Powdery Mildew

How to Prevent and Control Powdery Mildew

Powdery Mildew2
Photo by Pollinator: Wikimedia Commons

Wondering about that white fungus on your plant? The fungal disease powdery mildew is a common problem in gardens, infecting a wide variety of plants and reducing the quality and quantity of flowers and fruit.

What Is Powdery Mildew?

Powdery mildew is a fungal disease that affects a wide variety of plants. There are many different species of powdery mildew, and each species attacks a range of different plants. In the garden, commonly affected plants include cucurbits (squash, pumpkins, cucumbers, melons), nightshades (tomatoes, eggplantspeppers), roses, and legumes (beanspeas).

When the fungus begins to take over one of your plants, a layer of mildew made up of many spores forms across the top of the leaves. These spores are then carried to other plants by the wind. Powdery mildew can slow down the growth of your plant and, if the infection is severe enough, will reduce fruit yield and quality. 

How Does Powdery Mildew Spread?

Powdery mildew spores typically drift into your garden with the wind, but if you’ve had powdery mildew occur in the past, new outbreaks may also come from dormant spores in old vegetative material or weeds nearby.

Unlike many other fungal diseases, powdery mildew thrives in warm (60-80°F / 15-27°C), dry climates, though it does require fairly high relative humidity (i.e., humidity around the plant) to spread. In cooler, rainy areas, it does not spread as well, and it is also slowed down by temperatures higher than 90°F (32°C). It tends to affect plants in shady areas more than those in direct sun, too.

 

    Identification

    How to Identify Powdery Mildew Damage

    • Plants infected with powdery mildew look as if they have been dusted with flour.
    • Powdery mildew usually starts off as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit.
    • Powdery mildew usually covers the upper part of the leaves, but may grow on the undersides as well.
    • Young foliage is most susceptible to damage. Leaves turn yellow and dry out.
    • The fungus might cause some leaves to twist, break, or become disfigured.
    • The white spots of powdery mildew will spread to cover most of the leaves or affected areas.
    • The leaves, buds, and growing tips will become disfigured as well. These symptoms usually appear late in the growing season. 

    powdery-mildew-identification.jpg
    Powdery mildew first appears as small white spots on the upper part of the leaves. Photo Credit: The Regents of the University of California, UC Davis.

    Control and Prevention

    How to Prevent Powdery Mildew

    As with all pests and diseases, the best means of controlling powdery mildew is proactive prevention. 

    • Choose plants for your garden that are resistant to powdery mildew. Many mildew-resistant varieties of cucurbits (melons, cucumbers, squash, etc.) have been developed and can be bought from major seed suppliers.
    • Plant in sunnier spots, as powdery mildew tends to develop more often in shady areas.
    • Selectively prune overcrowded areas to increase air circulation around your plants; this helps to reduce relative humidity.
    • Watering from overhead can help to wash spores off leaves. Note, however, that wet foliage can often contribute to the development of other common diseases, so it’s best not to rely on this as a prevention tactic.

    How to Control Powdery Mildew 

    • Consider spraying infected plants with protectant (preventative) fungicides. Effective organic fungicides for treating powdery mildew include sulfur, lime-sulfur, neem oil, and potassium bicarbonate. These are most effective when used prior to infection or when you first see signs of the disease.
    • If you don’t want to use chemical fungicides, try spraying your plants with a bicarbonate solution:
      • Mix 1 teaspoon baking soda in 1 quart of water. Spray plants thoroughly, as the solution will only kill fungus that it comes into contact with.
    • Once plants are heavily infected, it’s very difficult to get rid of the disease, so focus on preventing it from spreading to other plants. Remove all infected foliage, stems, and fruit and destroy them, either by throwing them in the trash or by burning. Remember, do not compost any infected plant, as the disease can still be spread by the wind and persist in the composted materials.

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    Reader Comments

    Leave a Comment

    Red Spider Mite on Hydrangea

    The Editors's picture

    Mite infestations often occur when plants are stressed from insufficient water, so be sure you are watering enough. General purpose insecticides can exacerbate the problem. Instead use an insecticidal soap according to the directions on the label to knock the population back.

    A source of mould on cucurbits

    ILLEUS GALBULA: little black beetle with with yellow spots (looks like a ladybird, but with louse-like larvae) eats mould, but unfortunately I took a couple of seasons to realise that they also spread mould spores in their vicinity to provide themselves with a food source. :( There isn't enough Baking Soda, the plant dies .......

    White Mildew

    Can this white mildew become solid, and fall to the ground like crystal: When stepped on crushes into white powder?

    White mildew

    We have clumps of white mildew on the dirt around some of our plants and on the trunk of one of our ferns, which is virtually impossible to remove other than spraying it with something. What to spray the fern with is the question, and can we use the same solution on the ground?

