What Causes Pumpkin Leaves to Have White Patches?

Growing pumpkins in your home garden is a great way to get your family ready and excited for the fall; carving them up for Halloween, tasty pumpkin pies and roasting the leftover seeds are all part of a healthy crop. However, pumpkins are susceptible to damage from the environment. If you begin to notice white patches on the leaves of your pumpkin plants, they have contracted powdery mildew, and you must act before it ruins your fruit.

Powdery mildew is a fungal disease caused by the spores of the fungus Erysiphe cichoracearum. This disease can infect most plants, including pumpkins, cucumbers, melons and squash. The spores of this fungus are spread on the wind. This fungal disease will often appear in the middle or near the end of the growing season as the weather begins to get cooler and moister with the approaching autumn.

You'll first notice the disease as small white spots and patches on the leaves and stems of the plant, particularly on mature leaves. In severe cases, the disease can spread and turn entire leaves completely white, followed by yellowing, browning and withering. Eventually, infected leaves will die off and drop from the pumpkin plant. The white, powdery patches and spots will likely begin on older foliage but can quickly spread to newer leaves and kill them as well.

Powdery mildew will not spread to the pumpkin fruit itself; the only fruit that is directly affected by the disease is watermelon. However, the loss of leaves can cause serious damage to the plant and fruit. The pumpkins of infected plants will often be discolored and harden due to sunburn because all of the shading leaves have withered, died and fallen from the plant. This can result in stunted growth or fewer pumpkins while the plant itself tries to recover from the infection.

Your first step in controlling powdery mildew is to remove all infected foliage. This will help to slow or prevent the spread of the disease. Dispose of or burn the infected foliage away from other plants. There are a number of fungicides that will treat powdery mildew, including benomyl, chlorothalonil and dinocap. Spray all foliage as soon as you notice any signs of powdery mildew and continue to spray every seven to 10 days afterward, unless otherwise instructed by the product.