ALTERNATIVES TO METHYL BROMIDE FOR ROOT DISEASE MANAGEMENT
Department of Plant Pathology, University of California, Davis, CA 95616, USA
Background and objectives
Results and conclusions
Fumigation with mixtures of methyl bromide (or some chemical alternative) and chloropicrin effectively controls V. dahliae, Phytophthora species, and most other major pathogens of known importance in soil. However, soil fumigation can nearly double strawberry yields even when known pathogens are not present, and we are researching mechanisms of this general yield response to fumigation. Relative to non-fumigated soils, total numbers of fungi are usually low for several months following fumigation, while total numbers of bacteria remain high with a heavy representation of Pseudomonas species. These differences in soil populations also occur, with some modifications, in the rhizosphere of growing strawberries. We are currently testing the effects of rhizosphere and root-associated microbes from fumigated and non-fumigated soils on the growth and root health of strawberries.
A variety of non-chemical alternatives to soil fumigation with methyl bromide have been tried. Crop rotation, in comparison to continuous strawberry, can be beneficial. For example, 1-year rotations with rye or broccoli increased subsequent strawberry yields 18-24% at one location, but had no beneficial effect at a second location. Furthermore, these 1-year rotations did not reduce Verticillium wilt significantly. Soil solarization has limited prospects because of a foggy coastal climate at the time treatment is feasible. Various organic amendments and approaches have been tried by others, but results are variable and none gives a consistent yield response approaching that obtained by soil fumigation. Although additional non-chemical approaches need to be tried, it is unlikely that non-chemical methods of soil treatment can fully duplicate the level of pathogen control and yield enhancement obtained with pre-plant fumigation. Furthermore, the use of effective soil fumigants for the production of quality runner plants in nurseries will remain critical to profitable strawberry production, regardless of the type of management approach finally used in berry production fields.