Treating Plants with Powdery Mildew

If you garden long enough, sooner or later you'll find yourself dealing with powdery mildew problems. This common fungal disease can affect virtually all types of plants. Fortunately, other than slowing down growth, reducing yields, and looking terrible, it rarely kills affected plants. Here are some ways to tackle the problem organically.


Symptoms and Effects

If your plants have a white to grayish powdery coating on the upper surfaces of the leaves, the problem is most likely powdery mildew. Once a plant's leaf surface becomes covered with patches of mildew, its ability to produce food (photosynthesis) is reduced and it becomes weak. Leaves are often shed prematurely, and in severe cases the plant may fail to produce fruit.

There are many types of powdery mildew, all of which spread by microscopic spores. These spores can live for years in leaf debris or in the soil, and are carried to plants by wind, insects, and splashing water. Conditions that favor the spread and growth of powdery mildew include a lack of air circulation around plants (especially in the shade), dry weather, and temperatures between 60 and 80 degrees F.


Organic Treatments

Baking Soda: This homemade remedy is easy and inexpensive to make, and very effective at preventing powdery mildew. Mix together 3 tablespoons of baking soda (sodium bicarbonate), 1 tablespoon of Murphy's Oil Soap (or light horticultural oil) and 1 gallon of water.

Spray a fresh batch of the mixture on the tops and bottoms of leaves every 7 to 10 days. Because oil combined with the heat of the sun can damage plant tissues, it's wise to test the solution on a few leaves before using it in large quantities.

Water: This low-tech approach must be done consistently to work effectively. Unlike indoor mildew, powdery mildew hates water and spreads readily on dry leaves. The spore plugs must embed themselves in leaf tissue to grow, which they can't do on slippery, wet leaves.

Spray down the leaves with the garden hose daily. Make sure you do this early enough in the day so that leaves dry out before evening, otherwise you'll be swapping one fungal disease for another.

Compost Tea: When used as a foliar spray, compost tea has both insecticidal and fungicidal properties. Place a gallon of well-aged compost in a 5-gallon bucket and fill it with water. Stir well and let sit in a warm place for 3 days.

After three days, siphon off the liquid tea by filtering the mixture though a burlap sack. Pour the tea into a hand held sprayer and apply to leaves in the evening.

Remove affected leaves and discard severely affected plants. Use a plastic bag to carry the plant debris out of the garden. Spores can live for years waiting for the right growth conditions, so either burn the waste or discard it in the trash. Don't compost it!

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More Solutions

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A good solution to get rid of this powdery mildew is to make a solution of dry powered milk and spray your plants. This is a tip I learned at a Master Gardener class. It works!

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There are many articles posted on the Internet reporting that ordinary cows milk diluted with water to about a 10 % solution and sprayed on plants is highly effective as a preventative and as a treatment for various types of powdery mildew.

powdery mildew on plant leaves

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I's that time of year again, the garden and the garden pests are back with a vengeance! This is what white mold looks like. It destroys cucurbit crops such as pumpkins, cucumbers, and peas. To date we have tried everything to rid ourselves of this.

leaf covered with powdery mildew

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10 Questions

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I am very inexperienced in gardening. There is a white powdery look and white flecks on the underside of a sweet potato vine. Is this powdery mildew? The white flecks are not insects. But I do not know what they are.

Hardiness Zone: 10b

By lynn salem from South FL


November 11, 20090 found this helpful

Powdery mildew. The scourge of the garden. Sometimes fatal but mostly just annoying, it covers foliage with a white powder that makes plants look bad.

Two things you can do to help keep powdery mildew from forming on your plants: space them far enough apart so the air can circulate freely around them and do not water after noon. Wet foliage after sundown is a favorite host of mildew spores.

It's not necessary to mount a full frontal assault with a host of toxic chemicals. Powdery mildew can be treated and sometimes even eradicated by using common household ingredients. Below are 7 home made preparations you can use to treat powdery mildew in your garden.

But first, some general instructions for treating white powdery mildew with anti-fungal preparations: Hose off the plants with a strong spray from the hose prior to treating with these preparations to remove as much mildew from the surface as you can. Be sure to cover all parts of the plant with the treatment spray, including the undersides of the leaves and the stems. Spray some on the soil around the plant as well. Finally, spray for mildew early in the morning before the sun rises too high in the sky. Spray plants once or twice a week in dry weather and more often if rainy.

Apple Cider Vinegar. Mix 3 tablespoons of cider vinegar with one gallon of water. Also works on black spot on roses and aspen trees.

Baking Soda. Mix 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil and one gallon water. Shake well then add 1/2 teaspoon of Castile soap. Shake the container as you spray your plants to keep the oil and water from separating.

Chives. Use a bunch of freshly cut chives, about as many as you can hold in your closed hand without dropping them. Chop the chives and place in a heat-proof glass container. Cover with boiling water and let sit until cool. Strain.

Corn and Garlic. Take a handful of corn leaves, along with a handful of clematis leaves and as many of the papery outer skins of garlic as you can. Pulverize in blender or food processor. Mix in enough water to make a thin liquid. Let the mixture sit for an hour, then strain. This also works as a preventative against powdery mildew.

