White Powdery Coating on Leaves? Yup, That’s Powdery Mildew

Posted on Apr 11 2012 - 1:09am by Mike Lieberman

There is a white chalky substance on the leaves of your plants.

Your container garden looks like Pablo Escobar and his boys had a party in it…

…What happened?

Don’t worry that white powder is not cocaine, it’s powdery mildew.

You’ll notice that the powdery coating is on both sides of the leaves and will eventually start to spread.

Those leaves will eventually turn yellow and die. It can also cause the leaves to twist and turn.

Your container garden looks like Pablo Escobar and his boys had a party in it. What happened? — Tweet This

Vegetables commonly affected by powdery mildew

  • Cucumbers
  • Peas
  • Squash
  • Tomatoes

Dealing with powdery mildew

If you are first starting to plant, then one effective way to prevent powdery mildew is to allow for air circulation by pruning the leaves, especially at the bottom. This is because excess moisture is a common cause.

Once powdery mildew strikes, you can combat it with a homemade spray using baking soda and water.

There are also organic fungicidal sprays that you can use as well to help, such as Safer Brands Garden Fungicide.

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Win a Safer Brand Organic Insect & Fungicide Gift Pack

Lucky for you I am now running a contest on Facebook (through April 12, 2012) that includes the Garden Fungicide as part of a gift pack. Check it out and enter today.

Your turn

After you’ve entered the contest, in the comments below let me know which plant of yours has been affected with powdery mildew.

Image courtesy of Jeff Kubina on Flickr.

  • Robin Moehring Hayles

    Well, we apparently have this on our liriope – it’s very thick and dense by the driveway, and we’ve had a lot of rain lately, so I can see why the moisture would cause the mildew.  Thanks for the information! 

  • Tamara

    Sometimes i see it on my hydrangeas…want to be prpared for it this year..Thanks! Tamara

  • Ginger Muttschall

    Thanks for the info! This actually killed one of my tomato plants last year because I wasn’t sure what to do. :(

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    Word. My pleasure.

  • http://www.UrbanOrganicGardener.com Mike Lieberman


  • http://www.UrbanOrganicGardener.com Mike Lieberman

    That bastard!

  • Rainn

    Zuchinni. Every year.

  • Barb

    I’ve had it on my comfrey and squash.

  • http://www.UrbanOrganicGardener.com Mike Lieberman


  • http://www.UrbanOrganicGardener.com Mike Lieberman

    No bueno.

  • Jenarey

    My worst Powerdery mildew victim is my roses.  They get lovely and then the powder sets in!

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    Screw the roses. Grow some food 😉

  • Greeene2002

     i read some where that milk works ? i tried it and it smelled like sour milk in the garden – not a good smell.. Didn’t seem to work very well .. Pruning did

  • Duskshydro

    U can use honey and milk in water. Lemon juice in water. Peroxide and water 1/4 peroxide and rest water there are several safe methods

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    I’ve heard the same thing. At least skim milk is good for something.

  • http://www.UrbanOrganicGardener.com Mike Lieberman


  • http://www.facebook.com/tandy.boynton Tandy Cooke Boynton

    Nice.  I believe my gram used a vinegar and water spray for this….

  • http://www.facebook.com/tandy.boynton Tandy Cooke Boynton

    (Seems especially appropriate for the cucumbers,
    now that I think on it….)

  • Tiffany Dehart

    I had this problem on some squash, zucchini and cucumber plants I bought 2 weeks ago.  I mixed up 2/3 C water and 1/3 C white vinegar in a spray bottle and sprayed the top and bottom of each leaf and also the stalks of the plants that had the mildew spots.  They had it bad!  So far so good all of the mildew spots are gone and the plants look healthy again

  • Joanie Dorsey

    Last summer my tomatoes had it very bad. I did try the milk and water solution and it did help. This year I rotated crops and am keeping a careful eye out for it. I have been very diligent about pruning my tomatoes properly for good circulation of air.

