Watermelons are members of the cucurbit family of vine crops. Watermelons are a separate genus that does not cross-pollinate with other melons. Watermelons are a warm season crop that requires good sun and a well draining soil. When conditions change, the possibility of fungal infection in the crop is greater.
Wet soil that does not drain and low sun coverage are conditions that promote fungal infection in watermelon. Soil that is high in loam should be used when planting watermelon to promote good drainage. Shady plants in the area of your watermelon garden require trimming to allow more sunlight through. If soil in the area does not drain well, porous soil added to the mixture will improve drainage. Planting resistant varieties prevents infection by the most common fungi.
Symptoms of watermelon infection vary between kinds of fungi. Spots with white or tan centers, yellow areas on the leaf surface, spots which look like burning on the foliage and dead lesions are indications of fungal infection. Many fungal infections on watermelon plants are indicated by foliage issues.
Types of Infection
There are many varieties of watermelon infection, the most common varieties being foliar in nature. Cercospora leaf spot, downy mildew and gummy stem blight are the most common infections. These are indicated by a weakening of the stem, or the appearance of powdery mildews on the leaves of the plant.
Watermelon requires planting in disease-free soil where a previous infection has not occurred. Destroying watermelon plants that have been infected by burning keeps spores from spreading to other plants. Any plants in the area of the infection require culling. Planting of disease-free seeds and resistant cultivars in new soils will prevent infection.
Application of fungicide is determined by the watermelon disease and variety. Most diseases, such as scab, downy mildew and angular leaf spot can be controlled by fungicides, while fusarium wilt requires the destruction of the plant. If in doubt of the specific infection on your watermelon, contacting your local University Extension and sending tissue samples will help you determine the correct fungicide controls.