Population Responses of Potato Leafhopper (Hemiptera: Cicadellidae) to Insecticide in Glandular-Haired and Non-glandular-Haired Alfalfa Cultivars.

Conflicting results have been reported on the ability of glandular-haired alfalfa (Medicago sativa L.) cultivars to reduce potato leafhopper, Empoasca fabae Harris, population abundance in field environments. We measured potato leafhopper adult and nymph abundance and yield responses in a cultivar selected for high potato leafhopper resistance ('54H91') and in a non-glandular-haired susceptible cultivar ('54V54') with and without insecticide treatment across 3 yr. Treatments included no insecticide and insecticide applied either early or late in each summer growth cycle. Date × cultivar × treatment interactions were found for potato leafhopper population abundance. In the absence of insecticides, total potato leafhopper abundance (adults + nymphs per sweep) was lower in 54H91 than in 54V54 on 85% of sampling dates; cultivar differences were especially evident as potato leafhopper abundance peaked. Insecticide treatment reduced potato leafhopper populations in both cultivars, but populations recovered and often exceeded the normal action threshold in both cultivars within 2-3 wk of insecticide application. Yield gain from early insecticide treatment of 54V54 was >400 kg/ha in 11 of 14 summer harvests, whereas in 54H91 the yield gain was <250 kg/ha in 10 of 14 summer harvests. We conclude that glandular-haired alfalfa cultivars with high levels of potato leafhopper resistance significantly suppress potato leafhopper adult and nymph abundance, reduce yield losses in the absence of insecticides, and have potential within an integrated pest management strategy to reduce insecticide use in alfalfa production systems.