Wireworm survey of small grain and potato fields in Montana

Wireworms appear to be an increasing threat to the sustainable production of small grains, potatoes and other crops since the delisting of lindane, an effective and inexpensive insecticidal seed treatment. During the spring of 2011 and 2012 we surveyed the complex of wireworm species damaging commercial small grain and potato crops in Montana using canister-type bait traps that we developed in 2010. The canisters were mailed to collaborating producers who buried them in selected crops for10-14 days and then returned them to Montana State University for species identification. In 2011 61 grain fields in 12 counties were evaluated. Wireworms were caught in 18.6% (8/43) of fields with no prior known history of wireworms, but catches in these fields were low, averaging 0.2 to 1.0 larvae per trap. Wireworms were caught in 66.7% (12/18) of fields with a reported history of wireworms, with the most infested field averaging 13.4 larvae per trap (n = 5 traps). The prairie grain wireworm, Ctenicera aeripennis destructor, was thought to be the most common species in the region. Howwever, Limonius californicus, L. infuscatus, Hypnoidus bicolor and Aeolus mellillus were identified as the most common species.  Species often co-occurred in the same field.  During 2012 67 grain fields and 54 potatoes fields were evaluated in 24 different counties.