Spread and Control of Grape Phylloxera Biotype B

Objective 1: Variability in resistance of rootstocks to phylloxera In California’s viticultural regions we previously found two variants, biotypes A and B from own-rooted and AXR#1-rooted vines. This year we found 3 additional variants by searching on other rootstocks, St. George, Freedom and Dog Ridge. The new strains (named 1, 2 and 3) are less vigorous than the standard colonies of biotypes A and B on V. vinifera roots (Cabernet Sauvignon), but are able to form many galls on immature roots of some resistant rootstocks. Strains 1 and 2 grow poorly on AXR#1 as does biotype A, but strain 3, like biotype B, grows well on AXR#1. Based on our field and laboratory observations, these strains are not likely to kill resistant rootstocks but we are investigating whether they may be debilitating in the long-term. Analytical biochemical methods of M. A. Walker indicate that our biotypes A and B are genetically variable suggesting that biotype B may have arisen more than once, and that the capacity for biotype B arising anywhere is prevalent. If so, quarantines of biotypes are not useful and the potential for other strains to evolve is real. This work is continuing. Objective 2: Spread and hosts of biotype B Biotype B has been found in Napa, Sonoma, Lake, Alameda, Santa Clara, San Joaquin and Sacramento Counties, . The biochemical methods developed by M. A. Walker will enable us to track phylloxera variability more closely, but have not yet been able to distinguish Biotype A from B. We have observed phylloxera populations on alternative rootstocks at replant sites. Feeding is restricted to new roots and any reduction in vigor is apparently temporary. These observations are forcing us to reconsider the Phylloxera Task Force recommendation against interplanting. Objective 3: Alternative tactics to control phylloxera Besides our work with Enzone, we have evaluated (or will evaluate) Mocap (Rhone-Poulenc), imidacloprid (Bayer-Mobay), C02 and S02 (independent developer, Liquid Carbonic), four numbered experimental pesticides (Sumitomo Corp., Sankyo Co.). one numbered experimental compound (ISK Corp.), one experimental mixture of natural products (“Thunder,” Natural Earth Technologies, Inc.), one experimental material (Cidal Corp.) and an electronic method (HVT Corp.). We have decided not to evaluate other offered tactics because of limitations in resources and/or apparent lack of scientific basis. Enzone (Unocal) clearly kills phylloxera, however, the 1-2-year duration of the experiments has not enabled us to evaluate properly for ultimate improvements in vine health which we now know may not be seen within the first or second year of treatment. Our research provided some of the data necessan/ for the temporary registration of Enzone in Napa, Sonoma and Mendocino Counties. Our work with other therapeutic methods has not progressed to definitive field trials. In 3-4 year studies, we will determine population growth and damage on vines in large planter boxes to evaluate the potential of therapeutic methods in general. We are collaborating in a NASA and Mondavi funded project to evaluate remote sensing of phylloxera and development of geographic information system (GIS) to characterize phylloxera epidemiology.