UC research identifies new emerging soilborne diseases of strawberry

The Issue

With the impending loss of the methyl bromide fumigant for use in combating soilborne diseases, researchers anticipated that new challenges would eventually emerge and affect strawberry production in California. Such new challenges have indeed developed. Beginning in 2007, growers who no longer used methyl bromide began to see weak spots in their fields where strawberries did not grow vigorously, produced fewer fruit, and eventually collapsed and died. These problematic areas increased in size in subsequent years. In some locations, a large percentage of the strawberry plants performed poorly and died prematurely. Such plant losses could have significant effects on this industry, which produces approximately 80 percent of the nation’s strawberry crop.

What Has ANR Done?

A UC research team consisting of county-based farm advisors (Steven Koike, Oleg Daugovish, Mark Bolda) and campus-based researchers (Tom Gordon, Husein Ajwa, Krishna Subbarao) initiated a multi-year investigation of the problem with funding from the California strawberry industry. The UC team discovered that the strawberry problem was caused by two distinct soilborne pathogens, Macrophomina phaseolina and Fusarium oxysporum. It now appears that the previous practice of using methyl bromide + chloropicrin soil fumigation was able to suppress the development of such new problems; with changes in soil fumigation practices, these pathogens were able to become established and cause crop loss. Prior to their study, neither fungus was known to occur on strawberries in California, making their report the first record of these strawberry diseases in the state. Further investigations documented that these new pathogens are present in three major strawberry production areas in California, that alternative chemical soil treatments provide some but not complete control, and that a few strawberry cultivars are apparently resistant to the new pathogens. Management options for growers have been presented to the industry at extension field events. Additional research is planned to further study the biology of the pathogens and to develop additional resistant strawberry cultivars.

The Payoff

Strawberry industry put on alert regarding emerging threats.

This UC research team was able to identify the nature of the strawberry collapse problem occurring in various counties in California. Growers now are aware of these emerging pathogens and can take steps, such as the cleaning of farm equipment, to limit the spread of infested soil into clean fields. Researchers and growers are collaborating to seek out ways to manage the two diseases. UC breeders are initiating research to develop resistant strawberry cultivars. UC research and extension programs, therefore, are actively working to protect this $2.3 billion industry.

Contact

Supporting Unit:

Monterey, Ventura, and Santa Cruz counties, UC ANR Cooperative Extension; and UC Davis Departments of Plant Pathology and Plant Sciences.
 
Steven T. Koike, (831) 759-7350, stkoike@ucdavis.edu