The Garden

Powdery mildew and how to deal with it

Powdery mildew and how to deal with it

If you have ever had a garden then you have probably encountered the evil that is powdery mildew. I comes in quick and takes hold, but licking it doesn’t mean the end of your gardening ventures. So read on to find out more about it and if you are just here for the into on how to prevent and treat it feel free to scroll on down to the bottom.

Disclosure: Some of the links below are affiliate links, meaning, at no additional cost to you, I will earn a commission if you click through and make a purchase.

Powdery mildew is something that must be dealt with pretty much every year, but this year it was really bad in my garden. This was for a multitude of reasons, which I touch on below. So if you are trying to prevent it or already up to your ears in it, read on to find some hints and tips on what you can do.

What is powdery mildew?

Powdery mildew is (primarily) a follicular fungal disease that is caused by members of the Erysiphacae family. It is one of the most common and easily identifiable diseases you will find in your garden. It can appear out of nowhere and take over in as little as 7-10 days, so vigilance is key. It tends to take hold after the plants have set their fruit. Luckily, it is easy to identify which is good as it means once you know you have it, then you can do something about it. Once it is established it tends to look as if someone has sprinkled flour all over the leaves of your beloved squash. In it’s earlier stages it looks like slight yellow discolourations that spread over the leaf surface.

Early stages of powdery mildew on a squash plant

What plants are affected by powdery mildew?

Powdery mildew LOVES members of the cucurbits family but it can affect over 10,000 types of plants. Outside of the cucurbits it has an affection for onions, strawberries, tomatoes, apples, pears and many others. I had it on my cucurbits, tomatoes and peonies this year, this horrible beastie really isn’t too picky. The right strain will even attack your lawn!

How does powdery mildew occur?

Powdery mildew tends to rear it’s ugly head in mid-summer, or at least it does in my neck of the woods (I am in zone 5B in Ontario, Canada). Powered mildew does tend to start in the south and make it’s way north as the temperatures increase. It usually shows up when the temperatures hit 20-27C (68-80F) and the humidity is in the 50-90% range. Powdery mildew reproduces both sexually and asexually via spores which are then spread from plant to plant by the wind. It can travel hundreds of miles which seriously sucks. Powdery mildew can also be spread but sucking insects such as woolly aphids

Will powdery mildew kill my plants?

I feel the need to state up front that powdery mildew is not an instant death sentence for your plants. That is it isn’t going to do them a lick of good either, so we need to get it under control ASAP. It will cause leaves to die off and it can stunt your plants as well. As the spores form on the leaves they reduce the plants ability to make sugars. This can cause the fruit produced on plants with powdery mildew to be less tasty. I have found cucurbits are a bit more resilient as long as they have roots along their vines. Not only does their vining nature allows them to grow away from the site of infection but they can be more resilient due to the extra rooting.

Powdery mildew on tomatoes

Is powdery mildew harmful to humans or pets?

Powdery mildew while super fugly can’t infect you and it won’t harm you if you touch it. Your plants on the other hand won’t be as lucky. You can even still eat fruit from plants that have powdery mildew. But chances are they may not be as good as they usual are. The skin of the fruit can in some cases be affected by the powdered mildew and they can have some extra lumps or bumps. That said they won’t hurt you if you eat them, you may just be a bit underwhelmed.

I wouldn’t suggest eating any greens affected with powdery mildew because ewww and also I saw mention that it can cause allergic reaction in some people. So maybe take a pass on those.

Is powdery mildew systemic?

I hadn’t asked myself this question before, and then the other day a friend was over and we were discussing powdery mildew and he asked me if I thought it was systemic or not. So I stared at him blankly and said more research (on my part) was needed. Which brings us here, to me including it on their lengthy powdery mildew post.

So what have I learned? Well, primarily I learned two things

  1. The debate about systemic vs non-systemic seems to rage most among those who grow cannabis.
  2. Nobody has proven it 100% either way

Team systemic seems to believe that powdery mildew once introduced spreads via the plants vascular system and that it is there IN the plants? So why does this matter so much? Well, if you consider that most cannabis plants are propagated by cloning you can see how this would be a big deal. Team non-systemic believes that powdery mildew is essentially topical but arguable very hard to get rid of.

So what do I think? Well after an evening of googling, and not having delved into any scientific papers (which I love but I’m just really tired tonight) I am aligning myself with Team non-systemic. Most information I have come across leads me to believe it is topical, one article I was reading mentioned the roots were not affected. One would believe that if it was vascular that it would be present in the roots. That said this was only cursory investigation on my part and if anyone reading this has any links to scientific papers please leave me a comment below cause now I’m curious.

Can it live in the soil?

Powdery mildew does tend to overwinter in the soil, especially if there is left over plant debris from the previous years garden. It is always a good idea to properly clean out your garden and to take care NOT to compost any infected plant material.

Is it contagious to other plants?

There are MANY species of fungus that cause powdery mildew and most a plant specific. This means that having powdery mildew on your peonies does not guarantee that it will jump to another plant that tends to be susceptible to powdery mildew. It is more likely that with the right conditions multiple species are active and each looking for their chosen host plant.

