When gardeners find white spots on the leaves of their zucchini plants, no one can blame them for assuming the plants have powdery mildew, a very common fungal disease that looks like a white powder was sprinkled over the plants. But white spots are naturally occurring in the patterns on zucchini leaves, so there is likely no cause for alarm. In this video, I show you how to tell the difference between powdery mildew and white spots that are simply a part of the leaf pattern.
The quick and straightforward way to test a spot is to rub it with your finger. Powdery mildew spores will come off the leaf with gentle rubbing, while white spots that are part of the leaf pattern will be unaffected. It’s as easy as that.
If you do find powdery mildew on your plants, wash your hands and your tools before touching another plant, to cut down on the disease’s spread.
Plants severely affected by powdery mildew appear generously coated in white power. To prevent mildew, plant zucchini in full sun and provide adequate spacing so air can circulate among the leaves. Avoid watering from overhead, which creates an environment that is ripe for fungal spores to take hold. Instead, apply water underneath leaves, possibly with a drip irrigation system or soaker hoses, right at the soil level. Read my comprehensive guide Powdery Mildew Prevention & Control for more tips.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Organic Vegetable Gardening: My new premium online course membership opens in 2023. Sign up for the waitlist here.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, AeroGarden, Milorganite, Soil3, Greenhouse Megastore, PittMoss, Territorial Seed Company, Earth’s Ally, National Wildlife Federation and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.