Why Leaves Get White Spots: Powdery Mildew

Plant leaves getting white spots? There's a good chance that's powdery mildew, a fungal disease of plant foliage and stems. It is particularly common is susceptible plants, such as cucumber, squash, melons, roses, grapes, phlox, monarda and some broadleaf trees (like the horse chestnut from the opening shot). In this video, I'll discuss the conditions that favor this infection of leaves, as well as ways to prevent it. If you want to treat without heavy chemical fungicide, I have a couple of recommendations at the end of the segment.
If you find these videos useful, there are a few little things you can do to help me out:
Have a look at our Amazon shop: www.amazon.com/shop/fraserval...
Follow our farm on Instagram: / fraservalleyrosefarm
Like us on Facebook: / fraservalleyrosefarm
Or better yet, subscribe to this KZbin channel: kzbin.info...
And for a place to indulge in random garden anarchy: / unrulyrosesociety
Photo credits:
An assortment of the public domain PM pictures were taken by Scot Nelson. Thanks Scot!
Maple by Jerzy Opioła, (CC BY-SA 4.0)
Variegata di Bologna by T. Kiya, (CC BY-SA 2.0)

[@jeangough8053]

Your always so informative and helpful I think I can stop panicking now when I see it! Thank you 🙂

[@MarthinB75]

Thanks for another informative video, Jason. Enjoy your content, as you never try and push/sell specific products. But you always explain garden ailments and provide treatments/solutions. Always a pleasure watching and learning form you.

[@FraserValleyRoseFarm]

Thanks Marthin. I appreciate the feedback

[@carmenbailey1560]

Great to know and yes I have phlox that have been effected with powdery mildew. Going to give this a try, thanks for sharing 👍❤️😊

[@pamd1861]

Thank you for the great info

[@gardencookeat22]

Ive learned a lot! Thank you

[@xiomaramartinez3212]

Great time for learning!! Thanks for share this amazing information!!!

[@FraserValleyRoseFarm]

My pleasure. Thanks for watching

[@irisrichards7070]

Thank you. Excellent advise. Kind regards

[@camus83489]

best youtube vidoe on powdery mildew - thanks

[@melfuz]

Perfect timing! This is the first year I've seen powdery mildew on my roses (I just started planting flowers two years ago) and had no idea what it was. I bought some spray from a garden centre and it seems to work fairly well, but it isn't totally gone. This is great information..now I know much more about PM than I ever expected I would 😉 Thank you!

[@FraserValleyRoseFarm]

Thanks Melanie. Glad to help!

[@long5454]

))ll)llll)ll)lll))llllllll)ll)lllllllllllllll))lll)))llllll)llllllllllll

[@douglashoule9666]

good info, thanks

[@user-fd3wl1pr7s]

It is in the rainwater, if you look closely it is worse where there is pooling of water in a leaf. You can do your own experiment, and rinse everything after a rainfall. Rinse with filtered water or even tap water. and you will see the powdery mildew will be eliminated. Also in greenhouses or polytunnels you are fine as well

[@ashvinravi1297]

Thank you... It really helped😊

[@jenniewilliamsmural]

Thank you Jason - you are truly wonderful. I'm getting the horticulural oil and potassium bicarb on Amazon. Warmest regards Jennie

[@janetcorey5102]

Thank you so much. Your advice is so clear and not overwhelming

[@fatamabegum4436]

Thanks very helpful video!

[@IAmJustAPerson-]

This is good to know thank you and I am a New Plant lover so i have a Parade Roses

[@caysnow2]

I have powdery mildew on my heirloom dahlias. We are coastal, with fog, cool temps and high humidity. All three! I've been using neem oil, soap and water but will add in the baking soda. Thank you!

[@FraserValleyRoseFarm]

Thanks Cay. Good luck with your dahlias

[@susanl9635]

Thank you for the info! Recently planted a hedge of icecap roses which were supposed to be more disease resistant than iceberg roses but had the worst case of powdery mildew after unusual heavy rains this spring. Ended up pruning out a lot but some keep coming back and I’m still battling with it. Will have to try the potassium bicarbonate mixture.

