Battling Mid-Summer Fungal Diseases: Your Essential Garden Guide
When Fungal Diseases Crash the Summer Garden Party
You step outside, morning coffee (or evening cocktail) in hand, ready for a breath of fresh air and a peek at your thriving garden, and suddenly your cucumbers look like they’ve been dusted in powdered sugar! That telltale white fuzz? A classic sign of powdery mildew, one of the most common (and most annoying) fungal diseases gardeners face. This year, unusually rainy weather has upped the ante, turning many mid-summer gardens into prime real estate for all sorts of fungi. But there’s good news: with the right approach, you can prevent and control these diseases while keeping your garden healthy and productive.
Powdery Mildew, Leaf Spots, and Blights—Oh My!
Fungal diseases manifest in several ways:
Powdery mildew: Looks like a white powder on leaves, thriving in warm, humid conditions with poor airflow.
Leaf spot diseases (like Septoria): Present as black, brown, or yellow spots. These often lead to premature leaf drop.
Blights (like tomato or potato blight): The most serious culprits, capable of wiping out entire plants in just days.
These fungi love:
Wet, crowded leaves with limited airflow
Plants over-fertilized with nitrogen (which produces tender, fungus-attracting growth)
Debris left from last season, which can harbor spores waiting to strike again
In especially wet years, gardeners may face higher-than-normal outbreaks as plants can’t dry out between rainstorms.
Prevention and Organic Treatment Options
Changing the pH, Boosting Airflow, and Home Brews
Milk Sprays: Simple and effective, a 10% solution of milk (1 part milk to 9 parts water) applied weekly can change the leaf surface pH and, courtesy of proteins that react with sunlight, fry fungus spores on contact. Use whole milk and spray in the morning for best results.
Baking Soda Solutions: Also raises the pH of the leaf surface but use with care: overuse in hot weather can burn leaves. Test on a small section first and spray early in the morning.
Neem Oil: Works for both fungal and pest problems but can cause leaf burn if applied in strong sun or excess. Again, use early in the day before the sun is strongest.
Organic Fungicides: Sulfur and copper-based sprays are OMRI-approved and provide powerful preemptive coverage, though heavy rain can wash them away. Rotate your treatments (milk, copper, potassium bicarbonate, etc.) to prevent resistance.
Bonus: I use First Saturday Lime, a non-water-soluble lime product that changes surface pH and holds up better in rainy conditions.
Prune, Space, and Stake for Success
Pruning: Regularly prune lower leaves, especially on tomatoes, squash, and cucumbers, to improve airflow and reduce soil splash-back (which spreads spores). I’m not usually a heavy pruner, but for disease prevention I generally remove the lower 12 inches of leaves off my tomatoes, and as needed with my squash and cucumbers.
Staking and Trellising: Lifting plants off the ground with supports or trellises drastically improves air circulation and keeps fruit from contacting wet soil or mulch.
Proper Spacing: Avoid overcrowding. Even if you interplant to maximize space, your plants need room to breathe, particularly in wet or humid years. There’s no shame in thinning out overcrowded beds mid-season to boost airflow.
Water Smarter: Water early in the day and always at soil level. Never routinely wet the foliage, unless you’re washing off dust on a sunny day. Drip irrigation or soaker hoses are ideal for keeping leaves dry while delivering moisture to the roots. Use mulch to prevent soil splash but remember even mulch can stay soggy after frequent rain (which is why trellising helps!).
Sanitation and Record-Keeping: Your Secret Weapons
Remove Diseased Material Promptly: Avoid leaving any diseased leaves or plants in the garden. Dispose of them completely instead of composting.
Sanitize Tools: Fungal spores hitchhike on pruners and garden gloves, so give everything a good wipe-down between uses.
Garden Journals and Calendars: You know I love a good garden journal. Note every outbreak and treatment. Set preemptive reminders as part of your yearly garden planning. Prevention is always easier than scrambling to fix an outbreak!
Don’t let powdery mildew, leaf spots, or blight catch you off guard or ruin your season. With the right organic treatments, smart plant care, and a dash of vigilance, you can keep your garden healthy even in the wettest years. Remember: start early, rotate treatments, prune for airflow, and practice good sanitation—and you’ll be back to sipping that coffee surrounded by gorgeous, productive plants in no time.
Need more help? Episode 261 How to Tackle Mid-Summer Fungal Diseases has all the details!
Your Friend in the Garden,
Karin