Long Island Cheese Pumpkin growing

Asked August 8, 2019, 8:20 PM EDT

hi there! Two questions actually-- I have a little powdery mildew on my pumpkin vine leaves and my squash leaves-- I removed the leaves that had a lot. Will it kill my plant? What can I do? Also, my pumpkin vine has three lovely pumpkins. This week, it set another fruit and it seems to be growing (as opposed to yellowing and falling off...) Should I remove the fruit so as to let the nutrients go to the existing fruit, or let it grow? Thank you! Emily

Multnomah County Oregon pumpkins powdery mildew powdery mildew on cucurbits

1 Response

Hi Emily,

When weather conditions are favorable, powdery mildew often develops on a wide range of plants. High humidity promotes disease development, making it a common disease in the Midwest this time of year, especially when cool, damp evenings follow warm days. These fungi are unusual compared to most plant disease fungi because they do not cause infection when the leaves are wet; they just require high humidity during infection. However, they produce more spores when the humidity is low.

Young growth is most susceptible on most plants. The fungus can grow on all above ground parts of plants, including both sides of the leaves, stems, flowers, and fruit. Many powdery mildew fungi only grow on the top side of the leaf, but some will grow on both sides. Fungal growth may completely cover the leaf, or may appear only in patches. Severely infected foliage may be yellow, distorted or stunted. Disease can spread rapidly (3 days) when conditions are optimal, but it usually takes 7-10 days from infection until symptoms develop and secondary spore production occurs. Fortunately, powdery mildew is only a cosmetic problem on most plants. It will make the plant look a little ragged, but it doesn’t kill the plant.

Cultural controls will help minimize problems with powdery mildew:

  • Select powdery mildew-resistant varieties when available. This won’t completely eliminate the disease, but it will help disease severity.
  • Reduce humidity around the plants. Obviously you can’t change the weather, but you can change the microhabitat around your plants. Increase the spacing between plants to increase air flow. Place plants where they will receive morning sunshine and dry out more quickly, if possible. And don’t overwater.
  • Avoid over fertilizing, since high nitrogen promotes tender leaf formation, and promotes dense stands that are more likely to become infected.
  • Remove and destroy severely infected plants, if possible.
  • Clean up infected plant debris in the fall to reduce overwintering fungal structures that will produce spores during the next growing season.

In some cases, for some plants, however, powdery mildew can cause severe leaf loss and yield reduction in vegetables. In this case fungicide applications may be necessary to reduce or prevent injury. A number of fungicides are registered for use against powdery mildew. Regardless of which type you select, be sure to READ THE LABEL and FOLLOW THE INSTRUCTIONS to make sure you use the fungicide in the most effective manner possible. Note that not all products are registered for use on vegetable crops, and sulfur can be damaging to some squash and melon varieties. Begin treatment on valuable plants when symptoms appear to prevent the disease from spreading.

An alternative to commercial fungicides is to spray approximately once a week with a solution of baking soda (1.5 tablespoon/gallon) and horticultural oil (3 tablespoons/gallon).

As to your new pumpkin since it takes 70 to 110 days to maturity I recommend removing the new fruit and focusing on the older pumpkins. However, ultimately it is your decision whether or not you think it has enough time to mature.

Good luck and happy gardening.