Effect of Drive Row Ground Covers on Hop (Rosales: Cannabaceae) Yard Arthropod Pests in Vermont, USA

Alternatives to pesticides are necessary for the management of hop (Humulus lupulus L.) arthropod pests. The three major arthropod pests in northeastern US hop production include two-spotted spider mite, Tetranychus urticae Koch, hop aphid Phorodon humuli (Schrank), and potato leafhopper, Empoasca fabae Harris. This 3-yr study (2012-2014) in Vermont investigated the effect of flowering ground covers on arthropod pest abundance. Hop cultivars 'Nugget' and 'Cascade' were evaluated under a strip-split plot experimental design. Ground cover treatments included 1) Control: mowed red clover (Trifolium pratense) and resident weeds, 2) Clover: red clover, and 3) Diverse: common yarrow (Achillea millefolium), beebalm (Monarda fistulosa), red clover, and annual sunflower (Helianthus annuus). Natural enemies were grouped by associated pest and indicated by our mixed model to be strong predictors of the number of hop aphid and potato leafhopper on hop plants. In year two, ground cover treatment had a significant effect on two-spotted spider mite abundance where fewer two-spotted spider mite were observed on hop plants in Diverse plots. The established, un-mowed Clover treatment was preferred by potato leafhopper over Diverse ground cover and hop plants. This revealed the potential for clover ground cover to serve as a trap crop for potato leafhopper management in northeastern hop yards. Our findings are evidence that ground covers implemented for conservation biological control may serve more specific pest management functions instead of or in addition to boosting top-down pest pressure.