ASHS 2015 Annual Conference

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, and to understand which mechanism(s) are responsible for disease control. Data will be presented from a series of on-going field and greenhouse trials that test the effect of soil temperature, carbon source (e.g. rice bran, grape pomace, molasses) and cumulative anaerobic conditions (Eh in mVhr below 200mV) on suppression of Verticillium dahliae, Macrophomina phaseolina and Fusarium oxysporum. Results indicate that microsclerotia of V. dahliae can be reduced by 80% to 100% providing soil temperatures are above 18 °C and a cumulative Eh of 50,000mV hours below 200mV is achieved. Shifts in soil microbial communities and associated production of organic acid and volatiles during the anaerobic phase may be associated with disease suppression. Further, microbial shifts associated with ASD using rice bran (RB) as a carbon source persist for at least 10 months, and enhanced V. dahliae suppression was observed two years after ASD treatment despite multiple tillage operations and planting of rotation crops. 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. Trials are being repeated with refinements to see if greater pathogen control can be achieved. Additional carbon sources such as grape pomace and molasses are also being tested and impacts on nitrogen dynamics as well as production and disease incidence monitored. In 2014–15 1000ac of commercial strawberry and raspberries in CA were planted using ASD, and in one field demonstration organic strawberry yields were almost doubled using ASD relative to grower standard practices.