Fungus on Squash Leaves

Powdery Mildew

• There are numerous species of fungal spores that cause powdery mildew. Erysiphe cichoracearum is the species that attack squash plants, according to North Dakota State University. Fungal spores are able to spread to plants through the wind. Despite the fact that powdery mildew germinates during humid weather conditions, this disease is at its worst during dry weather, according to Colorado State University. Other environmental and cultural factors that favor powdery mildew include saturated soil, squash plants planted too close together and shade.

Symptoms

• Squash plants infected with powdery mildew display a white talcum looking powdery growth on leaves, according to Colorado State University. Generally, older leaves contract powdery mildew in mid to late season, according to North Dakota State University. When powder mildew is allowed to run rampant, it causes leaves to turn yellow and wither. Squash is unaffected by the disease; however, plants may not produce a bountiful crop due to loss of vigor. Treating your powdery mildew is important to prevent your squash plant's health decline.

Chemical Control

• Prune off damaged leaves from your squash plant, as recommended by Colorado State University. Apply a fungicide that contains an active ingredient such as benomyl, chlorothalonil, or dinocap, as suggested by North Dakota State University. It is important for gardeners to apply a fungicide as soon as symptoms occur. Monitor your squash plants throughout the growing season, especially during humid weather conditions. Reapply the fungicide according to its directions. Water your plants to prevent causing harm with the fungicide.

Cultural Control

• Reduce the humidity around your squash plants by watering them at their base, as suggested by Colorado State University. You can also use a drip irrigation system. Remove all diseased debris underneath your squash plants. Throw away or burn up the diseased debris. Throwing the debris in your compost results in spreading the fungal spores over the rest of the garden. Prevent future powdery mildew problems by spacing squash hills 48 inches apart, as recommended by the University of Illinois.