Grapevine deficit irrigation and its effect on mite (Acari: Tetranychidae) and leafhopper (Hemiptera: Cicadellidae) populations /by Emily Marie Smith.

Mites and leafhoppers are important pests of grapevines and can sometimes be hard to control. In this study, various levels of deficit irrigation were applied to Merlot grapevines during the summer to determine if mite and leafhopper populations could be manipulated by the amount of water applied to grapevines. There was a field and lab component to this project. In 2008, in Madera, CA, two treatments were used in the field component applying approximately 70 and 100% ET. In 2009, three treatments were applied at approximately 50, 70, and 100% ET to grapevines. No significant differences were seen in leaf water potential between treatments in year 1 except on 9/11/08 and only on 9/1/09 in year 2. Irrigation treatment goals were not achieved during the season and therefore, mite populations also showed no significant differences among treatments in either year 1 or 2. The lab component was held at UC Kearney Agricultural Center in a greenhouse using Pacific spider mites. Merlot vines were held at five different water stress levels (100, 80, 60, 40, and 20% ET) under two different temperature ranges to see how mite survival and reproduction was affected by water stress levels under different temperatures. No trends were seen in mite survival or reproduction across temperature or water treatments