[@FraserValleyRoseFarm]

Best luck Susan. I hope you'll find them more resistant in coming years when their roots are more established.

[@michellesundara8392]

thank you so much!!!

[@jennielunn2226]

Thank you from NZ. My potted souvenir de la malmaison has powdery mildew. It is on a north facing veranda (all day sun) so as it doesn’t get wet and ball. I shall prune and spray very soon 🌹

[@FraserValleyRoseFarm]

Hi Jennie - those Bourbon roses! I love them, but they're pretty susceptible to PM in my experience. Best luck with Souv. and I hope it recovers well.

[@frankbeckworth9302]

Sincere thanks for another terrific video, and a timely one too! I observed powdery mildew on two Altissimo roses at the start of July. The local hardware store recommended a product containing Bacillus subtilus. I'd be interested to know your opinion of using that to get rid of powdery mildew. In my experience thus far it hasn't worked at all, so I will try one of your mixes ... probably not the milk, though, as my wife is quite sensitive to odors! I am embarrassed to admit I never would have guessed that powdery mildew on roses might be caused by under-watering. I've been careful to prune them for good air circulation, and both have put on great growth and an abundance of beautiful flowers throughout the summer. Thank you again, Jason, for your informative video.

[@FraserValleyRoseFarm]

Thank you Frank. Bacillus subtilis works decently as a preventive on a wide range of fungal pathogens, but I haven't had any success with it as a curative.

[@yonokzeller5402]

Thanks again👍🏽🙏🥰

[@deborahfromdcspetersoncity9213]

Very good video Jason and informative solutions to the powdery mildew problem. Keep up the great work.

[@kishoredamaraju1404]

I also have powdery mildew on my moong dal. thank you for sharing.🌱🌱🌱🌱☹️🥰🥰🥰🥰

[@janetcorey5102]

Great info and as usual clear and concise. One ? Would you start spraying vegetable leaves early as a preventative? Thank you

[@FraserValleyRoseFarm]

It may be worth it for cukes, squash and melons.

[@ella11ella63]

Thank you 😊

[@simonelafontaine5985]

So useful, thank you so much for this! Just a few days ago I saw this on the flower buds on one of my potted roses (a Chica Kordana in pink). I have never seen it before. I have increased watering, but should I remove the infected flower buds?

[@FraserValleyRoseFarm]

Only if it's severe. Most roses can bloom right through a little touch of PM

[@wangfeng175]

Thank you！

[@moniquegreene4867]

Thanks for this, incredibly helpful. My old rambler rose (transplanted) got a bad case of powdery mildew last year, and definitely under-watering didn’t help. I’m in NZ so in winter now. My question is, do I need to prune all of the shoots off and start again, or can I just prune for shape? Just conscious that your pruning video recommends pruning off diseased branches, so was wondering if powdery mildew leaves qualified as a disease for pruning

[@FraserValleyRoseFarm]

I'd remove stems that are visibly covered with the active mildew unless that's more than you think the plant can handle. But if the stems aren't actively infected, just prune for structure and maybe give treat with lime/sulfur & dormant oil to clean up excess remaining spores.

[@alejandrabarrios7072]

Hello, thank you very much for sharing your knowledge. I bought 2 months ago 2 David Austin Roses is my first time with them but now they are sick with powder mildew because it has been raining a lot. A few days ago I put water mixed with milk as a fungicide but it was terrible, the leaves are now yellow, wrinkled and the buds do not open, yesterday I saw them with mold on the entire plant. I do not know what to do....

[@FraserValleyRoseFarm]

My pleasure. So from your description, you have three related issues: 1) Newly establishing roses, 2) Powdery Mildew and 3) the milk spray. Newly planted roses often stress in their first season. Combined with wet weather, it's no surprising that the roses would be stricken with PM. The mildew symptoms include the white spots, twisted foliage, and in severe cases, yellowing, defoliation and flower abortion. Neither milk nor baking soda spray is an effective curative - that is, they're better to prevent infection. The way I'm reading it, the roses are still badly infected with PM. The milk spray could be contributing to an ugly "moldy" look on the leaves, but is probably not the cause of yellowing, twisted foliage or flower loss. At this point, I'd advise patience. Try to reduce stress in the plant. If it's hot, make sure the roses are getting enough water. You can remove some of the worst infected of the plant leaves or badly infected stems.

