We have watched their quick descent into Colorado over the years and now Wheat Stem Sawfly is active in most areas of the Central and Northern Hard Red Winter Wheat growing region. The damage done by infestations continues to be a problem for producers already facing tight margins. Stem breakage and lodging from feeding presents itself right before harvest, and the damage can range from 10-20% yield loss from lodging and around 30% loss from physiological damage. In fields with extremely high numbers of the pest, these numbers can raise exponentially. An integrated pest management system is needed to keep sawfly numbers manageable and minimize risk of crop loss.
To learn how to manage Wheat Stem Sawfly properly it is important to understand them. No, I am not referencing their individual personalities, I’m speaking on how they operate biologically. The life span of these pests is not exceptionally long, with adult males living up to 3 weeks and females living 1-2 weeks. To reproduce they must clear an area in the stem to lay and hatch their eggs. Once the larvae are hatched, they feed along the inside of the stem causing loss of kernels. They eventually weaken the stem enough that it will lodge or break off completely which makes harvest difficult. Over the course of thirty days the larvae feed and eventually make their way to the base of the plant where they seal themselves off for the winter.
Sawfly damage can be hard to detect without examining the stem, until right before harvest. Staggered maturity dates and harvesting before the grain is dried past 14% can help get the crop out of the field before the stalks become too brittle. After 12% moisture the sawed stem is more likely to fall over making it nearly impossible to harvest the heads correctly. Sawfly larvae can be detected by pulling a stem and cutting vertically down the stem. Once the stem is opened you will see a sawdust like substance and possibly some saw fly larvae. This larva will be ‘S’ shaped. The larvae are cannibalistic, so what might start out at 30-50 pests quickly turns to one survivor in each stalk. The surviving larvae will move down the stem to the root system to overwinter.
Sawfly’s habitats include other cereal grains and grasses where they overwinter and then fly a short distance to lay their eggs. They are not exceptional flyers, so crop rotation and transitions between wheat and grass can be enough to deter them; therefore, damage is particularly high along the edges of fields. Tillage, especially shallow tillage, has shown a reduction in sawfly survival by disrupting the roots, making winter survival difficult under harsh conditions. Biological controls using parasitic wasps has also been tried but have not been used much in the United States.
An important tool that has shown tolerance to sawfly is in the wheat plant itself, specifically, solid, and semi-solid stem varieties that can deter the sawfly from laying their eggs or stand up to the pressure of feeding. Sawflies are not the most resilient pest we see on the farm, so they cannot exert too much energy trying to find a suitable place to lay their eggs. Solid stem varieties such as WestBred 4483 and semi-solid straw in the WestBred 4418 and WestBred 4595 have shown tolerance to moderate sawfly pressures. An investment in these certified seed varieties could be the difference between a fair stand or high losses. At a 25% loss of yield on a 60-acre field in these higher commodity markets you could be looking at upwards of a $90 loss per acre.
These varieties do not just offer a tolerance to wheat stem sawfly; they also continue to perform well for your farm. There are now several varieties from various breeding programs approved for the Central Plains region. WestBred offers semi-solid and solid stem varieties and PlainsGold is experimenting with several semi-solid lines that have shown tolerance to Sawfly pressures while still offering good agronomic packages and end useability. Anyone with a concern regarding Sawfly on their farm would benefit from contacting your seed representative to discuss your options.