Date of Award

6-2011

Degree Name

MS in Agriculture - Plant Protection Science

Department

Horticulture and Crop Science

Advisor

Michael Costello

Abstract

Western grape leafhopper (WGLH) (Erythroneura elegantula Osborn) is a serious pest of grape (Vitis vinifera L.) in many commercial vineyard growing regions of California. WGLH injures vines by removing leaf photosynthetically active area, resulting in the reduction of leaf efficiency, ultimately reducing yield and fruit quality. Regulated deficit irrigation (RDI) is a widely adopted irrigation strategy that reduces irrigation during critical phenological growing points (i.e., berry-set to verasion) to manage vegetative growth and berry size of red varieties. Leafhoppers are known to respond negatively to vine water stress. In a two year study at a commercial vineyard located in Paso Robles, California, RDI was imposed on Cabernet Sauvignon winegrapes. Two treatments were looked at, intensity of deficit (25% and 50% of the grower’s standard irrigations, i.e., close to 1.0 ETc) and, duration of deficit (3 weeks and 6 weeks, starting at berry set). Weekly counts of WGLH nymphs were taken, and then eggs were counted after the end of the second and third generations. Vine water status was monitored with a pressure chamber and stomatal conductance was measured with an LI-6200 CO2 porometer. Results confirm other studies that have shown that leafhoppers are sensitive to vine water status. In year two of the study, second generation WGLH nymphal density was significantly reduced by RDI but the effect did not last through the third generation, and there was no difference in intensity or duration of the deficit. Second generation WGLH oviposition was also significantly reduced by RDI, and there was no difference in intensity or duration of the deficit. However, oviposition was reduced in the third generation only in the 25% deficit treatment, and there was no difference between deficit duration. One possible explanation for lower oviposition is leaf epidermal tissue becomes more difficult to penetrate due to a physiological response to thicken leaf cuticle in an attempt to conserve water during times of water stress. This reduction in egg density may in part, explain the reduction in nymphal density.

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