[@lynnmoule8417]

Hi my new young shoots on roses are coming through with powdery mildew what should I do please

[@sldulin]

Jason- I'm always scanning the background to see if you have any daylillies, but I never see any? So I do have a number of them, I am in the same climate zone as you and i am at a loss as to what to do about daylilly gall midges. A short video on that from the internet's best explainer would be nice!

[@FraserValleyRoseFarm]

I do have a few in my front garden - thanks, I'll add the topic to my list

[@sheilatrant-mccarthy2727]

didnt know what neem oil was but know a lot of gardeners recommend it, found out its banned in England and has limited use in canada, it cant be used commercially.i was surprised considering it is a `vegetable` oil, so ill have to use the horticultural oil and soda suggestion

[@anitaswart.]

I have bought neem oil and neem cake powder in the UK at : the naturalgardener.co.uk. I am very lazy to spray, but put about a handful of the powder at the roots of my roses and watered it in well. Think I did it in the spring and now again and for the first time in years I have got no mildew or black spot and look very healthy. Penelope is a fantastic rose and flowers it's socks off. Good luck

[@sunflowerarts5]

Thanks one of my Rose got white powdery mildew ...

[@tracikellogg4946]

Love your videos! My question is about the black spot on roses spray. You mentioned canola or horticulture oil. Is the horticulture oil Neem Oil?

[@FraserValleyRoseFarm]

Hi Traci. Horticultural oil is a very light oil (I think petroleum based) that is relatively gentle on the foliage of the plants. Even vegetable oils can be fairly hard on plant tissues.

[@tracikellogg4946]

Thank you very much!

[@audigutierrez6946]

Hi Jason, I totally forgot to ask this on your previous video, but how do you overwinter your propagated lavender? I saw that you put in them in small pots, do you just leave them in their 4 inch pots outside??

[@FraserValleyRoseFarm]

Hi Audi. I have the unheated greenhouses, so that's where I'll be overwintering them - yes, in the 4 inch size.

[@walterbrooks5141]

Idk anything about roses. I want to learn more. My bush has the powdery mildew on the leaves, I think. But in addition the stems aren't green or just brown. They are like brown and white strips. 😢

[@ella11ella63]

Hi there, how often do you spray the plants with the potassium bicarbonate and oil mixture to treat the plants and/or to prevent mildew ? Thank you 😊

[@FraserValleyRoseFarm]

Every 2 to 3 weeks is the problem persists.

[@just-saying]

Thank you for your video on powdery mildew. My question relates to something slightly different. My zinnia leaves are being eaten by something. I can't identify by what. This happens mainly at night. Something the skeleton of the leaves is there but the soft tissue is chewed away. I tried pretty much everything. I sprayed with solution of baking soda, soap and neem oil, even tried to add garlic, mint and paprika. This problem is also present with dahlia. Please help.

[@FraserValleyRoseFarm]

There's loads of pest that will chew zinnia and dahlia leaves. The night-time feeding makes me think of slugs/snails. Earwigs are also a possibility.

[@janetang5327]

I've seen it on Erithyrina sandwicensis

[@Tweety2U2]

🌷🌹thank you!

[@proletariatsgarden]

Because I spray my roses regularly, they mildew situation was not that bad through the years. But this year really makes different, as the rainy season came to soon (so I can’t spray to prevent), and my neighbour got a big shrub rose in her yard, and left for vacation for about 2 months, neglected her rose. I saw some mildew built up on her rose, but it’s a huge one, so it doesn’t affect it too much, but I think the wind carries the pores and contaminated mine, plus the weather … I am having a headache dealing with it. I alternate spray my roses with different chemicals every other day, as long as it’s not raining. But still, they bounce back really quick. I want to use sulphur powder this time, but I’m in an endless lockdown in the city and no logistics are available. 😭😭😭 The mildew did impact on the flowering this years, with less flowers and more ‘dead’ buds. It’s so annoying.

