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Treating Plants with Powdery Mildew

Category Plant Health
Powdery Mildew on Plants
This common fungal disease can affect nearly all types of plants. This guide is about treating plants with powdery mildew.


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By 6 found this helpful
May 10, 2011

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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By 6 found this helpful
May 28, 2011

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!


By jeannette from West Palm Beach, FL

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August 11, 2014

There are many articles posted on the Internet reporting that ordinary cow's 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.

Most of these reports came from the average home gardener. I have been looking for a more credible source. I found one just today. A 2002 Science News article by Janet Raloff cites the findings of Peter Crisp with the Department of Applied and Molecular Ecology, University of Adelaide.

The findings were that diluted milk was very effective for treating grape vines infected with powdery mildew. The idea to use milk came from its effectiveness in the treatment of powdery mildew on zucchini.

My yellow crookneck squash are infected. While it's a little late in the season (and too late to consider a preventative), I am going to start a regular spraying routine with diluted milk. I hope to see if there is a significant reduction in the mildew by the end of the growing season.

If you have any information on this subject, such as other reputable studies or the results of your own home trials, I do hope you will consider posting them here.

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By 0 found this helpful
August 6, 2014

It'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. We have cut off diseased leaves, sprayed them with neem oil, compost tea, water, milk, and baking soda. So far nothing at all rids the cucurbits of this disease.

It makes the leaves brittle and it gets in the stems. Then the plant starts to wither and slowly die off. It's highly contagious. If you try cutting off leaves treat the cutters with alcohol wipes or wash them in soapy water after each cut. Also keep a bag handy and place all cuttings in the bag and throw it away. Do not compost it! They say that warm humid conditions cause it, which is the typical summer weather where we live so its only a matter of time most years. I hope to try to combat it next year with tri weekly treatments of compost tea on the leaves.

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Ask a QuestionHere are the questions asked by community members. Read on to see the answers provided by the ThriftyFun community or ask a new question.

By 0 found this helpful
November 7, 2009

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 from South FL

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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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By 0 found this helpful
June 6, 2017

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.

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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.

https://www.the … y-mildew-1402500

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By 0 found this helpful
September 6, 2011

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

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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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By 0 found this helpful
July 15, 2011

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 Barbara from Bremerton, WA

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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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By 0 found this helpful
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

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By 0 found this helpful
May 29, 2012

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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