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Powdery Mildew

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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
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. Mix 1 TBsp each of baking soda and horticultural oil (dormant oil spray)or a few drops of liquid soap to 1 gallon of water. Spray weekly making a new mix each time. 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.
You can 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 things 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.

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7 Comments on Powdery Mildew»

  1. 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.

    Comment by jennifer — 2/2/2006 @ 3:03 pm

  2. 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.

    Comment by Tara — 3/15/2006 @ 5:44 pm

  3. 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.

    Comment by tamara — 7/25/2006 @ 11:42 am

  4. 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.

    Comment by susan chase — 8/25/2006 @ 9:48 pm

  5. 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.

    Comment by Elizabeth Leaird — 7/9/2007 @ 5:31 pm

  6. 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

    Comment by Emily — 9/5/2007 @ 6:49 am

  7. 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.

    Comment by Keri — 5/11/2008 @ 6:02 pm

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