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Powdery Mildew

Powdery Mildew starts out as whitish spots that spread quickly until the entire leaf is covered. The white powdery growth is a fungus that with time becomes gray to tan/brown felt like patches. Leaves may become stunted, curled, chlorotic and eventually wither and dry up. Mildew occurs from hot days , high humidity ,cool nights and at the change of season.

powdery mildew on grape leaves powdery mildew on zinnia

Fungicide recipes

Depending on the severity, spraying it with a baking soda formula is effective as a preventative when applied regularily.  For active infections spray daily for a week. 

1. Mix 1 TBsp each of  baking soda  and horticultural oil (dormant oil/vegetable oil) or a few drops of liquid soap to 1 gallon of water.  Spray weekly making a new mix each time.  It will not elliminate the disease but help control it.

2. Mix 1 tsp baking soda with a few drops of vegetable oil in 1 quart of water. Spray or paint on the leaves.  Works on houseplants, cucurbits & roses (balck spot).

Another suggestion is  a solution of 1/3 milk and 2/3 water and spray on plants. Use every other day.

I also heard of mixing 1 tbsp of pine sol to 1 gal of water as a mildew spray.  Neem Oil is also affectective in controling infections. Use 1 oz.(2 Tbsp) of Neem oil and 1/ 1/2 tsp of dishwashing detergent to one gallon of water. Spray once a week for two weeks.
Use chemical sprays such as Benomyl (systemic fungicide), sulfur/fungicidal soap early in the growing season as a preventative or as soon as symptoms appear. A synthetic fungicide Baylaton sold as Strike also works well on mildew. Always follow label directions, to make sure the product is approved for specific plants. The combination of Neem and baking soda is the safest control method. Once the disease takes hold, it is difficult to control.

Some cultural preventatives  that can be done are to remove the infected leaves, do not crowd the plants, provide good air circulation and keep plants well watered and stress free. Grow resistant plants when available.

  1. powdery leaves on my rosemary plant I received a rosemary plant for Christmas and it seemed to be...

12 comments to Powdery Mildew

  • jennifer

    my son started plant in school 2nd week in aug. we live in florida. but now his leaves are little brown on some and white spots. what is causeing that.we havent really been cold it is a good size plant but no pumkins yet. it has like 10 buds on it but they die what should we do?

    White spots on pumpkins can be powdery mildew a fungal disease that can occur with fluctuating temperatures and both humid and dry weather. Try spraying it with a fungicide containing chlorothalonil at 7 day interval. Some varieties are resistant to powdery mildew.

  • Tara

    Hello, I’m new to this forum, and have been searching for information on what I am experiencing with my jasmine plant. It is indoors, with lots of light, in a cold climate. It has developped a mold on all it’s leaves. It is white and powdery. Any suggestions? Also, when we water it, the water runs straight through, we were told not to soak it, but I feel like it’s not even getting a moderate watering. Thanks

    Sounds like you have powdery mildew on your leaves. It is a airborne fungus that thrives under certain environmental conditions-cool nights, high humidity. See the article on powdery mildew for treatment-baking soda or Neem Oil. I wouldn’t worry about the watering, it is better to have good drainage than roots sitting in water. The plants require less water in the winter.

  • tamara

    we seem to have white powdery mildew on our soil. it started in 1 or 2 plants in winter and has spread to our entire household collection. i can only find information about powdery mildew on leaves, not one of our leaves are effected, is this the same thing? will the same treatment be sufficient? will repotting in new soil and cleaning out pots also help? i appreciate your info.

    It isn’t powdery mildew but a similar fungus that is in the soil. A too wet soil surface is an ideal environment for a fungus as well as fungus gnats. A recommended remedy to try is 1 Tbsp. of baking soda to 1 gal of water, drench the soil and let the water drain out of the bottom. Let the soil surface dry before watering again.

  • susan chase

    While away, mildew has taken over my peonies and a lilac tree. It is too late to prevent. Is there a treatment? Will the mildew effect the health of the plants for the next growing season? Can they survive this?!?

    It’s too late to prevent. To control it you can use a baking soda spray (look under powdery mildew article). At this time of the season mildew is more of an aesthetic problem, the plants have done most of their growing and are winding down for the year. Mildew will not affect next years growth but some plants are more suseptible to it than others so when you see signs of powdery mildew start spraying.

