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 percent to 80 percent 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.
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.
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.