Phylloxera variability: Four “non-A, non-B” strains from various resistant rootstocks survive on some rootstocks that are resistant to types A and B. In laboratory tests, one strain increased 15-fold on Harmony rootstock suggesting the potential for damage in the field. Field observations at the original collection site will evaluate the susceptibility of Harmony to this strain. The other strains grow slowly on resistant rootstocks in the laboratory. They appear incapable of damaging mature resistant rootstocks, but their effect on new plantings needs further evaluation. We assisted M. A. Walker with electrophoretic and DNA characterization of some of our laboratory colonies. His data indicate more variability than expected and suggest the need for better understanding of life cycles, biology, and worldwide variability in phylloxera. Characterization of variability is critical for testing breeding materials in Walker’s rootstock program. Additional DNA testing will begin in June. Potential for control other than with rootstocks: We evaluated several products in the laboratory. The toxicity of some insecticides justifies further testing. Several non-conventional products including microbes, plant extracts, nutritional supplements and surfactants appear to be incapable of killing phylloxera in the field and unable to protect plants by enhancing the natural defenses and vigor of vines. Continued screening of such products is necessary to detect any that has merit and to provide growers and farm advisors with scientific information on products they might encounter on the market. We found that infested vines grown in low fungi environments were less damaged than untreated infested plants grown. This suggests that fungi cause some and possibly much of the damage to vines. If so, insecticides might not cure damage because the secondary fungal infections could persist after phylloxera are eliminated. We began new greenhouse tests to evaluate several insecticides and determine which fungi cause damage. We are setting up a Sonoma Co. trial to test whether insecticides can slow spread of damage. Other field trials to investigate whether fungicides can be curatives awaits the new funding cycle. Factors that affect the spread of damage: Research with scientists at NASA, Robert Mondavi Winery and Chico State University is investigating whether remote sensing can detect phylloxera infestations. The initial analyses are cause for optimism. The method will be critical for understanding the highly variable rates of spread of phylloxera populations and damage. Remote sensing is potentially feasible commercially. The plots for the 1994 field season have been set up.
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.
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.