By David Crowder, Washington State University entomologist
With spring planting just around the corner, producers should be considering their management approach towards wireworms and other insect pests.
Wireworms, which have larvae that can feed in the soil for 2 to 11 years (depending on the species), are one of the primary direct pests in Washington wheat crops. However, wireworms are a complex of species, and management should be tailored to the specific species present on a farm.
In eastern Washington and northern Idaho, the two dominant wireworm species are the western field wireworm, Limonius infuscatus, and the sugarbeet wireworm, Limonius californicus. Of the two species, the sugarbeet wireworm is by far the most damaging. If this species is present in fields, our research has shown that increased rates of neonicotinoids provide more effective and economic control. In contrast, the western field wireworm is often not a damaging pest.
Our research has shown that low rates of neonicotinoids are typically sufficient for control of this pest in wheat. Our results from the past two years also suggest that neonicotinoid treatments do not increase yields of barley or oat crops, regardless of the wireworm species present. While we do not yet fully understand why these cereals appear to be more tolerant of wireworm feeding, producers may want to reconsider the use of neonicotinoids on these crops.
When soil temperatures reach 45 F, we recommend that producers use bait traps to sample for wireworms in their field and use trap catch to identify wireworms present. The species present in a given field are typically consistent from year to year, and this information can be used to make proactive management decisions.
Our project team continues to investigate novel management approaches for wireworms, including biological control and the application of insecticides in rotation crops (i.e., peas). Until new control options become available, however, tailoring wireworm management to the specific species present in a field represents the most economical option for producers.
For those with high wireworm populations, delayed seeding of the most infected parts of fields has also been shown to be an effective strategy for managing wireworms in wheat crops.