Try Our Recipe for a Homemade Baking Soda Spray
One unwelcome visitor to my garden at this time of year is powdery mildew. Here’s how to control this plant disease with natural remedies, including a homemade baking soda spray treatment.
Signs of Powdery Mildew
It starts as white patches on the leaves of squash, lilacs, phlox, bee balm, and other plants, making them look like they have been dusted with baby powder. Early on, it wipes off or washes away, only to return again.
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Eventually, the affected leaves turn yellow and die on many plants while others continue to soldier on.
So far this year, only our squash has been affected.
Thankfully, there is no sign of it on other susceptible plants such as phlox.
Causes of Powdery Mildew
The lack of powdery mildew on my phlox is probably due to the fact that it is not caused by just one fungus but by several different species that affect different kinds of plants. The powdery mildew that you find on your squash is not the same as the mildew on your beans or roses.
Cucurbits such as pumpkins, squash, cukes, and melons have three different powdery mildew fungi gunning for them that can thrive in both humid and dry weather. The spores of the fungi are windborne and can’t really be avoided. No wonder the squash gets hit every year!
Remedies for Powdery Mildew
There are lots of home remedies, but researchers have found that simply spraying with plain water weekly can be effective. The spores like humidity but hate rain and water. They can’t germinate or grow if the leaves are wet, which is the opposite of what most gardeners, including me, think.
One season, I tried to defeat powdery mildew by planting squash in our high tunnel, thinking that if I could keep the leaves dry, they would not be affected. Naturally, they got the worst case of powdery mildew I have ever seen! It was the perfect place for it to thrive: high humidity and no rain hitting the leaves. Another lesson learned the hard way!
If you decide to try a home remedy rather than plain water, there are several that have been proven to be effective if used early. They can slow or stop the spread early on, but once the fungi are established in the leaves, they won’t eliminate it.
Homemade Baking Soda Spray for Powdery Mildew
Many of these remedies include baking soda. Just be aware that baking soda can burn plants, and it can build up in your soil, potentially causing deficiencies in calcium, magnesium, and iron. Potassium bicarbonate can be substituted for baking soda. Test these sprays on a small area first to ensure they do not damage your plants.
- Mix 1 tablespoon baking soda with 1 tablespoon vegetable oil and 1 teaspoon dish soap in 1 gallon of water.
- Mix 4 tablespoons baking soda with 2 tablespoons of Murphy’s oil soap in 1 gallon of water.
- Mix 2 to 3 tablespoons vinegar with 1 gallon of water. Be sure to test this first because vinegar can burn plants.
- Neem is an organic fungicide. Follow the instructions on the label.
- Mix 1 part milk with 10 parts water.
- Some folks swear by mouthwash as an effective fungicide, but it is not organic. They recommend 1 cup of mouthwash to 3 cups of water.
To keep the fungi from developing a resistance to your homemade spray, it is recommended that you alternate remedies each week. Use baking soda one week and milk the next. Whether spraying with water or a home remedy, do it early in the day so the leaves can have a chance to dry before evening.
When adding new plants to your flower beds, look for mildew-resistant varieties. Don’t over-fertilize with high-nitrogen fertilizers since soft new growth is very susceptible to infection. Space plants are far enough apart to promote good air circulation. If the infection starts in the lower leaves, snip them off. Make sure plants get enough direct sunlight. Prevention is the best medicine!
→ See more about Powdery Mildew Control.
Have you experienced powdery mildew? How do you manage it? Tell us in the comments!
Robin Sweetser
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What do you recommend spraying for powdery mildew on phlox, bee balm & milkweed?
Hi Julie,
There are many different remedies for powdery mildew, including the ones referenced above and the ones in this link https://www.almanac.com/pest/powdery-mildew . Most fungicide options are best used before powdery mildew is present and also can cause other issues in the garden when it comes to pollinators and negatively affecting certain plants. Make sure to research any product you plan to use on specific plants.
Many remedies have been used to slow or stop the spread when used early on, but once the fungi is established it can be difficult to eradicate. It is best to work toward prevention of powdery mildew early in the season before the conditions—warm, dry climate with fairly high humidity—are present. When planting in the future, look for powdery mildew resistant varieties and make sure to space new plants to allow for adequate air circulation. For current plantings, you can prune in a way that supports better air flow and allows more light to reach your plants, limiting the conditions powdery mildew needs to spread. For severe infestations, it might be best to remove the plant to protect the rest of your garden.
You will also want to check plants that have been affected by powdery mildew at the end of the season and remove any areas where it is present because dormant spores can overwinter on old vegetive material or weeds.
I used water and dishwashing liquid. Very effective. I sprayed 3 times only on our tomatoes and eggplants 3 days apart and it never came back. We have very healthy tomatoes.
I used simple mix of Dawn and water immediately after discovering the mildew, soaked the four rose bushes thoroughly,next morning completely gone, amazing idea people, thank you
What was the ratio
I researched and learned that a cucumber vine life-span is 70-80-days. My cucumber vine did die; however, it was past 70-days, had produced many cucumbers and I feel it died from age and not from the spray.
Not sure about using baking soda. I had a beautiful cucumber that produced a colander of cucumbers each week. It began to get powdery mildew. I used the recipe according to instructions; sprayed early in the morning. The days afterward were cloudy and the vine looked healthy. Two weeks later, however, the vine is turning yellow; appears to be dying and there are no cuke. I have kept up the watering. I will begin watering with 20-20-20; maybe the baking soda leached out important nutrients...Not sure what happened?
I started using Bee Safe 3-in-1 Garden Spray (Organocide) on my squash plants when I saw powdery mildew. The white spots faded within a day and I simply spray every few days as more appears (which is not very much). This product contains sesame oil so may be available in other forms as well.
I’m not sure of the most effective way to get rid of this. There are also repeated holes. I did find micro black and pale yellow dots on the undersides. Help needed re rust and yellow leaves on my cake leaves and okra. Thanks
Every year my peony bushes get powdery mildew really bad. Is the water/other additives you recommend spraying good for peonies??
