Powdery Mildew

How to Identify and Control Powdery Mildew

Powdery Mildew2
Photo by Pollinator: Wikimedia Commons

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Wondering about that white fungus on your plants? The fungal disease powdery mildew affects a wide variety of plants and takes away a plant’s nutrients. This causes the plant to bloom less and become weaker.

What is Powdery Mildew?

There are many different species of the fungal disease powdery mildew, and each species attacks a range of different plants. Unlike many other fungal diseases, powdery mildew thrives in warm, 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. That being said, it is capable of infecting your plants under a wide variety of conditions.

When the fungus begins to take over one of your plants, the mildew that forms is made up of many spores. These spores carry the infection to other plants through the wind. Powdery mildew can slow down the growth of your plant. In some cases, if the infection is severe enough, powdery mildew can kill your plants. 

    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 Control Powdery Mildew 

    • Remove all the infected plant parts and destroy them. Remember, do not compost any infected plant, as the disease can still be spread by the wind and persist in the composted materials.
    • Spray infected plants with fungicides. Effective organic fungicides for treating powdery mildew include sulfur, lime-sulfur, neem oil, and potassium bicarbonate.

    Prevent Powdery Mildew

    • Choose plants that are resistant or tolerant to powdery mildew. Many mildew-resistant varieties of cucurbits (melons, cucumbers, squash, etc.) have been developed and can be bought from major seed suppliers.
    • Avoid watering plants from overhead in order to reduce relative humidity.
    • Selectively prune overcrowded areas to increase air circulation; this also helps to reduce humidity around your plants.
    • Spray your plants with the fungicides mentioned above according to the directions included with the products.
    • 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.

    Reader Comments

    Leave a Comment

    White power on leaves

    I have white powdery substance on my zinnias. Will this make the seeds in the flowers be bad for next year?

    Yes, the mother plant has

    Yes, the mother plant has been infected and will pass along those genetics to the seedlings which will also carry the disease.

    powdery mildew on bee balm

    the info I have is to spray with milk/water mix or baking soda/water mix...I am doing that , but is it a one time treatment or multiple treatments?......please advise how many times and how often to spray,,,ty

    Powdery Mildew Treatment

    It will likely require multiple treatments to keep the fungus at bay. Test the mixture on one plant first, waiting at least 24 hours to be sure that there are no negative effects. Then spray all affected plants at least once a week. After three or four applications, wait to see if symptoms return before spraying again.

    White powder fungus

    I have been fighting this in my house for almost 4 years. I have tossed out so many plants I can’t tell you how much money its cost. I am wondering if two giant chinese evergreens are causing it - the have never had it at least not visibly. I am ready to torch the house or at least throw away every plant I have and fumigate / steam clean every nook and cranny including AC ducts. I am at my wits end.

    White powdery mildew hay spread to much cherry tree

    I'm just sick, I just got 2 new cherry trees 1 Bing, 1 Black Tartarian cherry tree and I spread hay down first before I mulched around the bottom of the trees. The hay I used has white powdery looking stuff in the middle of it, not knowing I put it down and put mulch on top of it. It is Nov 13th here in Wisconsin and cold out. Does the hay have white powdery mildew and will this now infest the trees next spring? Should I dig up all of the mulch and get rid of it all? What should I do?

    Powdery mildew

    I have powdery mildew on my peonies. I sprayed with neem oil but now the plants look dry and damaged. Should I cut the plants all the way down? Will they come back next year if I do? Is there anything I can add to the soil? This is the second year this has happened to these plants. Last year I did not treat them with anything.

    How to keep mildew of peonies plant

    Every year after the season I start getting fungus on my peonies what can I use to prevent this.

    PM on peonies

    Are your peonies crowded? You might try thinning them out, per above to improve circulation: Selectively prune overcrowded areas to increase air circulation; this also helps to reduce humidity around your plants.

    You could also try the spray solution listed above:

    • 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.

    Powdery mildew

    You mention to destroy plants and not compost. What method is best? Will burning cause the mildew spread to other plant? How about other diseases on plants, will burning spread disease?

    Burning powdery mildew

    Did you ever find if powdery mildew is spread by burning infected plants?

    Burning Powdery Mildew

    I have been doing a lot of research on powdery mildew. Temperatures above 90 degrees kill it.

    Grape Vine

    Our concord grape vine seems to have "expired", after 5 years of fairly reliable fruity growth. How can I tell if I need to start over, or find some "life" in what remains? Sad. The neighboring vines are doing well.

    Rosebush fungus ?

    Would like to know what some white fuzzy looking stuff on the rosebuds might be and
    what can be done to eliminate it.
    Looks like the fuzz n peaches but is a bright white in colour

    powdery mildew on roses

    It sounds like powdery mildew. See guidance above and

    • plant roses in full sunlight.

    • space plants to allow ample air circulation

    • fertilize to maintain vigor but do not overfertilize

    • avoid wetting leaves when watering; use drip irrigation, if possible

    • prune affected canes and collect and destroy cuttings (do not compost)

    • use fungicide with care

    • in future, select rose varieties that are resistant

    Powdery Mildew and Environmental parameter

    Would like know about relationship between disease powdery mildew and environmental factors specifically Temperature, Relative Humidity, Rain Fall and Wind speed. Is there any quantitative MODEL which defines relationship amongs them in control of disease.

    Red Spider Mite on hydrangeas

    Can you tell me what to spray to rid the plant from this pest. It has spread to other plants in the area.

    Red Spider Mite on Hydrangea

    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 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

    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

    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

    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,

    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!

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