What To Do About Wheat Stem Sawfly?

By Denise Markle, Area Crop Protection Specialist, North Central Research Extension Center, NDSU

Wheat stem sawfly (Cephus cinctus) is native to North America, however it is still a very important insect pest, especially in western North Dakota and Montana. The sawfly infests spring, winter, and durum wheat. It not only causes reduced yield and quality, but also lodging which can make harvest difficult if not impossible.

Female sawflies deposit their eggs directly into the wheat stem. The mature larvae cause damage by chewing a notch around the inside of the stem which often results in lodging. Current management practices for the sawfly are limited. Insecticide treatments are often ineffective because the egg and larva are protected in the stem. It is also difficult to reduce the adult sawfly population due to its extended emergence. Because each female lays eggs in multiple stems, and multiple females lay eggs in a single stem the adult population must be reduced at least 90% before there is a reduction in infested stems. Solid stemmed varieties are less susceptible to sawfly infestation and less likely to lodge. However, many solid stem varieties do not yield as well as the hollow stemmed varieties (in the absence of sawfly).

Research was initiated in western ND in 2008 to expedite development of higher yielding solid stem varieties and to further investigate the potential of using an insecticide to control wheat stem sawfly. Eleven wheat varieties, including solid and hollow stem varieties, were evaluated at Scranton, Regent, Hettinger, and Williston, ND. Although severe drought conditions significantly impacted yields, Vida (semi-solid) and Agawam (solid stem), were among the highest yielding varieties. Hollow stem varieties evaluated included Steele-ND, Reeder, Howard, and Glenn. This research will be continued in 2009 to further evaluate the varieties in different environments.

Insecticide studies were also initiated in Hettinger, and Makoti, ND. Treatments included 1) untreated check, 2) foliar insecticide at the 4-6 leaf stage, 3) foliar insecticide at flag leaf stage, 4) low rate of insecticide seed treatment, 5) high rate of insecticide seed treatment, and 6) low rate of insecticide seed treatment + foliar spray at the 4-6 leaf stage. The number of infested stems was not significantly reduced regardless of treatment at either location. However, at the Hettinger location there was a trend for reduced infestation with the high rate of seed treatment, and the flag-leaf application of insecticide. This may be due in part to a lower sawfly population in Hettinger compared with Makoti. This research will be continued to determine if there is an insecticide treatment that will effectively control wheat stem sawfly. Until an effective treatment is determined, insecticide use is discouraged to conserve beneficial insects that are parasitoids of the sawfly.