Comparison of foliar and soil formulations of neonicotinoid insecticides for control of potato leafhopper, Empoasca fabae (Homoptera: Cicadellidae), in wine grapes.

BACKGROUND The potential of systemic neonicotinoid insecticides to control potato leafhopper, Empoasca fabae (Harris), a damaging pest of wine grapes in the eastern United States, was investigated. Soil or foliar applications were made to potted or field-grown vines, and the response of leafhoppers was determined in clip cages over the following month on young or mature leaves. RESULTS Foliar application of imidacloprid caused immediate and long-lasting reductions in E. fabae survival on both leaf ages, whereas the activity of soil-applied imidacloprid was delayed. Clothianidin, imidacloprid and thiamethoxam all provided long-lasting reduction in leafhopper survival on young and mature foliage when applied through either delivery route. However, the percentage of moribund nymphs was significantly greater on foliar-treated vines and increased over time in mature and immature leaves compared with soil-treated vines. Residue analysis of foliar-applied imidacloprid showed an 89% decline in mature leaves from day 1 to day 27, and a 98% decline in immature leaves over the same time period. Comparison of soil-applied clothianidin, imidacloprid and thiamethoxam in field-grown vines showed significant reduction in E. fabae only on mature leaves of vines treated with thiamethoxam. CONCLUSIONS Neonicotinoids can control E. fabae in small vines, even in rapidly expanding foliage where this pest causes greatest injury. Soil application provides superior long-term vine protection because declining residues on foliar-treated vines lead to suboptimal activity within 2-3 weeks. Vineyard managers of susceptible cultivars may take advantage of this approach to E. fabae management by using foliar applications of the three neonicotinoids tested here, or by using soil-applied thiamethoxam.