melon vine with powdery mildew infected leaves

A Backyard Gardener’s Approach to Powdery Mildew

by | Sep 3, 2023

Welcome my friends! If you are battling powdery mildew, you aren’t alone. In fact, this year more than most, I’ve had people approach me about what to do with all the powdery mildew in their gardens! The absolute truth is that powdery mildew is nothing to fear. In fact, there is always powdery mildew in my garden in the Summer! I’m so happy to finally share allll about how I approach powdery mildew in my garden (including my favorite powdery mildew milk treatment). 

Just for fun, let’s play a little “would you rather” garden-style. What would you rather battle in the garden: powdery mildew or spider mites? Hands down powdery mildew for me!

Would you rather have blossom end rot or corn earworms? Now, THIS is a tough one. On the one hand, blossom end rot is typically temporary for me—meaning it usually is caused by a temporary, environmental issue and goes away—whereas corn earworms are really just gross and can ruin a whole crop of cobs! Surprisingly, I think I’d rather have the blossom end rot!

Overall, I think what I’m trying to say is that, on the list of things to worry about in the garden, I really hope you can start to feel a little less stressed about powdery mildew after today.

What is Powdery Mildew?

Let’s talk about powdery mildew and the different ways we can manage it in our spaces. I’ll even share a powdery mildew milk treatment that has worked surprisingly well for me!

Powdery mildew is a fungal disease that presents as a powdery white growth on the leaves of plants (see photos). It’s super common in gardens, especially where foliage growth is thick with very little air circulation. As the powdery mildew fungus grows over your whole plant, it inhibits the plant’s ability to photosynthesize—often leading to yellowing and browning leaves and die off.

closeup picture of powdery mildew on a squash plant

Here’s a closeup of powdery mildew on a squash leaf. As you can see, it looks like a white powder sitting on top of the leaf.

How to Manage & Treat Powdery Mildew in Your Garden

You probably know by now that there’s no “easy answer” in gardening. As someone who has personally fielded thousands of questions about dying plants, plant disease, and garden pests in my inbox please trust that I take no joy in telling you that there’s “many factors” and “I can’t be sure.” Sound familiar?

As with anything in the garden, there are multiple approaches you can take to manage powdery mildew in your garden. As a backyard gardener I take a multi-prong approach to powdery mildew that ranges from preventative approaches to cultural practices and organic treatments.

My Preventative Approaches to Powdery Mildew

Have you ever noticed that pests and diseases in the garden tend to manifest on the weakest plants? It turns out that stressed out plants are more susceptible to these kinds of problems. Personally, when I think back on my most stressful days, I recall how my body always seems to get sick or hurt more when I’m stressed—-it’s kind of the same idea. So, just remember that sometimes pests and disease are nature’s way of telling us something isn’t healthy or in balance. It really behooves us to simply try and keep our plants happy (with watering and adequate nutrients, etc) as the first line of defense to preventing the majority of problems.

Furthermore, proper spacing of your plants can also help keep powdery mildew at bay. When plants are crowded, the lack of air circulation —combined with warmth—-creates a cozy little environment for these fungal spores to grow! For super leafy plants that seem crowded, pruning of foliage might be necessary to improve air flow.

Grow Powdery Mildew Resistant Varieties

Another preventative route for powdery mildew is to select specific varieties that are listed as powdery mildew resistant or “PMR” on the seed listing.  These special seed types are usually F1 hybrids that have been bred and selected because of stronger resistance against this fungal disease. Be warned, crops that are listed as “PMR” resistant does not mean they won’t get powdery mildew—-it simply means that they have demonstrated a higher resistance to it in trials.

Best Practices to Tackle Powdery Mildew

Sadly, once powdery mildew sets in it’s time to move on to minimizing the damage. One thing I always like to ask myself is “how far along in the season are we?” Honestly, if it’s towards the end of the season and the crop has produced well enough, I simply remove the plant. The following paragraphs are really about controlling powdery mildew in the garden when our goal is to save the plants and give them enough time to produce some harvests.

My morning routine usually consists of pouring a cup of coffee and heading out to the garden with Pete (our pup) to do a quick walkthrough—well, I do the walkthrough and Pete does his morning business. Anyway, if the rest of the day is super packed I’ll head inside after about ten minutes and immediately sit down at the computer to answer emails, comments, and do blog updates. If I’ve got some time, I’ll take Pete inside and then head out for a slower walk to enjoy some coffee in the backyard. My point here is that it doesn’t take exorbitant amounts of time to observe your plants. Making it a habit to investigate your garden everyday can help you catch the signs of powdery mildew early. In fact, observation can help you in a myriad of ways in the garden.

butternut squash plant near the end of the season showing signs of powdery mildew

Photo from the end of August 2023. Towards the end of the season, you’ll be faced with a decision—fight the powdery mildew or let it be until it’s time to turn the garden over for the next season. In this example, my butternut squashes are almost ready to be picked! Therefore, I’m going to let them finish ripening, harvest, and then trash the plant as I clear my garden.