How to prevent and treat powdery mildew

8 Things you can do to treat and prevent powdery mildew, so that it doesn’t crush your garden dreams!

So I am going to split this list into two sections, firstly those thing that you can do to prevent powdery mildew. Then secondly, what you can do when it shows up and tries to crush your garden dreams.

How to prevent powdery mildew

#1 – Plant in full sun

For things like tomatoes and cucurbits this is a win-win situation. They crave 6-10 hours of direct sunlight so there isn’t really a negative to this one in my opinion.

#2 – Provide good air circulation

If I had to pick just one of these 7 to recommend it would be this one. Space is key in preventing and controlling the spread of powdery mildew in my opinion. There are many ways to accomplish this. First, give plants their recommended space wether you are doing “normal” gardening in the ground or square foot gardening (which I LOVE) pay attention to the spacing suggestions. I found that a great way to grow squash this year was vertically on my arched cattle panel trellises. If you want to know how to build them, you can check out my YouTube video on the whole installation process.

Another option for vertical growing, is to train your squash or tomatoes up a string. It is also a good idea to trim and leaves under the fruit as well. When it comes to zucchini I only grow them in pots now so that I can space them out better without losing a huge amount of space in my raised beds. Powdery mildew will appear in a snap if you neglect to provide good air circulation. Plus it makes it easier for it to spread if the next leaf is right there, touching the infected leaf.

Powdery mildew on a pumpkin leaf

#3 – Be aware

This was my biggest failure this year, which is an even more painful failure for me as I LOVE DATA! I am usually very aware of my surroundings and patterns and people…I notice a lot. But this year the garden got away from me a bit as I was spread too thin with The Day Job, a bigger garden, outside commitments and coping with The Hubby’s bipolar. What this means is that powdery mildew was able to take hold and get established in my garden, before I even knew it was there.

You should always be present and aware in your garden. Looking at your plants and examining leaves and under leaves is the best way for you to stay on top of issues, whether they be in the form of pests or diseases.

#4 – Plant resistant varieties

Because I am an heirloom snob this isn’t an option for me which sucks because heirlooms seem to be more susceptible to everything. But that wont stop me from pretty much growing them exclusively. You can check out 5 reasons you should grow heirlooms plant here. But if you are not an heirloom snob, then planting powdery mildew resistant varieties is a great option! That said, that doesn’t mean you skip these other helpful hints and tips. They are resistant not immune!

#5 – Keep pests at bay

As I mentioned powdery mildew can be spread by sucking insects such as wooly aphids. So you are going to want to make your garden less attractive to them so they go wreak havoc in someone else’s garden. Companion planting is a great way of doing this along with attracting beneficial aphid eating insects such as lady bugs to your garden

How to treat powdery mildew

#6 – Remove any affected leaves

Once it is in your garden you need to take action quickly to reduce or at least slow down he spread. The first piece of business is to remove and affect leaves.


Sorry, I don’t mean to yell but I can’t reinforce this enough! The spores can overwinter in the soil and the last thing you want to do is to introduce them into the compost you worked to hard to create! If you aren’t already making your own compost or if you are but it smells like you are hiding dead bodies then you may want to check out my post on how to compost like a pro.

So once you have removed any infected leaves and put them in the garbage we can move on to the next step. Oh and if you see it on perennial plants like I did on my peony then go ahead and cut them right back. Especially if it is after they are down blooming for the season.


Powdery mildew on a peony

#7 – Apply a follicular spray

Once you have cleaned out as many infected leaves as possible you will need to apply a follicular spray. You can either buy a pre-made one from the store such as Safer’s 3-in-1 garden spray or you can make up your own DIY concoction.

Some DIY powdery mildew treatments

  • Potassium bicarbonate
  • Neem oil
  • Milk solution
  • Sodium bicarbonate

My reader has up to this point on the subject if the best DIY treatment for powdery mildew, seems to indicate that ehe milk solution seems to yield the best solution. That said, nobody seems to be able to agree on the dilution ratios! I have seen 10:1, 9:1, 6:4 and 2:1 with water always being the larger amount. But seriously….that is some HUGE variation in ratios! So my best suggestion is to start on the more dilute range of the spectrum (10 parts water to 1 part milk) and slowly increase if you don’t think it is working.

I opted to try the baking soda approach which I paired with my go-to DIY garden oil, neem oil. You do have to be careful when using neem oil on your plants. You don’t want to apply it in full sun as it can burn the leaves. Plus you have to be very careful not to spray near any flowers as it is POWERFUL and could hurt beneficial insects. I use it in my DIY insecticide and it is powerful stuff.

My DIY Baking Powder Soltion

  • 2 cups Water
  • 1/8 tsp Neem oil
  • 1/8 tsp Dish soap
  • 1/2 tsp Baking Soda

#8 – Reduce fertilizer application

Powdery mildew tends to affect newer leaves so we don’t want to be jacking our plants up into high leaf production. Because in this case it’s going to be counter productive, especially if you are using a nitrogen based fertilizer which promotes leaf growth. We want to provide extra nutrients to our plants to help them live their best lives without making too many leaves. It’s a balancing act for sure.

That’s it folks! I hope that was helpful and the you are able to keep powdery mildew at bay in your garden.

Follow me on Instagram & YouTube for more micro homesteading adventures

No Comments

    Leave a Reply