The wheat stem sawfly has begun emergence throughout the High Plains. Observations from several locations – the High Plains Ag Lab (HPAL) near Sidney, Neb., the U.S. Department of Agriculture Agricultural Research Service (USDA-ARS) Research Station near Akron, Colo., and as far east as Deuel County, Neb. – indicate very high populations of wheat stem sawfly in wheat fields.
Additionally, walking through wheat fallow fields one can also find wheat stem sawflies flitting around the residue, regardless of what the annual crop might be. This is because the wheat stem sawfly survives from mid-July of the previous year through May in the pupal stage within wheat residue left behind from the previous harvest.
Observations last week at HPAL indicated that sawflies might be emerging from deep within fallow fields and not just emerging from field edges. This pattern of emergence suggests a very large population at that location. This is certainly not good news for wheat producers in the southern Panhandle who witnessed striking wheat lodging in some fields last year that resulted from heavy sawfly infestations.
The silver lining, at least for HPAL, is that as a test site for the State Variety Test (https://cropwatch.unl.edu/varietytest) we will have an opportunity to compare wheat varieties under high sawfly infestations.
Similar visual observations of lodging were reported last year. This may help “ground truth” current sawfly-resistant varieties as well as help us gain new insights into sawfly resistance. Additionally, the Small Grains Breeding Program at UNL has sawfly resistance as one of their primary breeding objectives.
Tillage practices and parasitoid conservation efforts may play a role in affecting the populations dynamics of wheat stem sawfly populations. Articles on these topics can be read at Nebraska Extension’s CropWatch website; search for the keyword “sawfly.”
What can a wheat grower do now? Growers who believe that infestation in their fields will result in losses close to or below their crop insurance guarantee should turn in a probable-loss claim with their crop insurance agent now.
However, from a production standpoint there is not much they can do. Later articles will discuss options for producing wheat under threat from the wheat stem sawfly.
Right now the best tool a grower has is information. We recommend trying to gather information about which acres seem to have the highest sawfly infestations and be timely in harvesting heavily infested fields. As wheat fields begin to ripen, consider cutting some handfuls of wheat at a few locations across your wheat fields. Split 25-50 handfuls of tillers and observe any tillers with frass or “sawdust” within the tillers. No other insect that infests wheat will leave behind frass within the tillers, which will otherwise be mostly hollow (unless you planted a solid-stem variety).
Take notes on where and in which fields sawfly infestations were found. This may provide insight for what to do this coming fall or spring to manage fallow for sawfly, or help make decisions for variety selection or winter crop choice for this fall.
Growers can help IANR researchers learn more about wheat stem sawfly in our region by sharing their sawfly observations with us, so please send your field updates to Jeff Bradshaw (firstname.lastname@example.org) to help us learn more about wheat stem sawfly infestations. Notes will be compiled and shared back out with the IANR dryland cropping systems community this fall.
Watch for updates this summer in the news media, CropWatch website (https://cropwatch.unl.edu) and Panhandle Center website (https://extension.unl.edu/statewide/panhandle/ as we keep track of the progression of this very important wheat pest and as we hopefully are able to glean some additional information to report from this year’s infestations.