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Powdery Mildew on Cucumbers

powdery mildew Picture
Powdery Mildew on Cucumbers

What does powdery mildew on cucumber plants look like?

Powdery mildew strikes with little warning, leaving your cucumber and squash foliage looking like it has been sprinkled with baby powder. Initially, powdery mildew affects a few leaves and may go unnoticed, but as the fungus (Podosphaera xanthii) spreads, entire plants may be affected. Although powdery mildew does not directly affect the fruit, infected foliage yellows, turns brown and eventually dies, leaving cucumbers and squash exposed to the sun. 

When the entire cucumber bed is infected, this may mean significant leaf drop, compromising the plant's ability to make and store food. The resulting fruit is inhibited, lacks characteristic flavor and may wither on the vine.

What causes powdery mildew on cucumbers and squash?

Powery mildew is a fungal infection caused by the Podosphaera xanthii fungus. There are several conditions that increase the chances of your cucumber (and squash) plants becoming infected with powdery mildew.
  • Warm Humid Weather
  • Poor Air Circulation
  • ​Low Light
  • Overcrowded Plants
Powdery mildew typically strikes when weather is warm and the relative humidity is high. According to the Cornell University Extension Services, the organisms responsible for powdery mildew thrive in dry soil and often appear first on lower leaves or leaves that receive low light.
Overcrowded plants contribute to the problem, as air circulation and sunlight is inhibited, creating a breeding ground for powdery mildew. This year, I planted cucumbers and summer squash in raised beds and was delighted by their lush growth early in the season, but as warm weather approached and the humidity levels soared, these plants developed powdery mildew. Those I planted 200 yards away in a garden plot show no signs of powdery mildew. In this case, I definitely think that being overcrowded was the major contributing factor to the appearance of powdery mildew.

How do you treat plants with powdery mildew?

Fungicides are an effective means to control powdery mildew, but pose a problem if your plants are in the production stage, as the fungicides are not safe for human consumption. Treating plants with fungicides may control the spread of powdery mildew, but you won't be able to eat your cucumbers and squash. For best results, treat plants with fungicides before plants set fruit or symptoms appear.

For plants that already show signs of powdery mildew, removing the affected foliage or disposing of the entire plant is recommended. This may prevent powdery mildew from spreading to the remainder of your plants.

How do you prevent powdery mildew?

There are several things you can do to lessen the chances your cucumber plants will become infected with powedery mildew.

  • Grow resistant varieties and allow plenty of room for plants to grow.
  • Avoid overcrowding and check your plants often for any signs of powdery mildew.
  • Water plants by applying water to the soil and avoid overhead watering.
  • Saturate the soil to the root level and do not allow the soil to dry excessively between watering.
  • Water early in the morning to allow foliage time to dry.
​

Natural Remedies for Powdery Mildew

Mix 4 tablespoons of baking soda and 2 tablespoons of horticultural oil (or vegetable soil) to a gallon of water. Add a few drops of dish washing detergent to help the mixture cling to the leaves. Mix thoroughly and apply to your cucumber and squash plants with a sprayer. Coat both upper and lower sides of the leaves. This formula works as a preventative measure, but does little once powdery mildew is present.

When it comes to powdery mildew, prevention is key to your success, as once this disease sets in there, is little that can be done to save your cucumbers and squash. By the time you notice the powdery white surface of the leaves on squash and cucumbers, it is generally too late to save them.
Copyright © 2014 Nannette Richford



  • Home
  • Garden Thyme Blog
  • Themes
    • Butterfly Gardens
    • Moon Gardens
    • Sensory Gardens
    • All About Fairies
  • Flowers
    • Annual Flowers >
      • Alyssum
      • Cosmos
      • Geraniums
      • Marigolds
      • Morning Glories
      • Nasturtiums
      • Petunias >
        • Reviving Petunias
      • Snapdragons
      • Sunflowers
      • Sweet Peas
      • Zinnias
    • Perennial Flowers >
      • Golden Glow (Rudbeckia laciniata ‘Hortensia’)
      • Lupines
      • Purple Coneflower (Echinacea Purpurea)
    • Maine Wildflowers
  • Veggies
    • Warm Season Vegetables >
      • About Beans >
        • Growing Beans
        • Growing Pole Beans
        • How to Make a Teepee Trellis
      • About Corn >
        • Growing Corn
        • What is Baby Corn, anyway?
        • Can you grow corn in containers?
      • Cucumbers >
        • Grow a cucumber in a bottle
        • Growing Pickling Cucumbers
        • Growing cucamelons (Mexican Gherkin)
        • Why do cucumbers blossom but fail to set fruit?
        • Trellising Cucumbers
        • Making Cucumber Relish
        • Powdery Mildew on Cucumbers
      • Melons
      • Peppers >
        • Growing Peppers
      • Squash >
        • Growing Zucchini
        • Spaghetti Squash
      • Tomatoes >
        • How to Harden Off Tomato Plants
        • How (and when) to Prune Tomatoes
        • Magnesium Sulfate (Epsom Salt) for Tomatoes
        • Blossom End Rot in Tomatoes
        • Growing Cherry Tomatoes in Hanging Baskets
        • 4 Best Tomatoes for Short Seasons - Early Tomatoes
        • 5 Early Maturing Tomatoes for Short Season Gardening
        • How to Ripen Green Tomatoes
        • How to Make Sun-Dried Tomatoes at Home
        • How to Grow a Pomato Plant
    • Cool Season Vegetables >
      • Cole Crops
      • Greens >
        • How to Grow Spinach
        • How to Grow Malabar Spinach
        • How to Grow Swiss Chard
        • Harvesting and Cooking Beet Greens
        • How to Grow Microgreens
      • Onions & Garlic >
        • How to Grow Garlic
        • How to Grow Onions
      • Peas >
        • Growing Garden (shelling) Peas
        • Growing Sugar Snap Peas
      • Potatoes >
        • How to Grow Potatoes in Containers
        • How to Grow Potatoes in Hay Bales
      • Root Crops >
        • Growing Beets
        • How to Grow Carrots
        • Turnips vs Rutabagas
  • Herbs
    • Growing Basil
    • Growing Chives
    • Growing Lavender
    • Herbal Tea Garden
    • How to Grow a Culinary Herb Garden
    • How to Grow Herbs in Sponges
    • Colonial Herb Garden - Classroom Project
    • Herbed Butter
    • Making Herbed Oils
  • Gardening Basics
    • Seed Starting Basics
    • Grafting Basics
    • Soil >
      • Starting a New Garden
      • How to Prepare Soil
      • How to Test Soil Drainage
      • What Type of Soil Do You Have
      • Soil Mix Recipe for Containers
      • How to Make Compost Tea
      • How to Use Mulch
  • Garden Pests
    • How to Control Japanese Beetles
    • How to Control Blister Beetles
    • How to Get Rid of Colorado Potato Beetles
  • Birds
    • Hummingbirds >
      • DIY Hummingbird Feeders from Recycled Bottles
      • Annuals for Hummingbird Gardens
      • Perennials for Hummingbird Gardens
    • About Birdseed
    • Choosing a Birdfeeder
  • Fiddleheads and Fairies
  • About Us
  • Contact Us
  • How to Marinate Roasted Vegetables