Fungicide management of Phytophthora capsici in bell pepper

Phytophthora blight, caused by Phytophthora capsici, is a destructive disease of peppers and cucurbits in Illinois and worldwide. Fungicide use is a significant component of management strategies of Phytophthora blight of peppers. Studies were conducted in the laboratory and field to evaluate efficacy of selected fungicides for management of Phytophthora blight of peppers in Illinois. In the laboratory, sensitivity of five P. capsici isolates from Illinois was evaluated to the fungicides cyazofamid, dimethomorph, mandipropamid, and oxathiapiprolin. Development of colonies and production of sporangia of the isolates were assessed at concentrations of 0.0, 0.1, 0.5, 1.0, 5.0, and 10.0 µg mL-1 of cyazofamid; 0.0, 0.1, 0.5, 1.0, 2.5, and 5.0 µg mL-1 of dimethomorph; 0.0, 0.05, 0.1, 0.5, 1.0, and 5.0 µg mL-1 of mandipropamid; and 0, 1, 10, 50, 100, and 200 µg mL-1 of oxathiapiprolin in V8 juice agar in Petri plates. Mycelial growth and sporangia production were significantly (P=0.05) reduced by all four fungicides tested in the laboratory. The EC50 values of the fungicides for mycelial growth ranged from 0.34 to 3.63 µg mL^-1 (average 1.03 µg mL^-1); from 0.75 to 4.66 µg mL^-1 (average 2.98 µg mL^-1); from 0.13 to 7.18 µg mL^-1 (average 4.03 µg mL^-1); and from 0.03 to 0.97 µg mL^-1 (average 0.28 µg mL^-1) for cyazofamid, dimethomorph, mandipropamid, and oxathiapiprolin, respectively. The EC50 value for sporangia production was 10, 2.5, 0.05, and 100 µg mL-1 for cyazofamid, dimethomorph, mandipropamid, and oxathiapiprolin, respectively. In 2016, effectiveness of fungicides cyazofamid (Ranman 400SC), mandipropamid (Revus 2.09SC), cymoxanil + famoxadone (Tanos 50WDG), and oxathiapiprolin (Orondis Opti-A) for management of P. capsici in bell pepper in the field was investigated. Percent asymptomatic plants in the plots drenched with Ranman 400SC or Orondis Opti-A at transplanting were significantly higher than those of the plots either were sprayed with Ranman 400SC + copper (Kocide-3000 41.6Df) or drip-delivered Orondis Opti-A at transplanting.