PM – Powdery Mildew
Scientific Name: Erysiphe betae
Type: Fungus
Powdery mildew is a fungal disease that affects the growth of beets, cantaloupes & melons, cucumbers, peas, squash, Swiss chard, and tomatoes. The fungal disease may cause poor growth of the fruits in cucumbers if the infection is severe. The leaves of the cucumber begin to wither and then fall off prematurely. The disease usually affects older leaves. The leaves tend to turn a light green or a yellow green when infected. A powdery white or light gray color mold appears on the underside of the leaves. An odor similar to that of a musty basement is noticeable in fields with severe powdery mildew. The disease can spread rapidly under favorable conditions and infect the entire leaves within a week. The disease is favorable with long periods of dry weather, warm days, and cool nights, and fluctuations of day/night temperatures. The most favorable temperatures are 54-81 F and usually occur in early spring and autumn when moisture and humidity are very high. The disease can spread rapidly and can infect a field within 5 days. Fungicides for powdery mildew can help manage the disease. Good air circulation and increasing space between the plants can help control and prevent the disease. The best option is to use disease resistant varieties.
WMV – Watermelon Mosaic Virus
Type: Virus - Potyvirus
Watermelon Mosaic Virus is a virus disease that affects the growth of cantaloupes & melons, cucumbers, gourds, pumpkins, squash, and watermelons. Watermelon mosaic virus is primarily a problem in the southern and western regions of the United States. Symptoms include stunted or dwarfed plants, yellow or light green mottling, blistering, marginal yellowing, leaf distortion, and reduced growth rate and yields. Losses of 50 percent or more in yield and fruit quality may occur. The fruit frequently show color breaking and warts. It is only spread by aphids. Symptoms usually begin to show in June. Plan on using a 3 year crop rotation and avoid planting in the same location, year after year. Plastic mulches have been shown to reduce losses. Insecticides for aphids are of limited value to control the disease. The best option is to use disease resistant varieties.