Powdery mildew on your plants seems like a rite of passage as a gardener. The fungus causes the leaves to become a rainbow of colors of yellow, white, and brown. Eventually, many of the leaves die. My squash, pumpkins, and cucumbers are infected with powdery mildew every year. So instead of fighting it, I am proactive in preventing it. Here’s how.
What is Powdery Mildew?
According to Colorado State Extension
“Powdery mildews produce mycelium (fungal threads) that grow only on the surface of the plant. They never invade the tissues themselves. The fungi feed by sending haustoria, or root-like structures, into the epidermal (top) cells of the plant. The fungi overwinter on plant debris as cleistothecia or mycelium. In the spring, the cleistothecia produce spores that are moved to susceptible host tissue by splashing raindrops, wind or insects.”
The fungi is host specific, meaning that powdery mildew on grapes won’t affect your squashes.
In order for the fungi to thrive, the following contribute to the situation:
- Overcrowded plants where there isn’t enough air movement
- Dry humid conditions. (NJ’s August.) 60 to 80 degree weather is the perfect storm. Believe it or not, powdery mildew won’t grow in temperatures in the 90’s.
- Plants in shade are more susceptible to powdery mildew.
Best Course of Action:
Prevention is key. Having experienced powdery mildew every year of gardening, this year I started to proactively treat it.
Generally, I wait until the mildew appears, and then I start treating it with Serenade or Neem. Honestly, it stops the spread of powdery mildew but you will lose many leaves in the battle.
So what do I use?
Yep. Milk. My formula is 30% organic milk and 70% water. I use to use a 10:1 ratio of water to milk but my gardening mentor, Barbara Pleasant uses my new formula.
Powdery Mildew Spray with Milk:
Several studies have shown that using milk or whey have been as effective as sulfur based mildicides. In 1998,Wagner Bettiol, a researcher in Brazil found that various dilutions of fresh cow’s milk controlled powdery mildew in greenhouse grown zucchinis.
Based upon Bettiol’s research, Peter Crisp of the University of Adelaide, Australia, decided to try milk dilution on grapes to curb powdery. He states:
“In the presence of sunlight, milk and whey, for instance, appear to foster the production of biologically damaging free radicals, such as hydrogen peroxide and superoxide radical.”
He used a 10:1 water to milk solution and found it was helpful at keeping powdery mildew at bay for roses as well.
It is very important that you wet both sides of the leaves AND you spray when it is sunny and hot. I typically spray around 2 PM in the afternoon. I will admit spraying both sides of the leaf is hard.
It doesn’t matter if you use non-fat, whole, or skim milk.
When to Spray:
I spray once a week starting in the beginning of June. My plants start climbing my trellises at this point. If you get powdery mildew, powdery mildew spray with milk spray will not get rid of the fungus. You will need to use a fungicide of some sort like a DIY formula using baking soda or Serenade.
Join the Conversation:
How do you prevent powdery mildew?
Photo of powdery mildew by Jeff Kubina
Disclaimer: There may be affiliate links in the post. By clicking the link, you will not pay more for the product. It helps to keep Green Talk going.