Timing of injury and efficacy of soil-applied insecticides against wireworms on potato in Virginia

Wireworm control has become a major pest management concern for potato growers in the United States. Studies were conducted from 2002 to 2005 on the Eastern Shore of Virginia to identify the species complex of wireworms and timing of injury to potatoes, and to evaluate the efficacy of various soil-applied insecticides alone or in combination for wireworm control. The cornfield wireworm, Melanotus communis (Gyllenhal), was the dominant species found in potato fields accounting for roughly 80% of individuals collected. Conoderus lividus De Geer and Conoderus vespertinus (Fabricius) comprised the remaining 20% of wireworm specimens found. Wireworms were most apparent on or near potato seed pieces in late April, and were detected less frequently near potato plants over time as the season progressed into July. Most wireworm damage to potato tubers, however, occurred late in the potato crop season (after mid-June). There was a significant positive relationship between tuber size and percentage of wireworm damage. In general, the longer tubers remained in the ground, the higher the percentage of wireworm injury.Results from several insecticide efficacy experiments in potatoes showed that fipronil, imidacloprid, thiamethoxam, and bifenthrin applied to the soil at planting provided similar wireworm control (50–80%) to that of the organophosphate standards, phorate, and ethoprop. Combinations of imidacloprid or thiamethoxam with fipronil or bifenthrin did not enhance the efficacy of any one of them used alone. The aforementioned products provide much needed alternative insecticide modes of action for wireworm control in potatoes and perhaps other crops in the future.