SUPPORTED BY ENDORSED BY 38 / SEEDWORLD.COM JUNE 2018 agricultural use was banned internationally in 2007.” Other reasons contributing to increased wireworm popu- lations include changing cropping practices. No till rotations, some erosion con- trol techniques and the use of CRP land provide favorable wireworm habitat. “Wireworms are a problem in the Pacific Northwest and are beginning to be a prob- lem in other wheat growing regions,” says Stamm. “It is unclear whether this per- ception is due to an actual increase in wireworm popula- tions problem, or because we are becoming more aware of wireworm damage.” Stamm also notes that in North and South Carolina, farmers are bringing CRP land into sweet potato production where growers are seeing substantial wireworm damage. Cover crops improve conditions for wireworms by providing an improved food source. “Anything which improves soil condition also improves conditions for wireworms,” Wanner says. “A cover crop used for erosion control and then tilled or burned before planting is going to have a lot of decomposing organic matter that will be releasing a lot of CO2 . This will draw wireworms toward the top soil layer. Growers need to consider how to manage the cover crop along with the economic crop they will be planting.” While climate change and changing spring weather patterns have been credited (or blamed) for many environ- mental changes, these are not affecting wireworm popula- tions. Except for drought; in arid regions wireworms still need some spring moisture to come up and feed. “Because wireworms are below ground pests, we do not see anything in this spring’s weather that should concern us,” says Belles. “In areas where there is pro- longed standing water due to heavy rains, the wireworms will not come to the surface because there is less oxygen in the soil. But as soon as that water goes down, they will come up and begin damaging crops.” As weather affects soil conditions, the environment for wireworms is also affected. When soil temperatures reach to 50° F (10° C), wireworms become more active. There are no rescue treatments after the crop has been planted. If there is any upside to dry, hot soil as in a drought, it may be that in these conditions wireworms migrate down into cooler soil and cause less crop damage. Because wireworms are below ground pests, they are well protected from potential predators. The most likely predation is to eggs on the surface. There are few if any native diseases that affect wireworm It is not known if wire- worms have developed any pesticide resistance — their lifecycle and underground habitat make researching this question extremely difficult. There is considerable genetic diversity among wire- worms which means a single chemistry will most likely be unable to completely control these diverse pests. In one project, researchers docu- mented a wireworm survived six months after being intoxi- cated by a chemical pesticide. It had stopped feeding and then recovered. In the short run, this was good for the crop as the wireworm became inactive, giving the crop a chance to become estab- lished. In the long run, how- ever, it was bad news because the larvae was still there and could continue to survive into the next season. Soil is not always a favora- ble environment in which to live for five to seven years. Over time, wireworms have adapted to survive in a wide range of unfavorable envi- ronments. This evolution has made wireworm larvae into a resilient and difficult to kill foe of crop production. Its per- sistence has not gone unno- ticed by pesticide developers. Products are in the devel- opmental pipeline that may eventually provide a measure of control. SW Economic Thresholds for Applying Seed Treatment Wireworms per trap Risk of damage Recommendation (1) 0 Low No treatment 0-1 Moderate Maybe 1-2 Probable Recommended rate 2-4 High Recommended rate >4 Extreme High rate (2) (1) rate of insecticidal seed treatment (2) also consider higher seeding rate and delayed planting WHERE ON THE WEB For more information on wireworms, check out the webinar at: strategy-webinar-podcast/