Anaerobic Soil Disinfestation, Not Wheat Pre-cropping, Suppressed Charcoal Rot in Strawberries

Charcoal rot caused by <i>Macrophomina phaseolina</i> (<i>Mp</i>) has become a major threat to the California strawberry industry. We examined the effect of growing 'Summit 515' wheat (wheat) as a pre-crop of strawberries with and without anaerobic soil disinfestation (ASD) on suppressing charcoal rot in strawberries. A series of pot experiments, replicated field trials on the Central Coast, and demonstration trials on commercial fields in the Southern Coast were conducted. Economic analysis using a partial budget was performed using data from the field trials. Growing wheat did not significantly reduce soil <i>Mp</i> populations, and growing and incorporating wheat failed to suppress charcoal rot in strawberries in a replicated field trial. In contrast, ASD applied within beds (bed-ASD) in a sandy loam demonstration trial and ASD applied on a flat ground (broadcast-ASD) in loamy sand replicated field trials suppressed charcoal rot in strawberries. However, the <i>Mp</i> populations in the soil were significantly reduced only in the demonstration trial. Potential mechanisms and cumulative Eh and cumulative soil temperature conditions required for those cases are discussed. In a clay loam demonstration trial, bed-ASD did not develop sufficient anaerobiosis and failed to suppress the disease because of large soil clods in the beds. A partial budget economic analysis indicated that broadcast-ASD may be cost-prohibitive, whereas the bed-ASD is more viable. Taken together, bed-ASD may be a viable option for suppressing charcoal rot in strawberries in sandy to loamy fields in the Southern Coast of California. Bed-ASD in fields with high clay content soils remains challenging.