Spread and Control of Biotype B Phylloxera
Summary From the 1990-1991 Report: Known biotype B sites are concentrated in the lower Napa and Alexander Valleys, with scattered sites elsewhere in Napa and Sonoma Counties only. Type B was detected on ungrafted Vitis vinifera and as a mixed population with biotype A for the first time. Laboratory tests of rootstock resistance detected no other biotypes and indicated that some resistant rootstocks are considerably less susceptible to grape phylloxera than others. Based upon these tests, own rooted \A vinifera vines and AXR#1, 41B and 0 43-43 rootstocks do not provide sufficient resistance to phylloxera, and some popular rootstocks are not as strongly resistant as others. In a release based on our research, the Phylloxera Task Force recommended sanitation, choosing the most resistant rootstocks and strategies for replanting to minimize the threat of grape phylloxera to vineyards. The efficacies on grape phylloxera of two organic phosphate compounds, carbon bisulfide and Electracat, an electronic device, were evaluated in the laboratory. All but the last were capable of killing grape phylloxera. A field test of the experimental pesticide Enzone in flood irrigation was discontinued because of inadequate control, but two tests of Enzone applications in drip irrigation are on-going. Collaborative research on rootstock breeding and physiological mechanisms of resistance were initiated. From the 1991-1992 Report: Biotype B grape phylloxera continues to spread in Napa and Sonoma Counties but is still unknown in other counties. According to results of a recent questionnaire, over 2000 acres of vineyards have been replanted in Napa and Sonoma Counties and another 6100 are currently infested with type B. No significant areas of Napa County are uninfested, whereas it has not yet been detected in some parts of Sonoma County. One Amador County and four Napa County rootstock field trials were examined for phylloxera. Phylloxera were only found in two of the Napa Valley trials. Samples from one of these trials contain a new strain. Bioassays of this strain indicate that it is much less vigorous than either type A or B on ^ vinifera roots, similar or slightly more vigorous than type A on AXR#1 roots, and more capable than both biotypes of feeding on callus and new roots of Freedom, Harmony, Dog Ridge, 1613 C and 5C. In these laboratory tests, the population did not grow rapidly on mature roots of any resistant rootstock tested. This strain (Strain 1) is not well adapted to any tested grape root as host and therefore is not yet considered a biotype akin to our A and B designations. It is not likely to kill any tested resistant rootstocks, however, more rootstocks must be tested. We plan experiments to determine whether it might economically stunt root growth of some resistant rootstocks. A collection from St. George led to a second strain (Strain 2) which has similar characteristics as Strain 1. We hope to determine the viticultural significance of these strains and continue the search for others. Roots of three accessions of Concord grapes were susceptible to biotype A and B. Winged phylloxera (alates) from a collection from Concord roots in Washington laid eggs that hatched and developed into sexual females, but alates reared from two California collections laid only non-viable eggs. This work confirms the existence of a viable sexual cycle for phylloxera in the Northwest, and the absence of this in California. Tests of chemicals to control phylloxera populations continue. Enzone trials indicate that phylloxera may be impacted but timing of multiple applications has not been worked out. A systemic insecticide candidate has been tested in the laboratory and kills phylloxera; whole plant tests are now warranted. Carbon dioxide and sulfur dioxide were tested in the laboratory; carbon dioxide takes too high a concentration and too long to kill and does not appear to be a good possibility for use in control programs. Sulfur dioxide kills phylloxera at a concentration of 10%in nitrogen for as short as 5 minute exposure. Further testing on potted plants and a vineyard is planned.