Guide to Growing Tomatoes - Common Tomato Disorders
Tomato Growing Tips (Part 2 of 2)
Here are some of the more common tomato disorders that result from nonliving (abiotic) causes often attributable to environmental or cultural factors, or simply to the plant’s genetic makeup.
Problems
Blossoms fall off, plant fails to set fruit.
Probable causes: Night temperatures too low (below 55° F), daytime temperatures too high (above 90° F), excessive smog, excess nitrogen fertilizer, too much shade, plants set out too early in spring, and/or poorly adapted variety.
Control: Hormone sprays (from garden centers) can improve fruit set during low temps, but not high temps. Tapping on blossom stems 3 times a week when blossoms are open at midday may improve pollination and help set fruit.
Yellow or yellow-orange colored fruit instead of normal red.
Probable causes: Overexposure to sunlight.
Control: Maintain plant vigor to produce adequate leaf cover. Avoid over-pruning. Provide partial shade (i.e., shade cloth) during the hottest part of day.
Older leaves suddenly roll upward and inward, become stiff, brittle and leathery.
Probable causes: High light intensity and high soil moisture, particularly when plants are heavily pruned. Some varieties are more susceptible.
Control: Maintain even soil moisture, provide shade during hottest part of the day, or try a different variety.
Blossom End Rot—water–soaked spot on blossom end of fruit enlarges and darkens, becomes sunken and leathery.
Probable causes: Calcium and water are out of balance in the plant, aggravated by high soil salt & fluctuating soil moisture.
CONTROL: Maintain even soil moisture, add organic matter to improve water retention and avoid heavy applications of nitrogen fertilizer. Soils deficient in calcium may be amended with gypsum.
Puffiness—tomato resembles a bell pepper with normal outer walls and a hollow area inside.
Probable causes: Temperatures that interfere with pollination such as above 90 degrees, or below 55 degrees, low light, excessive nitrogen fertilizer, heavy rainfall (causing bees to stay home).
Control: Avoid heavy nitrogen fertilizer, select varieties suitable to your microclimate.
Catfacing—circular concentric cracks around the stem end, cracks radiating outward from the stem, malformation and cracking at the blossom end.
Probable causes: Periods of fast growth with high temp and high soil moisture, wide fluctuations in soil moisture, wide difference in day and night temperatures. Some varieties are more susceptible.
Control: Keep soil evenly moist, maintain good leaf cover or provide shade during hottest part of day, apply organic mulch 3-4 inches deep to moderate soil temperature.
Besides these common abiotic disorders, gardeners often discover damage to foliage and fruit caused by a variety of pests including hornworms, fruit worms, pinworms, stink bugs, whiteflies, and leaf miners.
Resources:
- For photographs and information to help you identify and manage pests, refer to the UC Integrated Pest Management for Tomatoes at: http://ipm.ucanr.edu/PMG/GARDEN/VEGES/tomato.html
- For specific pests, see the UC IPM Pest Notes at: http://ipm.ucanr.edu/PMG/menu.homegarden.html. Or, contact the UC Master Gardener Program in Contra Costa for assistance. To reach the Help Desk, call (925) 608-6683 or email ccmg@ucanr.edu.