    Thank you,
    Elrene

    Powdery mildew spray

    The Editors's picture

    The fern should be safe if sprayed with the solution described above and sure, spray it on the ground:

    If you don’t want to use fungicides, try spraying your plants with a bicarbonate solution:

    • Mix 1 teaspoon baking soda in 1 quart of water. Spray plants thoroughly, as the solution will only kill fungus that it comes into contact with.

    pear tree

    My pear tree when I moved in to my house last year had some leaves, by this time last year it had small fruit growing, now it seems that it is dying. No fruit has grown or there hasn't been any leaves. I don't know what has gone wrong with my pear tree. The pear tree is in my back yard. I also have a tree, it grows small green pea shape balls, but this year it hasn't grown anything either, and seems to dying only partial of the tree has leaves. but, I feel it end is at hand. What could have come on my property to kill my tree?

    Dying Trees

    The Editors's picture

    Hi Gregorio,

    Since both trees are failing, I suspect it is a soil-related issue–there are many pathogens that live in the soil that can kill different tree species. There is really only one way to know for sure, and that is to have your soil tested by a cooperative extension agent, who will be able to identify any problems and provide recommendations.

    Do I need to treat pumpkins

    Do I need to treat pumpkins (whose leaves had powdery mold) when I harvest them? I'm wondering if I should wipe them, or at least spray the stems, with a disinfectant.

    Powdery mildew should not

    The Editors's picture

    Powdery mildew should not affect your pumpkins now that the skins are hardened and cured. It is a fungus that grows on the surface of leaves and some fruit.

    I have powdery mildew on my

    I have powdery mildew on my pumpkin plants (took me a while to realize what it was) and I have 8 pretty big pumpkins on them at the moment. half the leaves have died and we still have 1.5 months to go before halloween comes along. Can I save my pumpkins? if yes how? do I need to cut them off right away or can I leave them to mature a bit more? I dont want to cut them off now and they rot before halloween comes! Thank you!!

    Test to see if your pumpkins

    The Editors's picture

    Test to see if your pumpkins are mature: press the end of yout thumbnail into the flesh of the fruit; if little indentation is left in the fruit, the pumpkin is mature.
    You could target the powdery mildew with spray, if it is not covering most of the plant. Consult a nursery for a recommendation.
    When the plants are done, remove all of the decayed plant material to reduce overwintering fungus. Avoid fertilzing with too much nitrogen. Next season, avoid crowding plants.

    my pumpkin plant is severely

    my pumpkin plant is severely infested with white powdery mildew after a week or two of rain. With more rain to come, is there a chance that spraying the leaves will help save the vines, or should I tear them out before it spreads?

    Several sources we consulted,

    The Editors's picture

    Several sources we consulted, Jesse, say that your pumpkins will be ok, esp this late in season and esp if they are strong and healthy otherwise. Dampness is not the best thing. Spraying, esp  with rain coming that may wash off the spray, may not be the best solution. If you do want to spray, consult a nursery about horticultural oil of a biological fungicide.
    In future, consider planting resistant varietes, give the plants plenty of room to grow, and certainly full sun.
    Here's hoping you get this before the rains!

    I to am having trouble with

    I to am having trouble with black spots and powdery patches, thanks for all the information...My question can the water from a water softner harm roses or any plants?I planted 20 roses lost 10 and other annuals.......

    It's OK for a little while

    The Editors's picture

    It's OK for a little while but not advised for the long-term due to the build-up of sodium. Water softeners take away calcium and magnesium and then leave sodium in the water. It is better to use the outside tap runs off the mains. Rain water, tap water, purified water, and boiled water are better options.

    I have powdery mildew on my

    I have powdery mildew on my sunflowers and it killed them off and I would like to know if it will go away or do I have to remove my dead sunflowers and plant new ones next year? I really hope next year they will come back or can I do something now before the summer ends? I live in Tampa Fl where it is the start of the rain season every afternoon.

    Hi Jessica, You need to pull

    The Editors's picture

    Hi Jessica,

    You need to pull up and destroy the dead sunflowers.
    You can try to plant new seeds in a different area of your garden. Plant the seeds in full sun and space them so that they will have good air circulation. For prevention spray with a neem oil spray or a mixture of 1 teaspoon of baking soda blended into a quart of water.

    I bought a lilac bush (a

    I bought a lilac bush (a young plant) a few months ago and a few days later I noticed it had powdery patches on it. I suspect it is powdery mildew. I planted it in my backyard a month ago. I didn't know what to do about the powdery patches so I haven't done anything about it yet. My lilac bush hasn't grown at all since I bought it and this concerns me. It is in partial sun--it gets the sun from the morning, and is shaded by trees in the afternoon. Any suggestions? Does it just take forever to grow? Will the powdery mildew kill it if I don't do anything? Please reply with suggestions. Thanks.

