What Can You Put on Pumpkin Vines for Mildew Without Harming Bees?

Powdery Mildew

• The type of powdery mildew that infects pumpkin vines is caused by two different fungal spores: Erysiphe cichoracearum and Sphaerotheca fuliginea. These spores require high humidity to germinate, but do not need wet weather conditions to spread. Gardeners must monitor their pumpkin plants when temperatures are between 68 to 81 degrees Fahrenheit or when temperatures favor fungal spore germination. This disease is spread through the wind. Pumpkins planted too close together are at risk for contracting powdery mildew.

Symptoms

• Powdery mildew produces a white fungal growth on vines, foliage and stems. Severely infected leaves shrivel, turn yellow and defoliate off of the vine. Loss of foliage prevents proper photosynthesis. In addition, pumpkins become sun burnt on defoliated plants. The result is deformed pumpkins and a reduction in yield. Because powdery mildew may occur when your pumpkins are blooming flowers, it is important to use a fungicide that will not kill off bees and prevent pollination.

Chlorothalonil

• Chlorothalonil is safe to use around bees, according to Purdue University. This organochlorine fungicide must be used as soon as your notice powdery mildew's symptoms for the product to work. Spray pumpkin vines every 7 to 10 days with chlorothalonil. Increase the effectiveness of the fungicide by removing any infected plant debris around the plant. Rake up the debris and burn or throw away. Avoid placing the debris in your compost to prevent spreading the fungal spores over the yard.

Azoxystrobin

• Azoxystrobin is a non-hazardous fungicide to bees, according to Clemson University. This methoxyacrylate compound stops the growth of powdery mildew. Furthermore, azoxystrobin is in the same chemical family as strobilurins, which is a compound found in mushrooms. When spraying azoxystrobin, continually agitate the substance to keep the product effective. Wear safety gear such as long sleeves and a mask. Avoid spraying right before a rainfall or on a windy day. Reapply according to the directions.