Horseradish. Place one cup of chopped roots into a food processor and process until finely chopped. Combine with 2 cups of water in a glass container. Let sit for 24 hours then strain and discard solids. Mix strained liquid with 2 quarts of water. This mixture is also an effective preventative against molds and mildews.

Hydrogen Peroxide. Spray regular hydrogen peroxide (the kind from the drugstore, not the food grade kind) full strength on the affected plants. Do not spray on newly transplanted plants or young seedlings until they become well established. Test on a small area of the plant and wait 24 hours to see if it has any negative reactions to the hydrogen peroxide. This works as both a treatment and a preventative.

Milk. Mix one part of milk with 2 parts of water. Spray every 3 to 4 days at the first sign of mildew. Milk changes the pH of the surface of the plant leaves and prevents mildew from adhering to them. Can also be used as a preventative measure. Good luck.

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November 12, 20090 found this helpful

One thing that I found helps with powdery mildew is to make a solution of dry powder milk, and spray your plants. Learned this at a mg. class

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November 12, 20090 found this helpful

I've seen this on my plants. If it's not powdery mildew it's the residue of the bad bugs that the good bugs ate.

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November 12, 20090 found this helpful

If this white powder is on the bottom side of your leaves, it may be mealy bugs and they are easily washed off. You can use clear water or mix a drop of dishwashing liquid with it. Keep a close watch on this plant as they may show up again and mealy bugs will kill the plant. They will move to other plants they like so watch the neighbor plants.

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November 13, 20090 found this helpful

I use the milk method but I use skim milk full strength.

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November 15, 20090 found this helpful

Go to your Nursery, Home Depot or Lowe's for some plant treatment that will kill the white powder.

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My perennial phlox has white moldy leaves all over. Should I cut them down to the bottom? I sprayed fungicide on them, but it didn't help.


June 6, 20170 found this helpful

Cut off infected parts and spray the rest of the plant with horticultural oil.

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June 6, 20170 found this helpful

From SFGate:

Sulfur or copper fungicide will help treat powdery mildew on plants such as garden phlox. However, before treating the plant with the fungicide, test it on an inconspicuous area of the garden phlox and wait 24 hours.

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June 9, 20170 found this helpful

Most likely your plant will recover with just a little TLC. White powdery mildew is a fairly common problem and just takes a good cleaning and spraying with an effective fungus spray that is safe for your plant.
Here is a good site that has a lot of information about this fungi and even some home solutions that usually work as well as store bought products.

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January 14, 2015

There has got to be something you can do to get rid of the powdery mildew. I have tried compost, mulch, and last year I put in some tomato cages to keep them off the ground. They had the most beautiful vines, some 5 feet tall, but when the fruit set all the vines died! I wish I could send a pic of the vines.

By Vicki


June 30, 20180 found this helpful

This article explains the why and prevention better than I can:

I don't like that it suggests chemicals to get rid of it. Theyvare terrible for the watershed and can harm pets and small children.

A better solution is a simple mix of 1 teaspoon to one quart of warm but not hot water, shake up in a clean spray bottle and spray down the plants in the cool of the morning.

Hope this helps!

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I recently noticed that one of my succulent houseplants, a kalanchoe, has powdery mildew on the leaves. I just moved and it is in a new location, but nothing else has changed. How to I treat the leaves? They now have brown spots where I have wiped it off. Thank you for your suggestions.

By R Barbara from Bremerton, WA


July 23, 20110 found this helpful

I've never treated succulents for powdery mildew, but have other plants using a fungicide purchased at the garden centre. Check your local extension website, or talk to the staff at the nursery to see what they suggest.

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This is the second summer I've grown zucchini and yellow squash in my garden. Both years the leaves become covered with powdery white mildew. Eventually the bottom leaves die and the new leaves soon become mildewy as well.

I have had two different water systems, underground that waters only the roots, and above ground, but only watering in the morning so the leaves get dry. It didn't seem to make any difference, they were covered with mildew with both systems. I don't want to use a chemical fungicide unless there's no other option to get good healthy leaves. I don't want to eat fungicide. I would be grateful for any help.

By LeeAnne67 from Bothell, WA


September 10, 20110 found this helpful

I feel your pain. I've been plagued with powdery mildew for over two decades. It is nearly impossible to get rid of because it lives in the soil from year to year and is both air borne and water borne. One of my yards is so infested with it that I cannot grow any vegetables there at all. It is extremely contagious and easily transmitted by the hands and gardening tools.

The only thing I've learned to do is manage it, somewhat, by eliminating flowering plants that easily succumb to it - morning glories and sunflowers, for example. It attacks nearly all soft leaved plants, so your squash is easy prey. Remove infected leaves immediately and harvest very early, not letting the fruit remain on the vine too long, then pull up the plant when the mildew begins to overtake the it. I've managed to grow squash quite successfully with this kind of diligence. Also, areas of the garden that get the longest hours of full sun seem to thwart the invasion. If anyone knows a cure I'd sure like to know about it.

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My hibiscus plant has a white powdery substance on the leaves and stems. The leaves turn yellow and fall off. How do I get rid of it? What is it?

By Dawn H

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