Phytophthora blight (Phytophthora capsici): A serious threat to pepper and cucurbit production

Phytophthora blight, caused by oomycete Phytophthora capsici, is a serious threat to production of peppers and cucurbits worldwide. P. capsici can infect pepper plants at all growth stages, causing seedling death, root rot, crown rot, stem blight, and fruit rot. P. capsici can strike cucurbit plants at any stage of growth and causes seedling death, vine blight, leaf spot, and fruit rot. The infection usually appears first in low areas of the fields where the soil remains wet for longer periods of time. P. capsici is a soilborne pathogen and survives between crops as oospores in soil or mycelium in plant debris. An oospore is formed when mycelia of two opposite mating types (A1 and A2) grow together. Oospores germinate and produce sporangia and zoospores. Sporangia form when the soil is at field capacity and they release zoospores when soil is saturated. In Illinois, integrated approaches are used to manage P. capsici in peppers and cucurbits. Four approaches were evaluated for managing this disease in peppers, which included: (i) using resistant cultivars, (ii) induction of resistance in plants by red-light treatment, (iii) crop rotation, and (iv) fungicide application. In cucurbits, the disease is managed by: (i) seed treatment, (ii) crop rotation. (iii) removing or discing infected plants in low area, (iv) sanitation, and (v) fungicide application. At present, the following fungicides are used to manage Phytophthora blight of peppers and cucurbits in Illinois: chlorothalonil + oxathiapiprolin (Orondis Opti), cyazofamid (Ranman 400SC), ethaboxam (Elumin 4SC), fluopicolide (Presidio 4SC), mandipropamid (Revus 2.09SC), and mandipropamid + oxathiapiprolin (Orondis Ultra).