Well, it's that time of year when we start getting lots of calls and questions about common garden diseases and pests. This post will be the first in a series focusing on how to manage these issues when they arise so that they don't get out of hand. It is wise to pay careful attention to your plants - sometimes small changes in their appearance can indicate a potential problem. The internet is a wonderful resource for solving your garden mysteries, but a good gardening book like Rodale's is indispensable for the serious gardener. If neither resource is available to you, don't hesitate to call us and we can help you troubleshoot! What is Powdery Mildew (PM)?
Powdery mildew is a white fungus that mainly affects plants in the squash family (cucumbers, melons, zucchinis, etc.) but can also affect other families as well. It first appears on the undersides of leaves as white dots, which expand until the whole leaf looks like it's been dusted with a white powder.
What causes PM?
Garden fungi are propagated by spores that fly on the air, which makes them difficult to prevent. The fungi are more likely to grow on plants with a lot of moisture in and on their leaves, and in humid conditions with too little air circulation. It is also carried from plant to plant by insect pests such as squash bugs, cucumber beetles, aphids, and flea beetles, so managing these pests helps reduce the prevalence of PM.
How do I prevent PM?
- Check for insect pests every few days. Squish the pests when you find them, and make sure to look for and destroy their eggs as well. A little vigilance goes a long way!
- Space plants further apart so that the sun can hit all parts of the plant, and air can move easily through.
- Only water in the morning, when plants will have plenty of time to dry during the day.
- Practice good crop rotation. Never put plants in the squash family in the same place as they were the year before.
How do I manage PM once I have it?
Powdery mildew does not usually kill a plant unless it is also suffering from pests. However, the two often go hand in hand, so it is wise to manage it when you see it. Here's what to do:
- Remove the worst-infected leaves with a pair of scissors or pruners. DO NOT put the infected leaves in your compost pile! Either burn them or put them in the trash. After pruning, wash your hands and tools with soapy water or a dilute bleach solution before touching other plants.
- Spraying with a sulfur- or copper-based fungicide once a week on the top and undersides of the leaves will eliminate most of the fungus. Follow this regimen up until 2 weeks before harvest. Alternatively, a mixture of 1 teaspoon of baking soda per quart of water can also be used. Try to spray only in the morning, when the leaves will have plenty of time to dry in the sun.
