.

Recently Drew Lyon, extension dryland cropping systems specialist at the Panhandle REC, reported that a field near McGrew had 50-80% yield loss due to lodged wheat resulting from wheat stem sawfly damage (Figure 1). Due to repeated, similar sawfly damage, a Harrisburg farm couple indicated that they may no longer grow their usual 1,500 acres of wheat.

Management

Sawfly management options are quite limited because no insecticides are effective against this insect and the only varietal resistance is from hard-stemmed wheat varieties, which have low yield characteristics. The only management practice recommended in the past was tillage.

Research

This summer I have been working on a project with Susan Harvey, a research technician at the Panhandle REC, to map the distribution of this insect in Nebraska as well as the distribution of the parasitoids that attack the wheat stem sawfly. We are also noting the management practices used in our sampled fields. This project is partially funded by USDA. Our hope is that we can understand what production practices might favor the parasitoids that attack the wheat stem sawfly. I will keep you up to date on our findings via future articles in CropWatch.

Jeff Bradshaw
Extension Entomologist, Panhandle REC