[@FraserValleyRoseFarm]

Sorry to hear you're still in lockdown. That must make for all sorts of challenges!

[@paulbraga4460]

i would have expected a deeper answer than this. powdery mildew is a nutritional problem, as is most plant pest and disease...blessings

[@FraserValleyRoseFarm]

Hi Paul. I'm always encouraged when I hear a grower looking at a problem through a different lens. Nutrient management is one reasonable approach to pests and disease, but certainly not the only one. In the case of PM, I could find some studies on attempts to control by reduction of N (like this one: link.springer.com/chapter/10.1007/978-94-009-0585-6_91) with inconclusive results. Another approach was to supplement with potassium silicate and MKP (on squash). Those results showed promise, but I'd reserve judgement a bit because the study wasn't specific to roses. In any case, the video I made was a 10 minute overview of the subject. I prioritized describing the symptoms and pathogen, the conditions it thrives in, some of the cultural controls and remedies. I hope you'll also understand that even when I post a 10 minute video, the average view-time is closer to 4 minutes. A video that goes into reviewing the literature on nutrients is perhaps beyond the attention-span (or even usefulness) of my typical viewer. On the bright side, KZbin offers essentially unlimited bandwidth, and I say this with pure intentions: if you feel there's demand for a deeper (or different) dive into the topic, there's nothing stopping you from uploading your own take on it.

[@paulbraga4460]

@@FraserValleyRoseFarm well, i didn't expect such a kind reply, unlike from a soil scientist who said outright that soil nutrition has nothing to do with. will into the research you appended here...mygreathanks and blessings sir.

[@GardenDoodles]

We stopped planting zucchini because of powdery mildew which then started to show up on our salvia plants and nearly killed them.

[@FraserValleyRoseFarm]

Thanks Garden Doodles - though I maybe should add one note: there are quite a few different pathogens that fit under the "powdery mildew" umbrella, and not all of them can spread from one species of plant to another. So even if you have (for instance) grapes which are pretty susceptible, that may not make them a threat to spread PM to other plants in your garden.

[@GardenDoodles]

Fraser Valley Rose Farm Thanks for the clarification. Good to know.

[@katm.1124]

Can you please help me. I have a crabapple tree and the leaves are dropping like crazy. Theyre yellow with black spot... and the leaves fall into my flower bed. I bought 2 new rose bushes and they both got the fungus and I had to pick off their leaves and now they're bare and im afraid they're going to die. My question is... can the same fungus on the crabapple Travel to my roses? Please help is appreciated!!! The roses are called Wild Blue Yonder and Sedona. Ive used the Bonide Rose x 3 in 1 and Neem oil. But i couldn't save the leaves. And the wild blue yonder is supposed to bloom again, but i had to clip it all the way to the ground. Im so mad. :( if I know for certain that its the same fungus as the crabapple, then I can rule out other things.

[@heatherstephens9295]

Check out hydrogen peroxide 3% diluted then followed about a week later with baking soda 😊

[@FraserValleyRoseFarm]

Hi Kat. I think it's more likely apple scab on the crabapple. Different pathogen. I couldn't find anything to indicate that either disease could transfer across from apple to rose or vice versa.

[@buddyplatt6496]

Hey there, my climbing rose needs help. I don't have 'white' spots on my leaves, but rather, tiny speckled 'brown' or 'cream' colored spots on my leaves. I have no idea what my rose is dealing with. Help me please.

[@FraserValleyRoseFarm]

Have a look on Google to see if your problem matched the pictures of rust on rose leaves.

[@N0N4M30]

Hey Jason I did deadhead my freshly new planted roses 6 weeks ago (I bought 6 different ones) and only 2 of the plants are flowering again , even though I followed all the instructions 😭 what did I do wrong or what can I do now? I fertilize them once a week but except for those 2 rose plants nothing is flowering (the 4 other rose plants ) I’m devastated

[@FraserValleyRoseFarm]

A little patience. Newly planted roses can take a while to establish. It wouldn't surprise me to see a delay between flowering.

