Minimizing Fertilizer Inputs for Variegated Leafhopper Management in Grapes

This research investigated the relationship between host plant (i.e,, grapevine) nitrogen status and population dynamics of the variegated leafhopper (VLH) in a commercia1 vineyard for three years. During each year, replicated fieli plots received the following treatments: 1) control (no fertilizer added), .’) 75 lbs. N / acre (synthetic ammonium nitrate), 3) 150 lbs. N / acre (synthetic ammonium nitrate), and 4) two tons of compost / acre ( = 38 lbs. N / acre). The response of VLH to these treatments was investigated by monitoring nymph densities and conducting oviposition (egg-laying) and nymphal development rate tests. During all three years, VLH nymph populations reached a seasonal peak during the first generation. Nymph densities during the second and third generations were especially low in 1989 and 1990, and reached a moderate level during the second generation of 1991. Oviposition tests conducted in July 1989 and June 1990 demonstrated greater VLH egg-laying in the synthetic fertilizer plots. However, oviposistion during the July 1991 test was greatest in the compost plots. No significant differences in VLH nymphal development rates were observed among treatments.