Control of Phytophthora root and crown rot of bell pepper with composts and soil amendments in the greenhouse

Ten composts and soil amendments were evaluated in the greenhouse for control of Phytophthora root and crown rot of bell pepper caused by Phytophthora capsici. Three rates of calcium humate, calcium sulfate, chitosan, citrus pulp, citrus pulp with molasses, crab shell waste, humate, mustard residue, composted sewage sludge-yard trimming, and wood chips were incorporated into soil in pots prior to transplanting 6-week-old bell pepper cultivar Early Calwonder. P. capsici zoospores (2 × 10⁴) were placed into the soil of each pot 2 weeks after transplanting. Areas under the disease progress curves (AUDPC) for disease severity and stem lesion length were determined, and final root and shoot dry weights were also evaluated. Soil populations of five microbial functional groups, and total microbial activity, measured by fluorescein diacetate hydrolysis analysis, were evaluated. Certain rates of chitosan, crab shell waste, and citrus pulp with molasses significantly reduced disease severity and/or stem lesion length, and increased root or shoot dry weights, compared with unamended controls. None of the other treatments were effective in reducing root and crown rot of bell pepper. Citrus pulp with molasses was unique in enhancing the total microbial activity and populations of certain microbial functional groups, compared with unamended controls.