[@N0N4M30]

Fraser Valley Rose Farm thank you ! When should I stop fertilizing?

[@meirgi91]

Hi i got a question...it may not relate with th video hahaha... so i do a regular spray of fungicide to avoid any fungal infection on my roses... So i drench the whole plant up and below the leafs... after it dries, the leaf will have some powdery residue left.. normally i just leave it.. But i begin to wonder if the leafs are coverd witht the funcide residue will it decreases photosynthesis? or block the plant to breath or any kind of blockage or growth issue?

[@FraserValleyRoseFarm]

The spray residue would have to be on pretty thick to cause any real problem fro photosynthesis or transpiration. I think you're probably fine to leave it.

[@meirgi91]

@@FraserValleyRoseFarm thank you for your reply appreciate it.. May i request if u dont mind do an episode on ideal soil temperature for roses... I live in Malaysia the tropics... i alwys get paranoid with my soil temperature.. i understand that fertilizer give an impact in soil heat and also compost... so ive reduce tht. But im not sure why i still do feel the soil is relly hot to touch. im just afraid id be killing the microbes in the soil.. Today at 2pm ive chcek temperature at one of my soil i found tht it was 41.2 Celcius.....

[@mwoods4608]

What about house plants?

[@FraserValleyRoseFarm]

Yes, powder mildew can happen inside as well

[@hasmukhpatel7972]

Thanks

[@karensingleton5935]

Is it recommended that washing the vegetables leaves in dish detergent (small amount) once fungus is on them you can still cook them?

[@GumriRN]

My Rose leaves don’t look like powdery mildew, I don’t think it is; there’s no patching at all. So, can anyone reading this, tell me, if you wipe powdery mildew off with a finger? Russ suddenly appeared the day AFTER a very hot dry day at 95° one day, & 60° the next, I noticed all the leaves 🍃 had what looks like, ashes were dropped on them with No Patches at all. The ash-like residue is evenly distributed & hardly visible. Also, the white almost microscopic flecks are only on the outer sides of leaves, not underside at all. Any IDEAS 💡 ANYONE? I could actually blow this white stuff off!

[@FraserValleyRoseFarm]

The lack of "patchiness" and other symptoms of PM (yellowing, twisty leaves) - plus the fact that you describe it as very evenly distributed, it kind of sounds like some kind of ash or dust. But can you find any on surrounding plants or surfaces?

[@GumriRN]

@@FraserValleyRoseFarm-I’m going to check the broadleaf herbs I’ve planted next to this Rose. It’s so weird tho’. I carefully inspect that plant so thoroughly every day. Every neighbor passing by, marvels at its prolific beauty & scent. I’m certain, this dust was not there 2 days ago. Let’s see today what happens. I may try the milk treatment in spite of the unpleasant odor. This Rose’s scent will overpower even smelly old milk.

[@GumriRN]

@@FraserValleyRoseFarm -After thunderstorms last night whatever that white particulate substance was, it’s now totally gone. The leaves are as green & pristine as ever. Thank goodness. Still, I do wonder what it was. Reminded me as I think about it, like the pollen sometimes seen on car Windows. Weird.

[@FraserValleyRoseFarm]

Good to hear!

[@jloveskitkats]

I thought it was butterfly eggs.😂😂

[@davidmichael3189]

I am so fed up with Rose leaf diseases I pulled all the poxy bloody things off leaving piss poor frames only and I'll never buy Roses again wish I'd just bought flipping Strawberries.

[@FraserValleyRoseFarm]

Sorry to hear you struggled with it David. If you ever think to try again (like, way in the future, when your current disappointment is less fresh) maybe look at the Kordes variety 'South Africa' or 'Beverly' - they're much cleaner than the average rose, and gorgeous too.

[@kishoredamaraju1404]

My own moong dal is ruined ☹️☹️☹️☹️☹️☹️☹️☹️☹️😭😭😭😭

[@FraserValleyRoseFarm]

So sorry to hear it!