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Significance

Phytophthora blight has become one of the most serious threats to production of cucurbits and peppers worldwide. Phytophthora capsici on cucurbits was first reported in 1937 in California and Colorado. Since then, Phytophthora blight has been observed in cucurbits and peppers in most of the vegetable producing areas in the world. Phytophthora capsici commonly occurs in temperate, subtropical, and tropical environments.

Recently, the incidence of Phytophthora blight on cucurbits has dramatically increased in Illinois and other cucurbit growing areas in the world, causing up to 100% yield loss. The cucurbit industries, particularly processors, have been seriously threatened by heavy crop losses due to Phytophthora blight. For example, outbreaks of Phytophthora blight have threatened the pumpkin processing industry in Illinois, where approximately 90% of the US processed pumpkins are grown (Figure 17). Similarly, the pickling cucumber industry of Michigan also has been jeopardized due to Phytophthora blight. In addition to the food industry, cucurbits are grown for educational, recreational, and social purposes (Figure 18). Because of heavy crop losses due to Phytophthora blight, some growers have had to abandon their farms and move to different areas to find noninfested fields.

Figure 17.

Figure 18.

Because P. capsici has a wide host range, it is difficult to control Phytophthora blight. More than 50 plant species, including several weed species, in more than 15 families are hosts for P. capsici. Among the major hosts of P. capsici are red and green peppers (Capsicum annuum), watermelon (Citrullum lanatus), cantaloupe (Cucumis melo), honeydew melon (C. melo), cucumber (Cucumis sativus), blue Hubbard squash (Cucurbita maxima), acorn squash (Cucurbita moschata), gourd (C. moschata), processing pumpkin (C. moschata), yellow squash (Cucurbita pepo), zucchini squash (C. pepo), tomato (Lycopersicon esculentum), black pepper (Piper nigrum), and eggplant (Solanum melongena).

Currently, there is no single control method that is adequate to provide control of P. capsici on cucurbits. There are no cucurbit cultivars with measurable resistance to this disease. Crop rotations are virtually ineffective in controlling P. capsici because the pathogen can survive for several years in the soil, and it can infect more than 50 plant species. Outbreaks of the disease are seriously threatening the production of cucurbit crops (Figure 19). Additional research is needed to develop effective strategies for the management of Phytophthora blight on cucurbits and other vegetables.

Figure 19.