How to Prevent Pests and Diseases

The best way to control pests and diseases? Grow healthy tomato plants. Just like humans, weak and stressed plants catch illnesses.

What Healthy Plants Need

• Enough sunshine
• Good soil
• Right amount of water
• Fertilizer
• Good variety selection
• Proper planting time
• Sulfur dust (for fungus prevention)

Young plants start healthy. As they grow and set tomatoes, disease targets them. The goal is to harvest a great crop before disease gets them. Usually, we're successful.

The Fungus Problem

Probably the most common tomato problem is fungus. 80-90% of growers get some form of fungus on their leaves and think it's normal—or that the plant needs more water or fertilizer. There are hundreds of different kinds of fungus. Leaves dry up, turn brown, yellow, spotted, die and fall off. Most of this is powdery mildew.

Once fungus is on the leaves, it reproduces and spreads through spores—tiny microscopic bodies floating in the air that land on your plants. The spores spread by wind and water to new leaves and other plants. Leaves are food factories for tomato plants. Less leaves = less energy = less tomatoes and more stress.

How to Stop Fungus

Use sulfur dust. It prevents fungus from reproducing. Sulfur dust works and it's organic—it comes from Mother Nature. Apply a light coating when you see early signs of discolored leaves low on the plant.

Look at the photo above. The three plants on the right have been treated with a light coating of sulfur dust. The plant on the far left was never treated. Notice the difference? The treated plants show early fungus signs down low—time for another light coating.

When to Stop Treating

Once a tomato plant has reproduced (set fruit and seeds), it naturally reduces the fight against pests and disease. When a plant reaches its peak and nears the end of producing, I stop worrying about pests and diseases and get ready to pull it out and plant a new one.

Remember: a tomato plant's goal in life is to reproduce, then it dies.

Why I Don't Use Pesticides

Tomato plant disease and pests are everywhere—in the soil, in the air, on your hands, on your tools. If something's going around, the tomato plant will probably get it.

When possible, buy disease-resistant tomato plants. The label will indicate if that variety is disease resistant. Remember: resistant to a disease, not immune from it.

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Next Steps

Master the fundamentals of healthy plants →
Learn proper feeding techniques →
See disease-resistant varieties →

You're welcome to share this information with others—family, friends, garden clubs. Sharing tips helps everyone grow better.

Dave Freed / The Tomato Guy