Sorghum and milo planting are well under way in South Dakota, and we are starting to receive reports of stand issues with some earlier planted fields. Upon inspection, these fields were found to have patches where it appeared the seed had been fed on, or the cotyledons had been removed. The culprit of these stand issues was determined to be wireworms (Figure 1).
Wireworms (Click Beetles): Pest Profile
Wireworms are the larvae of click beetles, which are commonly observed throughout the summer (Figure 2). There are many different species of wireworms and they can vary dramatically in both size and color. Wireworm populations are typically larger in fields that are following pasture, CRP, or as we are finding throughout South Dakota, wheat. Wireworms may be an issue for multiple years as some species can persist in the soil for up to three years. Unfortunately, there are no rescue treatments available once wireworms or the injury left by them is observed after planting.
If wireworms are observed throughout the field, options for management include replanting using an in-furrow insecticide or leaving the crop as is. Wireworms typically reduce stands in small patches in a field, and do not remove large areas unless very high populations are present. Although insecticide seed treatments are labeled for wireworm management, there is evidence that they act as a deterrent or repellant and do not actually cause mortality of the wireworms. If a crop is going to be replanted into a field where wireworms previously reduced stand, we strongly recommend the use of an in-furrow insecticide that is labeled for wireworm management in the crop.
Wireworm scouting should occur prior to planting, and consists of placing bait stations in the fields. The bait stations are constructed by digging a shallow hole, and placing pre-germinated corn or wheat seed within. The hole should then be covered using black plastic and marked so that it can easily be found later. Each week, prior to planting, the bait stations should be monitored to determine if any wireworms were attracted to the pre-germinated seeds.