|Authors: ||C. Shennan, J. Muramoto, G. Baird, M. Zavatta, L. Toyama, M. Mazzola, S.T. Koike|
|Keywords: ||soilborne diseases, crop rotation, soil biology|
Anaerobic soil disinfestation (ASD), a biological alternative to soil fumigation, has been shown to control a range of soil-borne pathogens and nematodes in numerous crop production systems.
Current work is focusing on how to optimize ASD (in terms of carbon source used, temperature and degree of anaerobiosis attained) to control specific sets of pathogens for California strawberries.
A series of on-going field and greenhouse trials are testing the effect of soil temperature, carbon source (e.g., rice bran, grape pomace, molasses) and cumulative anaerobic conditions (Eh in mV h below 200 mV) on suppression of Verticillium dahliae, Macrophomina phaseolina and Fusarium oxysporum. Earlier work found that numbers of viable microsclerotia of V. dahliae in soil can be reduced with ASD using rice bran as a carbon source by 80 to 100% providing soil temperatures are above 18°C and a cumulative Eh of 50,000 mV h below 200 mV is achieved.
Yields equivalent to those achieved with soil fumigants can be obtained, and use of ASD with rice bran (RB) eliminates the need for pre-plant fertilizer in strawberry systems.
Shifts in soil microbial communities and associated production of organic acid and volatiles during the anaerobic phase may all be associated with disease suppression.
In an organic field trial, we observed that ASD not only reduced V. dahlia severity in strawberry plants, but also resulted in lower numbers of microscleotia in the soil almost two years after treatment following an untreated lettuce crop.
Temperature and Eh thresholds for other pathogens are being determined.
When soil temperatures are high, ASD with RB as a carbon source shows promise for reducing Fusarium and Macrophomina, but did not provide complete control in field trials.
Trials are being repeated with refinements to see if greater pathogen control can be achieved.
In 2014-15, 400 ha of commercial strawberry and raspberries in California were planted using ASD, and in one field demonstration organic strawberry yields were doubled using ASD relative to grower standard practices.
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