Keeping your tomatoes healthy is one of the most rewarding challenges for a gardener. By learning to spot the symptoms of three common ailments early, you can save your plants before the damage spreads.
Early Blight
Early Blight, caused by the fungus Alternaria solani, usually appears on lower leaves as dark, circular spots with concentric rings, often resembling a target. It thrives in warm, humid weather (between 75°F and 85°F). To manage it, practice good airflow by pruning the lower 12 inches of foliage and mulching heavily to prevent soil-borne spores from splashing onto leaves during rain.
Late Blight
Unlike early blight, Late Blight (Phytophthora infestans) is a fast-moving, devastating disease that can kill a plant in days. Watch for water-soaked, greenish-gray patches on leaves that quickly turn brown and papery. It prefers cool, damp conditions (50°F to 75°F). If you identify late blight, remove the infected plants immediately and bag them—do not compost them—to prevent further contamination.
Pro Tip: Always water at the base of the plant rather than overhead to keep leaves dry, which significantly reduces the risk of fungal pathogens taking hold.
Blossom-End Rot
Blossom-End Rot is not a disease, but a physiological disorder caused by a calcium deficiency in the fruit. You will notice a dark, sunken, leathery patch on the bottom of the tomato. It is often triggered by inconsistent watering, which prevents the plant from transporting calcium to the developing fruit.
- Maintain steady soil moisture by using drip irrigation or a soaker hose.
- Avoid over-fertilizing with high-nitrogen products early in the season, as this encourages leaf growth over fruit health.
- Add compost to your soil to improve structure and moisture retention.
By monitoring your garden closely and maintaining consistent watering habits, you can stop these common issues from ruining your summer harvest.