  • onlysometimesclever

    I thought powdery mildew was caused by LOW humidity and poor circulation, not excess water.  I had powdery mildew on my red swiss chard, and it spread to some of my carrots.  All I did was prune/thin some things out, watered the leaves for several days to UP the humidity (I live in the Phoenix area), and the powdery mildew was no more.  I composted the affected leaves/tops, but ate the carrot roots no problem.  I have a smallish garden (about 6.5′ x 21′), and have now learned my lesson that it’s not necessarily the best plan to jam stuff in there as tightly as I can…  Plants need room to breathe!

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    We all need room to breathe 😉

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    Good job.

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    Good stuff.

  • http://www.UrbanOrganicGardener.com Mike Lieberman


  • http://www.facebook.com/profile.php?id=1450851488 Sandy Pqjlrxy Wilson

    My pumpkins got it this season. I also have cucumbers growing on the other side of the yard, so it’s good to know that the solution is simply baking soda & water!

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    It definitely works sometimes.

  • Amber

    I have it on a self sprouting plant in my patch. I deliberately have not pulled it out to see what it is… pumpkin or cucumber is my bet.  It has powdery mildew on it… good tip on the breathing space… it has nestled it self among the Engligh Spinach… might have to space out me thinks!

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    Word. Sounds like a plan!

  • http://mysisterspantry.wordpress.com/ Little Sis

    Thanks.  Didn’t know about the baking soda trick – a little cheaper than the store-bought spray, eh? 

  • http://www.UrbanOrganicGardener.com Mike Lieberman

    True dat.

  • http://www.facebook.com/heather.cansler Heather Archer Cansler

    The baking soda and water mix spray completely killed my cucumbers instead of just clearing the mildew!  HELP!

  • UsuallyConfused

    How about on comfrey leaves? Once they seem to mature to a certain time, they always get a chalky powder stuff on them, but I never thought it was mildew. Could it be different for comfrey leaves?

  • http://www.facebook.com/profile.php?id=100000542542712 Coco Ball

    My cabbage has been infected with some white powdery substance right under its leaves. Why is this happening and how can i prevent this? The cabbage seems to be fine its on the floor around the cabbage on the dirt. I’ve scooped up the infected dirt for and pulled off some of the leaves whats left to avoid this from happening and is the cabbage still edible? 

  • Phantz57

    My pumpkins just developed the powdery mildew but was wondering the ratio of baking soda to water?..p.s. they were organic seeds

  • http://www.facebook.com/A.J.Dove1 A.j. Dove

    How much baking soda in how much water?

  • http://www.facebook.com/GreatGrandmaNorma Norma Davis Hamby

    I just read a receipe for it. 1 tablespoon baking soda, 1 teaspoon dish soap to a gallon of water

  • http://www.facebook.com/louis.small Louis Small

    Nice info thanks. I just noticed it growing on my comfrey plants. I think I have been watering them too much. I’ll try the baking soda and water. I think it all started when I top dressed my cabbage seedlings with bone meal and blood meal, and some white substance started growing on the soil surface the next day. I think it spread to some of the other plants.

  • Tammy Jo

    We are going to try the baking soda , dish detergent and water mixture first…. but if it don’t work, I saw above something about vinegar and water what would be the diution formula on that?

  • Tammy Jo


  • http://www.facebook.com/Living4JesusAlways Michelle Mendez

    I just noticed this on my tomato plants this morning. I will try the baking soda tip too. Is it because of over watering because the leaves feel brittle a little but the soil is moist.

  • Anna

    I think I have powdery mildew on some of my pepper and tomato plants. However, we’ve been in a huge heat wave — in the 90s and even over 100, about 50-70% humidity. How can there be excess moisture in such heat? They seem to be properly pruned and have air flow. Could it be that the soil is too moist? I’ve been trying to keep them from drying out in the heat but don’t think I’ve over-watered them. Are my pots too close together? Could it be something other than powdery mildew?

  • sam

    Had it on my bonzai I started from a seed i got from an apple

  • Shannon Abbey

    You probably have blight in your soil. I think that was my issues this year. We have some new containers set up and I think the dirt was infected before hand. After your season you will need to dig up all the old roots and plants and treat your ground. Good luck!

  • Ellyn

    Is it dangerous to eat the kale if I wash the mildew off?

  • Chelseagirl …

    I’d love to know the answer to this, too.