Best Ready-to-Use Copper Fungicide for Tomato Blight in Organic Gardens

By Lena Moss | Sustainable Garden Enthusiast

If you’ve ever grown tomatoes—especially organically—you know the heartbreak of watching healthy plants suddenly droop, blacken, or spot up with blight. It’s frustrating, even for seasoned growers, but it doesn’t have to be the end of your crop yield.

As someone who tends to tiny patio tomatoes, raised beds, and vermicompost bins like they’re part of the family, I’ve seen (and tried) just about every natural fix for tomato diseases. And when it comes to fast, effective, and organic-friendly solutions for tomato blight, one product consistently rises to the top.

Let’s dive into why Bonide Captain Jack’s Ready-to-Use Copper Fungicide is the best ready-made spray you can get your hands on for controlling blight and protecting your tomato harvest—organically.

What Is Tomato Blight and Why Should You Care?

Tomato blight is a general term, but it usually refers to two main types:

• Early Blight: Caused by the fungus Alternaria solani
• Late Blight: Caused by the oomycete Phytophthora infestans

Both are devastating, especially in warm, humid climates. You’ll notice:

• Brown or black spots on leaves
• Wilting and yellowing foliage
• Dark lesions on stems or fruit

Without fast action, your entire tomato crop (and nearby plants!) can quickly fall victim. If you’re growing organically, your options are limited—but powerful. One of the most respected tools? Copper fungicide.

Why Copper Fungicide Works So Well on Blight

Copper-based fungicides have been used in agriculture for generations. They work by disrupting the enzymes that fungal and bacterial cells rely on, essentially stopping reproduction and spread.

According to the University of Minnesota Extension, copper fungicide sprays are one of the most effective organically approved methods for controlling early and late blight on tomatoes.

Why I Recommend Bonide Captain Jack’s Copper Fungicide (Ready-to-Use)

After years of mixing concentrates, checking ratios, and occasionally burning plants (oops), I switched to Captain Jack’s Copper Fungicide for one main reason—it’s easy.

Here’s what makes it stand out:

• Ready-to-use—No measuring, no mess. Just grab the bottle and spray.
• OMRI-listed—It’s USDA-certified organic, so you can use it without violating organic gardening rules.
• Battles both fungus and bacteria—Ideal for other plant issues too, like powdery mildew or bacterial leaf spot.
• Gentle enough for regular use when applied according to the directions.

How to Use It for Tomato Blight

Using Bonide’s ready-to-use copper fungicide couldn’t be more straightforward:

1. Start spraying as soon as you see the first signs of blight or every 7–10 days as a preventative.
2. Spray in the early morning or late evening—never in direct midday sun to avoid leaf burn.
3. Ensure even coverage on leaves (top and underside) and stems.
4. Reapply after rain as the protective layer can wash off.

Pro tip: Always follow the label. Even organic treatments can cause harm if misused.

What Gardeners Are Saying

I’m not the only one shouting this fungicide’s praises.

Many reviewers on Amazon mention:

• “This stopped powdery mildew in its tracks.”
• “Works wonders on tomato blight—I’ve saved three plants so far.”
• “Love the ready-to-use spray bottle, especially for quick spot treatments.”

Most negative feedback? Some gardeners experienced leaf spotting or burn—usually after applying during full sun or too frequently. Again, stick to the directions, and your plants will thank you.

The Eco Side of Copper: What You Need to Know

Because copper doesn’t easily break down in soil, repeated use can build up copper levels, potentially harming beneficial soil microbes.

So, like all good things, moderation is key.

Use only when needed and consider rotating with biological fungicides like Bacillus subtilis (Serenade) during routine maintenance.

Still, when you’re mid-season, and your tomatoes are under siege, the effectiveness of copper-based sprays like Bonide’s can’t be beat.

Use Case Spotlight: My Battle Against Blight

Last summer, my patio heirloom tomatoes were thriving—until one week of rain and humidity brought on a swift blight takeover. Within a few days, four plants were half-yellowed and drooping like sad umbrellas.

Enter: Captain Jack’s Copper Spray.

I trimmed the damaged leaves, sprayed the remaining healthy growth, and set reminders to avoid sunny-hour applications. The result? Nearly all the plants bounced back, and I still got a lush crop by fall.

That’s the kind of product I stand behind.

Copper Fungicide vs Concentrates vs Bio-Fungicides

Feature	Captain Jack’s RTU Spray	Concentrated Copper Fungicide	Biofungicide (e.g., Serenade)
Ease of Use	⭐⭐⭐⭐⭐	⭐⭐	⭐⭐⭐⭐
Organic Certification	✅ OMRI	✅ OMRI	✅ OMRI
	✅	✅	❌ (Mainly fungi)
Ready-to-Use	✅	❌	✅ (some)
Ideal User		Experienced growers	Green-focused gardeners
Price Range	Moderate	Cheaper per oz	Moderate to High

In short: If you want the easiest and most convenient way to treat both fungal and bacterial blight, Captain Jack’s is the way to go.

When to NOT Use Copper Fungicide

I love this stuff, but even the best tools need a full toolbox. Here’s when to seek an alternative:

• Soil health is a concern—Rotate in biofungicides between copper applications.
• Plant is severely wilted or too far gone—Remove infected plant and disinfect tools to avoid spreading.
• Temps are above 85°F—Risk of phytotoxicity increases. Always spray during cooler hours.

Organic doesn’t mean worry-free—so be thoughtful and balanced.

Why Organic Growers Should Still Consider Copper Fungicides

If you’re like me, you care deeply about what goes into (and out of) your garden. We compost, companion plant, and avoid unnecessary chemicals.

But organic gardening isn’t about suffering through preventable diseases—it’s about being intentional. And copper, when used judiciously, is one of the most powerful disease-prevention tools we have.

As an OMRI-listed product, Bonide’s formula is approved for USDA organic growing. So you can protect your plants while honoring your sustainable values.

Final Thoughts: Is Captain Jack’s Copper RTU Worth It?

For me, growing food is personal. It’s about learning through losses and celebrating every lush tomato and juicy cucumber. It’s also about being efficient—because plants (and people) don’t always wait for ideal conditions.

That’s why I keep a bottle of Bonide Captain Jack’s Ready-to-Use Copper Fungicide right on my garden cart.

Whether you’re brand new to organic gardening or nursing your hundredth tomato plant back to health—this is the kind of tool that makes plant care less frustrating and more fruitful.

Ready to Save Your Tomatoes From Blight?

If you’ve been hunting for the best organic-friendly fungicide that’s easy to apply, combats both fungus and bacteria, and is made for home gardeners—you’ve just found it. Stop blight before it starts (or catch it before it spreads) with this gardener-approved favorite.

Don’t wait until your plants are beyond help. Give your garden the protection it deserves.

Happy growing, and remember—a well-loved tomato plant will always give back more than it takes. 🌿

– Lena Moss, Organic Garden Enthusiast