The cucurbits are a diverse group of fruits and vegetables, including cucumber, squash, cantaloupe melon, watermelon, pumpkin and bitter gourd. These vining plants are especially useful in mixed cropping situations. They can be left to run over thesoil or be trained up poles and trellises, where they offer little competition to other crops in the stand. They are especially prone to a number of fungal and bacterial diseases, because of their large leaf area and big fruits, which are in contact withthe soil throughout their growth and development. The growth rate of cucurbits is extremely rapid. For instance, tropically grown cucumbers produce one new leaf per vine per day, which expands to 25 times its original size in about one week. With such phenomenal growth rates it is difficult to maintain fungicide deposits at the required levels without resorting to 4-5 day spray intervals. The following is an account of the major fungal and bacterial diseases of tropically grown cucurbits. Downy Mildew(fungus - Pseudoperonospora cubensis): This is a rainy season disease that thrives in the presence of free water and high humidity. Spore infection results in angular yellow spots that appear on the adaxial (upper) surface of the leaf. The correspondingarea on the abaxial (underside) of the leaf becomes covered with a grey fungal growth, which is the spore producing and bearing structures of the pathogen. The growth is more noticeable early in the morning, when heavy dew is present. Dissemination of spores and spread of infection is by wind, which accelerates during the cool temperatures, high humidity and dew of early morning. Downy mildew is essentially a wet season disease that may be controlled by the use of resistant varieties and a preventive fungicide spray programme, using copper-based products, chlorthalonil or mancozeb. Spraying should start at first flowering, and continue until the crop is harvested.
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