Keep Powdery Mildew Away with This Grocery Staple You Probably Already Have at Home

Powdery mildew is a common plant disease that affects ornamentals and edible crops, causing powdery splotches on plant leaves and stems. While gardeners often rely on store-bought fungicides to treat powdery mildew, homemade sprays made with milk and water can be just as effective. If you maintain an organic garden or want to reduce gardening costs, here's how to treat powdery mildew with a simple milk spray you can make at home.

What Is Powdery Mildew?

Powdery mildew is a common plant disease caused by several types of fungi that naturally exist in gardens. They transfer from plant to plant on the wind or via contaminated gardening tools. While powdery mildew problems are rarely fatal to plants, they can cause unsightly patches of gray or white powdery fungus to spread over leaves, stems, buds, fruit, and flowers. It can also make plants less productive because it saps energy from the plant and blocks sunlight.

Powdery mildew problems can occur at different times of the year, but they’re most common during spring and summer when cool nighttime temperatures and humid weather encourage mildew spores to spread. Stress, low light, and overcrowded growing conditions with poor airflow can also increase a plant’s susceptibility to mildew issues.

Some plants that are particularly vulnerable to powdery mildew include:

• Squash
• Melons
• Pumpkins
• Cucumbers
• Parsley
• Mint
• Bee balm
• Peonies
• Sunflowers
• Dahlias
• Roses

How Milk Sprays Work

Studies have shown that milk sprays are effective against powdery mildew. However, why this treatment method works is still a matter of debate.

Some argue that milk changes the pH of plant leaves, making them less hospitable to powdery mildew. Others suggest that milk sprays encourage the growth of beneficial microbes that naturally keep mildew from growing. Either way, milk sprays are a valuable tool in the organic gardener’s arsenal, and they’re more budget-friendly than store-bought fungicides.

How to Make a Mildew Spray with Milk

Current studies have focused on the effectiveness of whole-fat cow’s milk against mildew, and they’ve not explored whether skim or plant-based milks produce the same results. For this reason, use raw, pasteurized, or powdered cow’s milk with a high-fat content to make the milk spray.

To make a simple milk spray, mix 2 parts milk and 3 parts water in a spray bottle or garden sprayer. Some growers may also want to add a bit of neem oil or baking soda for an extra mildew-busting punch, but this is optional.

How and When to Apply Milk Sprays

Milk sprays and most other fungicides work best as preventives, and they’re not as effective against established mildew infestations. That's why it’s best to start spraying your plants at the beginning of the growing season or as soon as the first signs of mildew problems appear. If particular plants in your garden suffered from mildew in the past, spray those plants first, as they’ll likely develop mildew again if you don’t.

Milk sprays only work in areas where they directly contact plant leaves and stems, so it’s essential to thoroughly saturate plants when applying them. These sprays work best when applied in full sun.

Use a garden sprayer or a spray bottle to apply the milk spray to the tops and undersides of plant leaves, ensuring they are thoroughly drenched. Allow the milk spray to dry on the plant and then reapply it every one to two weeks through the growing season until humidity levels fall in late summer or autumn.

Tips for Reducing Powdery Mildew Problems

Combining these techniques with regular applications of milk sprays can help ensure you never have to tangle with powdery mildew again.

• Follow spacing guidelines. One of the primary reasons plants develop powdery mildew is overcrowding. Ensuring your plants are spaced correctly in the garden allows more air and sunlight to reach their leaves and naturally reduces mildew problems.
• Prune wisely. Pruning the worst-hit leaves off mildew-infested plants before using milk sprays can make the sprays more effective. You can also use pruning preventively to open up the center of overgrown plants and enhance airflow.
• Disinfect garden tools. Mildew spores can hitch a ride on pruners and other gardening tools, allowing them to move from plant to plant. To avoid this, disinfect gardening tools that have come into contact with mildew-infested plants using rubbing alcohol or a 10% bleach solution.
• Avoid overhead watering. Wet plant leaves are more likely to develop mildew problems. Therefore, it’s best to water plants at the soil line using a garden hose, drip irrigation, or a soaker hose system.
• Choose disease-resistant plants. Some plant varieties are naturally more resistant to powdery mildew than others. If you have ongoing mildew problems in your garden, selecting resistant cultivars can help.
• Do a fall garden cleanup. Mildew spores can overwinter in old leaf litter and infested plant material and then reinfect new plants in spring. Avoid this by cleaning out and destroying old plant debris in fall and keeping diseased plant matter out of compost piles.
• Keep plants healthy. Ensuring that your plants receive the proper amount of light, water, and fertilizer is key to preventing mildew problems. Healthy plants are much better at resisting powdery mildew than stressed ones.