Combating Powdery Mildew and Other Summer Diseases
Dear friend,
July has arrived in all its lush glory, draping the Blue Ridge Mountains in green and letting the long days unfold like a warm embrace. The garden is alive—truly alive. Zinnias are strutting their colors like fireworks, cucumbers are swelling under broad leaves, and tomato vines are reaching ever higher, eager to show off their first blushing fruits.
But amid all that vibrancy, tucked in the warmth and humidity of early summer, lurk the quiet threats every Southern gardener comes to know: fungal diseases. They sneak in with the dew, ride the wind with the spores, and wait patiently for those moments when the garden’s defenses are down.
And so, just when we’re marveling at how lush everything looks, we might spot it—that telltale dusting of gray-white on a leaf. Or the strange yellow spotting on a basil plant that looked fine yesterday.
Let’s talk about the most common culprit this time of year: powdery mildew.
If you’ve grown squash, cucumbers, zinnias, or bee balm (monarda), you’ve likely met this uninvited guest. At first, it shows up like a little sprinkle of flour on the leaf surface. Not alarming, just a light dusting. But left unchecked, it can spread quickly—covering entire leaves, slowing photosynthesis, and weakening the plant’s overall health.
I remember one year in particular—hot, sticky July afternoons followed by cool, damp nights. By mid-month, my zinnias were covered in mildew. I’d planted them close, wanting that lush, cottage-garden look, but the crowding reduced airflow, and the fungus took full advantage. It was a learning moment, the kind that teaches more than a book ever could.
Air circulation, I’ve learned, is half the battle.
Spacing your plants properly might feel like restraint in the spring when everything’s small, but by midsummer, you’ll be glad you gave them room to breathe. Good airflow allows leaves to dry quickly, denying fungal spores the damp habitat they crave. I try to stake my tomatoes early and trellis my cucumbers, even if they’re in a raised bed. Lifting the vines keeps them dry and makes harvesting easier to boot.
I also make a point to water at the base of the plant, using drip irrigation or a watering wand that lets me reach in low. Overhead watering may look romantic in the golden morning light, but it’s a fast track to mildew, especially if it happens late in the day.
And here’s something I do regularly during these humid stretches: I water early in the morning. That way, any splashed water that does end up on leaves can dry quickly with the sun. If the garden is damp going into nightfall, it becomes a welcome mat for fungi.
Still, even with our best efforts, mildew sometimes shows up.
When it does, I reach for my go-to baking soda spray. It’s simple:
1 tablespoon baking soda
1 teaspoon liquid dish soap
1 gallon of water
Mix it up and spray it on affected leaves in the early morning or evening (never during the heat of day). The baking soda changes the pH on the leaf surface, making it less hospitable for fungal growth.
If you prefer a ready-made product, there are plenty of organic fungicides—like neem oil, potassium bicarbonate, or sulfur-based sprays—that can help slow the spread. Just make sure to read the label and avoid spraying when pollinators are active.
But powdery mildew isn’t the only challenge we face in these humid July weeks.
There’s also downy mildew, especially on basil. It looks a little different—yellow patches on top of the leaf, and a fuzzy gray or purple underside. It spreads quickly, particularly in warm, humid weather, and once it’s taken hold, it’s hard to control.
I’ve found that growing resistant varieties, like ‘Eleonora’ or even Thai basil, gives you a head start. The flavor is slightly different, but the resistance is worth it. I also try to grow my basil in containers or raised beds with plenty of sun and airflow, pruning early and often to keep the plants bushy and well-ventilated.
Then there’s the dreaded tomato blight, especially late blight, which is every bit as devastating as its reputation suggests.
You’ll know it by the dark, water-soaked spots on leaves and stems, followed by rotting fruit. It’s disheartening to watch a tomato plant go from lush and promising to blackened and collapsed in a matter of days. And once blight is in the bed, it can linger in the soil for years.
That’s why crop rotation is so important. I try not to plant tomatoes or other nightshades (peppers, eggplant, potatoes) in the same spot more than once every three years. It’s a challenge in a small space, but even a little distance can help.
With tomatoes, I also remove the lower leaves as the plant grows, especially if they’re touching the soil. That reduces the chance of spores splashing up from the ground during rain or watering. Mulching with straw or wood chips also helps minimize that splash zone.
When I do need to prune or remove diseased material, I disinfect my pruners with a bit of alcohol or bleach solution between plants. It might feel tedious, but it can make the difference between one infected plant and five.
Sometimes, though, despite our best efforts, a disease takes hold.
I remember one summer when the cucumber vines were thriving one week and ghostly white the next. I tried everything—baking soda sprays, pruning, spacing—but it was too late. The mildew had won. So I pulled them. It felt like giving up, but in hindsight, it saved the neighboring squash and watermelon.
That’s the balance we learn over time—knowing when to fight, and when to let go.
Because here’s the thing: no garden is ever perfect. There will be spots on leaves, bug holes in petals, and sometimes a whole row of something that simply doesn’t make it. But that doesn’t mean we’ve failed. It just means we’re gardening in the real world, alongside nature, not apart from it.
Fungal spores are everywhere—on the wind, in the soil, in the rain. We can’t eliminate them, but we can create conditions that tip the balance in our favor:
Proper spacing and pruning
Watering at soil level
Mulching to reduce splash
Choosing disease-resistant varieties
Practicing crop rotation
Applying organic treatments as needed
And maybe just as importantly, we can change our expectations. A leaf with a bit of mildew isn’t a catastrophe. A tomato with a soft spot isn’t a tragedy.
In fact, I’d argue that a healthy garden isn’t one where everything is flawless—it’s one where the gardener knows how to respond. Knows when to wait, when to intervene, and when to cut back and try again.
So if you’re out there this July, checking on your squash or admiring your zinnias, and you spot a bit of powdery fuzz—don’t panic. Take a breath, make a plan, and remember: you’re not alone in this. We’re all learning, one leaf at a time.
Here’s wishing you a vibrant summer garden, full of life, color, and resilience. May your zinnias bloom boldly, your basil stay fragrant, and your tomatoes ripen to perfection—spots or not.
Stay cool, and keep growing,
Logan
P.S. If your garden is struggling with mildew or other summer stressors, we’re here to help. Visit Unicorn Farm Nursery & Landscaping to schedule a consultation. Together, we’ll get your garden back on track—beautiful, bountiful, and buzzing with life.