2019 ASHS Annual Conference

The effects of soil solarization and sudangrass (Sorghum X drumondii (Nees ex Steud.) Millsp. & Chase) cover crop treatments were tested on weed and Verticilium dahliae (Kleb.) populations on the Cal Poly Organic Farm, San Luis Obispo, CA. Sudangrass was grown, mowed and then developed into two treatments: surface mulch (CCM) or incorporated (CCI) into the soil. The sudangrass treatments and a control (NO CC) were tested with and without soil solarization (n=4). Maximum soil temperatures in solarized plots were 48°C at a soil depth of 5 cm and 42°C at a soil depth of 15 cm. On average, temperatures in CCM plots were 2-3°C lower than other solarized plots. Temperatures in all solarized plots were 10-15°C higher than non-solarized plots. In initial weed biomass assessments, taken 6 weeks after tarp removal, non-solarized CCI plots reduced weed biomass by 24.4% compared to the control (p=0.30). Non-solarized CCM plots reduced weed biomass by 95.6% compared to the control (p=0.002). All solarized plots resulted in similar reduction in weed biomass compared to the control with an average reduction of 97.1% ± 0.6% (p=0.001). Efficacy of solarization treatments decreased with time. In final weed biomass assessments, taken 15 weeks after tarp removal, the only solarization treatment providing a significant reduction in weed biomass compared to the control was CCI with solarization (p=0.047), resulting in 67% lower biomass than the control. CCM plots without solarization also provided significant control (p=0.016), reducing weed biomass to 84.1% of the control. Solarized CCI and solarized NO CC plots both reduced V. dahliae levels to 1.5 CFU/g compared to baseline levels of 13 CFU/g (CCI, p=<0.001) and 8 CFU/g (No CC, p=0.037). V. dahliae populations were unaffected in other treatments. Results indicate that soil solarization can help manage annual weed and V. dahliae populations in organic strawberry production. Sudangrass residues can reduce weed populations but have limited effect on V. dahliae populations unless combined with soil solarization.