Treating Plants with Powdery Mildew

This common fungal disease can affect nearly all types of plants. This guide is about treating plants with powdery mildew.

Powdery Mildew on Plants
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Powdery Mildew on PlantsIf 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.


  • Start by selecting and planting mildew-resistant plants.
  • Avoid watering plants from overhead to steer clear of splashing leaves.
  • Selectively prune stems and branches to improve air circulation around plant leaves.
  • Eliminate environmental stress caused by water or soil deficiencies, which leave plants more susceptible to disease.

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!

CommentMoreRead More...Was this helpful?Helpful? Yes

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

CommentMoreRead More...Was this helpful?Helpful? Yes

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

AnswerWas this helpful?Helpful? Yes

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

ReplyWas this helpful?Helpful? Yes
Read More Answers...

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.

    CommentWas this helpful?Helpful? Yes

    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.

    leaf covered with powdery mildewmildew on peasleaf spotted with mildew
      CommentWas this helpful?Helpful? Yes

      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

      AnswerWas this helpful?Helpful? Yes

      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.

      ReplyWas this helpful?Helpful? Yes

      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

      AnswerWas this helpful?Helpful? Yes

      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.

      ReplyWas this helpful?Helpful? Yes
      Home and Garden Gardening Plant HealthMay 30, 2012
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