Removal of Infected Foliage

Once you find powdery mildew, there are a few actions you can take. Truthfully, experience is the best teacher when it comes to making these decisions. Don’t be afraid to make mistakes and know that you’ll get better with every season. Sometimes I can tell that the plant is large enough to handle the removal of the infected leaves, while other times I know it’s better to treat the plant (like with the powdery mildew milk spray I’ll share). Remember, it’s all a balance between keeping enough foliage for healthy photosynthesis and trying to stop the powdery mildew from taking over.

If you choose to remove the infected foliage, you can simply clip it off and put the debris in the trash. It’s extremely important that you don’t spread the fungal spores around your garden or in your compost. Make sure to clean up and trash any infected debris!

Powdery Mildew Milk Spray Treatment

While many resources recommend fungicides and other sprays to combat powdery mildew in the garden, I want to share what has worked wonderfully for me. Years ago I had heard about spraying a milk spray to eradicate powdery mildew. Silly me completely wrote it off because I was convinced that the milk would start to go rancid in the sun and smell terrible! Well, this year my powdery mildew problems were so bad (and a fellow Instagram gardener raved about using milk spray) that I decided to try it! Spoiler: this milk spray is now my go-to powdery mildew treatment.

Essentially, take a 50/50 mixture of milk and water in a spray bottle and generously spray the tops and undersides of the infected plant. Start this powdery mildew milk treatment in the morning, when the sun is coming out, and let the sun shine on those treated leaves! For real! Check out my YouTube video for some before and after footage.

As of now, there has been no official explanation as to why this milk spray works on powdery mildew. Some sources say that proteins in the milk interact with the sun to kill the powdery mildew. Regardless, I do have to mention that I used whole milk and it’s often reported that milk substitutes will not work the same.

before and after of powdery mildew milk treatment showing decrease in fungal spots

Curious if a powdery mildew milk treatment works? Check out the before & after on these zinnias. After the initial treatment I missed some spots, so I went back and did it again. The powdery mildew is basically gone!

My thoughts on neem oil treatment

You’ve probably heard a lot of organic gardeners rave about neem oil. Personally, I’ve used it in my garden before, but have stopped in recent years. It’s nothing against neem oil—I think it has its place in any organic gardening toolkit—but this stuff so easily burns your plants that I just don’t like the fuss! I’ve found that even when I apply neem after the sun has gone down, my plants still end up being super sensitive to the sun and have burnt. Especially since powdery mildew most often happens in the Summer for me (when the sun is intense), I just don’t reach for my neem oil that often. Furthermore, there are very specific ways you need to apply neem oil so that beneficial insects (like bees) aren’t harmed. Therefore, while neem is something I’ve used for other things, it’s just so much easier to do the powdery mildew milk treatment!

The End of Summer

It’s September already, and I can see a change in the garden setting in. Despite the fact that the days are still hot, the mornings officially have a chill in the air—this is how Fall rolls in here in Southern California. You can see the garden looking more bedraggled, and I’m already assessing what plants are far gone and will be removed for my Fall seedlings. Moreover, the battle with powdery mildew for this season is coming to an end. As I said, this late in the season I tend not to fret over powdery mildew— I will let any remaining fruit ripen on the plant and simply pull the whole thing out for the season.

Truthfully, it feels so good to get all these words out on paper. There have been so many times I’ve been asked about powdery mildew, and it’s been a dream of mine to have a full blogpost that covers all the nuances of this topic to refer to. If anything, I hope this post has helped you feel more comfortable with powdery mildew. It’s truly one of the most common garden diseases that we all battle—we got this!

Plant a California native shade garden

1 Comment

  1. Stacy

    Hi Randi, thank you for this post and this wonderful website. It brings a lot of inspiration to me as a novice homeowner and gardener. When deadheading my Iceberg roses, I noticed rose rust infecting many leaves. Do you think this milk treatment can help combat it? Have you dealt with rose rust before? I will appreciate any advice on what I should do. I am in South Mission Viejo and we have experienced moist mornings and kind of ocean breezes since moving in a couple of weeks ago.


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Meet Randi

Urban gardening is my jam. I’m Randi, California girl who obsessively gardens to grow food and flowers around my urban home. Seasonal, simple living is what inspires me~ I hope it will inspire you too. Join me in crafting a life and home connected to the garden Read More>>>>

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