Effect of sudangrass biosolarization on Verticillium dahliae populations in coastal California

A field experiment was conducted at an organic field in the central coast of California (USA) to test the effects of soil solarization and sudangrass residues on Verticillium dahliae populations, plant health, and yields in organic strawberry (Fragaria × ananassa Duch.) production. Using a split plot design, a crop of sudangrass (Sorghum × drummondi (Nees ex. Steud.) Millsp. & Chase) was mowed and then split into two treatments: surface mulch or incorporated into the soil. The sudangrass treatments and a control were tested with or without soil solarization. Maximum soil temperatures recorded in solarized plots were 53 and 42°C at soil depth of 5 and 15 cm depth, respectively. Solarization significantly reduced V. dahlia populations (p=0.01) and disease incidence (p<0.01), and increased yields (p<0.01) over non-solarized plots. Sudangrass treatments did not affect V. dahlia populations (p=0.33) or yields (p=0.25). However, mulched plots had lower plant mortality (p<0.01) than other sudangrass treatments (p=0.03). Results indicate that solarization can be used in coastal Mediterranean environments production to reduce disease V. dahliae incidence and increase yields.