CORVALLIS, Ore. — Knowing the hows and whys of tomato diseases gives gardeners a leg up when it comes to growing one of the garden’s most treasured vegetables.
Brooke Edmunds, horticulturist with Oregon State University Extension Service, offers tips for recognizing and managing common tomato problems throughout the growing season.
Blossom drop
Often caused by dry soil and dry winds, but may also result from a sudden cold spell, heavy rain or excessive nitrogen. Usually, not all blossoms will fall off — another set of flowers often follows.
Blossom-end rot
The end of the fruit farthest from the stem turns brown or black. This is caused by inconsistent watering and calcium deficiency and is most common in western Oregon. Water deeply and regularly. To improve calcium levels, apply lime to the soil in the fall for next year’s crop. Learn more in Extension's guide on blossom-end rot.
Leaf roll
A physiological issue typically caused by heavy pruning or root injury. Some cultivars naturally exhibit leaf rolling. Plants may lose leaves but generally recover. Learn more in Extension’s guide on leaf roll.
Sunscald
Green tomatoes can suffer sunburn if overexposed. There is no cure — only prevention. Manage foliage diseases that cause leaf loss, and prune carefully to protect developing fruit.
Early and late blight
These fungal diseases thrive in warm, wet weather and appear as irregular, greenish water-soaked spots on lower leaves and stems. Spots enlarge quickly, forming purplish-black lesions that kill the foliage. To prevent blight:
- Avoid overhead watering
- Provide ample space between plants
- Stake and prune to improve air circulation
- Remove diseased leaves
Slow-ripening fruit
Tomatoes ripen fastest at 70°F to 75°F. Temperatures above 85°F can slow the ripening process. Wait for cooler weather to allow fruit to ripen on the vine. You can also harvest tomatoes showing slight color changes and ripen them indoors at room temperature.
Learn more
For additional information, including photos and control strategies, consult the Pacific Northwest Plant Disease Management Handbook.
For general guidance on growing tomatoes, see the Oregon State Extension publication Grow your own tomatoes and tomatillos.
Previously titled Tomato lovers: Grow the best by recognizing and solving common problems
