06 Aug Megan: Sawfly Sorrows
Hemingford, Neb. – Aside from the recent rain, there has also been another interesting problem we have encountered around Hemingford. Working on harvest I have become very familiar with certain complications of growing wheat such as: rye, jointed goatgrass, rust, sucker heads, etc. However, this year I have been exposed to a new term: sawfly. Wheat stem sawfly is a native grass-feeding insect, about ¾ inch long, that feeds upon the wheat stem, causing it to break. A recent article by the Institute of Agriculture and Natural Resources at the University of Nebraska – Lincoln explains about the wheat stem sawfly sensation that has manifested much of western Nebraska’s wheat. Jeff Bradshaw, an entomologist (a specialist in insects)in UNL’s Department of Entomology reported, “We had a fairly warm, mild season last year and the wheat stem sawfly overwinters as a pupa. If it is too warm in the spring, it will just decide to not emerge so it can actually carry over to the next year.” Bradshaw stated the high numbers of sawfly this year is partially carried over from last year.
The cycle of wheat stem sawflies begins when they lay eggs in the stem of wheat plants. Upon the larvae hatching, they damage the stems by girdling the wheat stalk. This weakens the upper portion of the wheat stem, making it vulnerable to high winds and often causing the wheat to collapse. When the wheat becomes lodged due to this, it makes it very challenging for the combines to harvest the fallen wheat, which can negatively affect yields. Bradshaw explains, “Not only can you not harvest the wheat, but when that wheat falls to the ground the mature grain can develop, leading to volunteer wheat. The volunteer wheat can be a host of aphids and wheat curl mites.”
This is a diagram from the UNL Plant Breeding Training Network explaining the life cycle of a wheat stem sawfly. For more information, visit http://passel.unl.edu/communities/pbtn?idsubcollectionmodule=1130274157&idindependentpage=251
A view from the side of a wheat field that has been damaged by wheat stem sawfly.
Dad picks up the fallen wheat stems caused by sawfly. It literately looks like someone has cut off random wheat stalks and let them fall to the ground.
Looking down between rows in a wheat field. All of the fallen wheat is from sawfly damage and is near impossible to pick up with the combines.
Statistically speaking, one wheat head loss per square foot is equivalent to a bushel to the acre loss. This means that by not being able to pick up just one head of wheat within a square foot, the yield is affected by at least a bushel per acre less.
Even after being harvested, many wheat stalks remain on the ground due to sawfly. Dad estimates the sawfly has affected about 10 to 20% of the fields in the Hemingford area.
So what are farmers to do about this problem? Actually, management of sawfly is rather limited due to the lack of insecticides that are effective against them. The only known resistance from sawfly is planting hard-stemmed wheat varieties, which commonly have low yields. It has been suggested that swathing and windrowing the wheat while it is still somewhat green at the end of June could be beneficial. By doing this, it would cut the wheat before the sawfly has the opportunity to cut it. However, this requires twice the time and money to harvest the wheat since the windrows will have to be picked up after they have dried out. Futhermore, my brother-in-law, Kurt, mentioned that sawfly is a well-known issue in northern Montana, where he grew up. They have found sickle pickup guards or crop lifters to be helpful in harvesting the lodged, damaged wheat from sawfly.
Bottom line: The only management practice that is currently recommended to reduce sawfly is tillage. Research continues to find other options to eliminate wheat stem sawfly. In the meantime, as harvesters we do our best to cut as low as possible to pick up as much lodged wheat as we can. This is a tricky process since many farmers in the area practice no-till farming and would prefer taller stubble to catch snowfall in the winter.
This is a photo from the Colorado State University (CSU) extension office. On the left is an adult wheat saw sawfly and on the right is sawfly larva in stub. (I apologize for the photos being slightly blurry, but these were the best ones I could locate.)
These are photos by Gary Hein, Susan Harvey, and Jeff Bradshaw from the University of Nebraska – Lincoln (UNL). On the left: Darkened areas develop on the stem where the heaviest wheat stem sawfly feeding occurs. On the right: The most severe damage is visble at the end of the growing season after larvae cut stems to form pupal chambers, resulting in lodged wheat.
All Aboard Harvest is sponsored by High Plains Journal and Syngenta. Megan can be reached at firstname.lastname@example.org.