Spread and Control of Biotype B Phylloxera
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.