    Your lilac tree is still

    The Editors's picture

    Your lilac tree is still young and you just planted it. It will grow more in the spring and next summer. Powdery mildew is common on lilacs after a hot humid summer. It's not going to hurt your bush. Lilacs need about 6 hours of full sun a day to bloom well. Go to our lilac page to find more tips about growing lilacs.
    http://www.almanac.com/plant/l...

    hey i had powdery mildew bad

    hey i had powdery mildew bad last year and my buddy had the same issue so we figured a little cure searching was in order so after losing all of my tomatoes and most of my peas i found this stuff called cuh2o and i guess all this is, is copper and water when i called the number the people told me it was used for years and so i asked whats so special they literaly just told me its the copper suspended in watter and its pattend or whatever yadda yadda epa yada all that jazz and so i says send me a bottle and man with in the week i called em back and gave them my blessing cuz it kicked butt i mean i now have no sings of powder and it dont leave the nasty residue but any who ill share the number with you so u can combat and rid your plants of mildew your not alone with the problem and it dose suck the life out of em but ya heres the number 616-226-6539

    how do I keep Beatles off

    how do I keep Beatles off rose bushes

    This is our powdery mildew

    The Editors's picture

    This is our powdery mildew page.  You can find more information on our Roses page as well as our Japanese Beetles page here:
    http://www.almanac.com/plant/r...
    http://www.almanac.com/content...
    You need to handpick these beetles and drop into pails of soapy water. You could also place fine netting over the rose bush.  Another idea is to get ride of the grubs in the lawn with Milky Spore. Finally, you could use an insecticide; speak to your local garden center about what's approved in your area.

    The top of our raspberry

    The top of our raspberry plants are dieing. what causes this?

    Last year was my first year

    Last year was my first year growing a garden by myself. All the vine type plants (pumpkins, squash, melons, etc.) were killed by powdery mildew. They were doing great at first, by the end of summer the powdery mildew spread and rotted all the fruit and veggies. It was suggested to me that I burn the garden last fall, but I didn't get a chance to do it. In a month it will be time to plant the garden again. Will the mildew come back because I didn't burn the garden? Is there anything I can do now before I plant to prevent the powdery mildew from returning?

    Some sources advise burning

    The Editors's picture

    Some sources advise burning the infected plant materials that were affected with powdery mildew in the same season. Hopefully, you at least cleaned the garden of any infected plants. If you have not yet, do that as soon as you can and avoid shaking any residue that might be infected into this year's garden bed. The spores can overwinter on affected plants and it can fall off as you move plant residue.
    As for this season, plant resistant varieties for better results. Plant in full sun. Avoid excess fertilizer (hard to know how much for you would be "excess"; follow fertilier guidelines). Provide youor plants with good air circulation; give the adequate (or slightly more) space between each.
    If you do see signs of powdery mildew returning, prune to remove the infected branches or shoots as soon as you can. 
    We hope you have a happy harvest this year.

    Pumpkins are heavy feeders

    Pumpkins are heavy feeders and I would plant them in a different area this year. Be shure to feed your last year's garden with a good compost or other natural amendments. I always rotate heavy feeders every year and plant a cover crop to till in for the following year. Burning diseased plants or putting them in the trash is a good idea. I wouldn't plant a heavy feeder in the same spot for two or three years. If you don't have the room to rotate then feed the soil heavily. I like a mulch of at least 6 to 8 inches but pull it aside to get your plants into the soil. Happy gardening!

    My Rose bush has Black Spot.

    My Rose bush has Black Spot. Is there a home remedy to remove the Black Spot?
    Thank You

    First, prune off the damaged

    The Editors's picture

    First, prune off the damaged parts of the plant and dispose of the diseased material in bags or burn it. Do not add to the composter.
    One home remedy is a solution made with baking soda: dissolve 1 teaspoon baking soda in a quart of water, add a few drops of liquid soap to the mix to help it cling better to the foliage, spray infected plants thoroughly. Another unusual remedy for fighting fungal diseases is manure tea. This formulation fights blackspot, as well as mildew and rust, while providing foliar nutrition. Place one gallon of well-composted manure in a 5-gallon bucket and fill with water. Stir the mixture well and let sit in a warm place for three days. Strain the mixture through a cheesecloth or mesh and use the resulting tea to spray disease affected plants.
    Remember to water your rose plants at soil level and avoid getting the leaves wet. Water in the morning. Space the plants well to ensure good air circulation. Smaller rose bushes be spaced 3 feet apart and larger rose bushes be spaced 4 feet apart from one another.

    I spend hours everyday in my

    I spend hours everyday in my garden caring for plants I have raised from seeds. My plants are over-ran with powdery mildew. Especialy my peonies and ALL vines, watermelon, gourds, cantalope ect. Then there's the aphids. Every plant in the yard is covered with a disease and bugs. Also have a big problem with atleast 4 ant species. I'm really dissapointed this year. I'm happy everything grew but honestly the plants look terrible. I grow hibiscus, roses, spider plants, coneflowers, morning glorys, clematis, hot poker, iris and many more plants that attract birds and butterflys. My daylillies and grasses look terrible too... ANY suggestion?

    See the tips above and

    The Editors's picture

    See the tips above and comments from our reader for help with mildew. We have also heard that spraying a milk/water solution on the leaves will help. Use about 30% milk and 70% water. It doesn't matter what kind of milk you use.
    For the aphids see our pests page at www.almanac.com/content/aphids
    For ants you can sprinkling cinnemon or corn meal or spraying a little bit of vinegar between the plants.
     

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