  • Elizabeth Leaird

    My squash plants have white powdery mildew, which has begun to spread to my zucchini and cucumbers. I went to Lowe’s to purchase a treatment for the mildew. I was advised by two garden center employees to use Disease Control, which is manufactured by Bayer Advanced. The active ingredient is Tebuconazole (2.9%). We sprayed the plants last night and checked on them this morning. The white powdery mildew did not seem to be affected by the fungicide. So, I called Bayer’s 1-800 question line. The woman informed me that this product is not to be applied to plants used for food. She could not give me any further information. The Poison Control Hotline and the National Pesticide Information Center could not offer any additional information either. If you have any information concerning this fungicide, please share. I am heartbroken at the thought of having to destroy my garden that I have worked so hard on.

  • Emily

    Crepe myrtle
    I just bought a “dynamite” crape myrtle tree. It’s leaves are all black. When I asked the person at the nursery about the black leaves, she said it had previously had powdery mildew, but it had been treated and it “should” be okay. The price had been reduced and she said the black would rub off and that by next spring(again), it “should” be okay. Is this true? And also will it spread to my other plant shrubs and trees?

    There are two diseases in question here. One is powdery mildew-which is prevalent in Crepe Myrtle and sooty mold. Sooty mold is the result of sap sucking insect infestation such as aphids, scale, mealybugs, & whitefly. These insects secrete a sticky substance called honeydew which is a perfect medium for a black powdery fungus called sooty mold. It is more an unsightly problem but will not harm the plant. The black mold covering the leaves will reduce photosynthesis. You can wash it off but its not necessary. It will not spread to other plants unless you have sap-sucking insects and honeydew on the leaves. Your “dynamite” has superior mildew resistance and is a good choice to grow. For more info

  • Keri

    There is a powdery white substance on the stems of my plants (mostly succulents). It started with one houseplant and now it’s spread to some of my other houseplants. What is this and how can I get rid of it?

    Most likely it is powerdy mildew. When the weather warms up set your plants outside with good air circulation and spray with baking soda mix (1TBS baking soda to 1 QT H2O +drop of detergent). For more info see above article.

  • Carl Wheeler

    In south Florida I have a large hibiscus tree that is covered with the white fungus and is in bad shape. I have been used an oil fungicide, but no luck. Any help, thanks, Carl

    HI Carl
    See the above article for other recommended treatments for powdery mildew. It’s hard to control in a humid environment. If it doesn’t look like powdery mildew then you might have mealy bugs which also like to attack hibiscus.

  • Amethyst

    Do you have an eco-friendly solution, you know, no chemicals, to Powdery mildew? i have creek full of frogs in my back yard, and chemicals clog their pores and kill them.

    Hi Amethyst
    Try the baking soda remedy mentioned in the above article.

  • Sarah

    Hi,
    I have 3 hibiscus that I thought were experiencing some sort of mildew/mold due to the heat here in Houston TX. After further research, it appears it may be mealy bugs as the blooms never open but instead shrivel up, all new growth is very dark green and bunched up almost like small heads of lettuce and there is a white coating on the branches along with a black ashy substance. Is there any hope for these plants- it has been about 5 months of trying different solutions and I am about to rip them out so the rest of my bushes and shrubs are not affected… We are now trying to sell the house and I want to make it appear as attractive in the front as it is inside and this is not helping!!! Thanks!

    Hi Sarah
    Hibiscus is susceptible to pink hibiscus mealy bug which will cause distorted bunched up new growth. Mealy bug is difficult to eradicate. The best recommendation outdoors is to use a biological control with Lady bugs. Insecticidal soap and horticultural oil can be affective in reducing populations. You can also try using a systemic insecticide, which will kill all insects (good and bad) but will provide some control. If infestation is severe, you might considered replacing the hibiscus. http://etipm.tamu.edu/insect_alerts/ph_mealybug.cfm

  • Donna Setterholm

    I have the worst case of powdery mildew through out my gardens. I am planning to mow the perennial beds to about 3.5 inches and burn the clippings. Then I will spray with a milk solution. My pumpkins and squash leaves are white with it. Are the pumpkins and squash safe to harvest and eat? I have not put any chemicals on the plants, yet.

    Hi Donna
    Your pumpkins and squash should be safe to eat as long as you haven’t sprayed any chemicals. If there is any powdery mildew on the surface of your vegetables, scrub it off before eating. Powdery mildew occurs late in the growing season and doesn’t necessarily come back next year unless conditions are right. Some years its worse than others.

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