Dryland farming has never been easy. But in recent years, [Nate] Northrup has been battling a new challenge that would have baffled earlier generations: the wheat stem sawfly. It’s a pest that infests wheat stems at the base, flattening fields — usually just before the harvest. Northrup described a slow progression of sawflies infiltrating his wheat fields, starting in 2010.
“It used to be just a few swaths around the edges,“ he said. “And then, the next year following, it would just be entire fields, just laying on the ground.”
Adult wheat stem sawfly. Photo credit: Colorado State University
Last fall, Colorado farmers planted more than 2 million acres of winter wheat for the 2022 harvest. But persistent drought is hurting Colorado’s crop, and the sawfly infestation only worsens things.
Lodging cause by wheat stem sawfly. Photo credit: Colorado State University
The mature bugs emerge in the spring and lay their eggs in young wheat stems. As the wheat grows, so do the sawfly larvae, eating their way down to the bottom of the plant. Just as the wheat ripens and becomes ready for harvest, the larvae ripen and get ready to hibernate. It makes itself an overwintering chamber just above the root and, in the process, takes a final big bite at the base of the wheat stem, weakening it beyond repair. The first wind or sprinkling of rain topples the weakened stalks flat on the ground.
Dr. Erika Peirce is a postdoctoral researcher at Colorado State University who specializes in integrated pest management of the wheat stem sawfly, which, she is quick to point out, is not actually a fly.
“Contrary to the name. It’s actually a wasp,” she explained. She says sawfly may be a new pest, but the bug is not new to Colorado. “It was initially discovered in non-cultivated grasses – the grasses on the side of the road — in 1874 in Colorado. It only became a pest of winter wheat in Colorado in 2010.”
Peirce says the sawfly’s transformation from benign native insect to threatening pest happened because of a change in its lifecycle. Initially, adult sawfly timed their emergence to align with the growth of the non-cultivated grasses that were its native host. She explained that winter wheat develops earlier in the season than those native grasses.
“The sawfly, in order to use winter wheat, has to mature and emerge about 3 to 4 weeks earlier than they normally would for their native hosts,” she said.
