Near the end of summer, nights begin to cool, the sun isn’t as intense, and it is finally time to harvest your garden. These changes can also bring an unwanted guest: powdery mildew. Most gardeners have seen it and may not know what it is. It looks like someone sprinkled powdered sugar all over your plants, but it’s actually a fungal infection.
Powdery mildew has microscopic spores that spread easily and can weaken plants and reduce their fruit production, the exact opposite of what you want happening in your garden. There are many species of fungi that cause powdery mildew infections, and most are specific to one type of plant. For instance, while apples and grapes can both be infected, the fungus species is unique to each and will not spread from one type of plant to the other.
The plants that seem to suffer the most are in the squash family: zucchinis, crooknecks, pumpkins, and butternuts.
Now we’ve identified what it is, let’s talk about how it grows. Like most fungi, powdery mildew grows best in humid and cool areas with stagnant air, which is why we often see it in the fall. The most effective weapon you have in preventing mildew is controlling when and how you water your garden.
Watering just before the sun comes up is a great way to ensure your plants will have the water they need for the day and that any water that gets on the leaves will evaporate when the sun comes up. Remember, this fungus likes moisture, so letting the leaves and soil dry each day will reduce the likelihood of infection.
Let’s discuss how to water. While sprinklers are great because they can water a large area, they also deposit water onto leaves, which makes them a bad choice for gardens. A drip irrigation system is the clear winner. Install a line exactly where you want it, set a time to water in the morning, and you’re done.
Even with a drip irrigation system in place, powdery mildew can still show up when weather conditions are just right. Now what do you do? You have two choices: prune the infected leaves away or apply a chemical to kill or slow the growth of the powdery mildew.
Pruning is a great place to start because it increases air flow. With a few tools, you can clean up your garden and give your plants a fighting chance and give you more produce. You’ll need a pair of pruning shears, rubbing alcohol, a cloth rag, and a bucket.
Each pumpkin leaf has a long petiole, the leaf stem that attaches to the main stem as seen in the picture below:
Using clean pruning shears, cut the petiole away from the main stem. Dab your cloth with rubbing alcohol and wipe the blades of the shears clean between each cut. Discard infected leaves in a bucket. Do not compost infected leaves. The spores can overwinter and will infect next year’s crop. You can either throw the leaves away or burn them. If most of the leaves on a plant are infected, pruning them all is not an option. In this case, prune the oldest leaves and leave the younger ones in place and prepare a treatment.
There are many chemicals you can apply to kill powdery mildew. Most home improvement stores have a shelf full of fungicides, but if you prefer to have chemical residue in your garden, never fear, because there are alternatives.
Believe it or not, milk is one of the best homemade treatments you can use. Fill a spray bottle with a 1-part milk and 10-parts water. Shake well and spray on both sides of the leaves in the morning and let the sun do the rest. Diluted milk has been used by homesteaders for generations to treat powdery mildew and is safe and non-toxic for plants and animals.
Now that you know what powdery mildew is and how to prevent it and treat it, you can keep your garden healthy and producing all season long. Happy gardening!