Wheat stem sawfly causes $30M in damages to local agriculture

Wheat stem sawfly is a native insect that feeds on grasses in Colorado. The insect was first identified by entomologists in Colorado around the late 1800s and primarily fed on range grasses. However, wheat stem sawfly emerged as a Colorado wheat pest in 2010 and damage from this insect has been expanding and increasing since. Today, this pest is estimated to cause $30 million in damage, according to Brad Erker, executive director of the Colorado Wheat Research Foundation. As a result, Colorado State University is focused on addressing cropping strategies to ease pest losses to this insect. Research is focused on cropping rotations, and developing wheat varieties that discourage wheat stem sawfly from reproducing and damaging plants. 

Colorado State and others have found that wheat stems that are more solid than the traditional hollow-stemmed varieties have shown merit in reducing the pest’s damage. Typically, adult wheat stem sawfly lay eggs in the stem during the growing season. The developing larvae feed and move downward in the plant, and eventually cut the plant’s stem off near the soil surface. The wheat plant with seed in heads fall to the ground and are un-harvestable. Thus, not only is yield impacted negatively, but straw residue is also now laying flat on the ground. The larvae survive in the remaining stem near the soil surface. 

Cropping strategies include shallow tillage that lifts wheat crowns and loosens soil. This activity exposes larvae to winter weather and increases mortality during some winters. However, tillage interferes with biological control insects (insects that feed on sawfly) and may increase soil erosion. Keep in mind that the advantages of controlling sawfly with tillage must be compared to the benefits of leaving residue on tops of fields. 

Another strategy for tolerating wheat stem sawfly is to swath wheat early. Swathing wheat at 25-30% moisture allows wheat to reach physiologic maturity and permits harvest before sawfly cuts plants off. This strategy necessitates the use of a swather to windrow wheat, allowing grain to dry in the swath, before stem cutting has occurred. Swathing before grain is 30% moisture will cause test weights to drop as plants are still filling grain. Wheat stem sawfly will still cut stems after swathing, but losses to yield will be reduced as grain will remain harvestable in the swath. 

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