Tuesday, July 8, 2014

Temperamental Tomatoes: Tips for Diagnosing Common Problems

Blossom End Rot.
Juicy red heirlooms and other savory tomatoes varieties are heart's desire of vegetable gardeners, but problems can happen with too much or too little nurturing. Here are common issues with Solanum lycopersicum.


Blossom End Rot
Caused by calcium deficiency in the fruit, resulting from: 1. Lack of soil calcium. 2. Water deficiency, which prevents plant from taking up sufficient calcium. 3. Internal plant water deficit during sudden hot periods. 4. Nutrient imbalances, which reduce calcium movement into fruit.
Control of Blossom End Rot:
• Apply lime and fertilizer at planting time according to soil test report.
• Use mulch to maintain even soil moisture.
• Water plants with 1-1/2 to 2" per week (minus rainfall).
• Plant resistant varieties if you've had problems before (e.g. Homestead or Walker).
• Wait: Problem often levels off/corrects itself after several fruit clusters have set fruit.
• Apply foliar calcium. Calcium Chloride, which is sold commercially by several names such as "Tomato Saver" or "Blossom End Rot Prevented." Spray 2-4 Tbsp/gal at blossom stage/tiny fruit stage and once per week for next 3 weeks. Applying lime to the current crop will not help. Lime is too slow acting to help. (Also susceptible to Blossom End Rot: Eggplant, Watermelon, and Peppers).

Tall, spindly plants
Overdoing nitrogen? Insufficient sun? They prefer 8 hours of sun.

Poor Production
If seeds were planted while temperatures were too cool, the main stem will harden and result in poor production. Tomatoes require a soil temperature of 70° F.

Care When Using Chemicals

Tomatoes are very sensitive to some chemicals, especially 2,4-D.

Blossom Drop
Some varieties will set fruit only within a rather narrow range of night temperatures. Many varieties require night temperatures above 55° F for fruit set, and night temperatures above 75° F inhibit fruit set, causing blossom drop.

All Vines and No Fruit
Caused by excessive nitrogen and/or lack of fruit set. When the blossoms drop, the plant continues in the vegetative state. When weather conditions improve, the plant is likely to set fruit. Avoid excess fertilizer. 

Improving Fruit Set
Pollen is shed most abundantly on bright sunny days between 10 am and 4 pm. In the middle of the day, tap and shake the plant gently or hand pollinate with a small paintbrush.

Fruit cracking
Radial cracking usually occurs when the plant undergoes extremely rapid growth, as when rainy periods and high temperatures follow a long dry period.

Hard white blotchy tissue in tomato
A physiological disorder that is not clearly understood. There is no satisfactory control; some species are less affected than others, but no varieties are immune. Ok to use fruit with small to moderate amounts of blotchiness.

Leaf Rolling
This is usually not a disease problem. The greater the ratio of fruit to leaf area, the more leaves will roll. Pruning off leaves and shoots will intensify rolling, as will moisture shortage. Some varieties are more prone to rolling than others.

Yellowing Leaves
Nitrogen deficiency, or one of the diseases mentioned below.


Leaf-spot pathogens
There are several fungal pathogens causing diseases on the leaves of tomatoes (Septoria leaf spot, Early Blight, Late Blight, etc.). In the early stages of these diseases, a few small (1/16") brown-tan necrotic spots will be seen on the leaves. As the disease progresses, the spots will increase in size and number, and the surrounding tissue will often begin to yellow. Finally the affected leaves will begin to drop off. All of these diseases are favored by hot moist weather and poor air circulation.  
Control of leaf-spot pathogens:
• Staking: provides improved air circulation.
• Sanitation: All diseased and fallen leaves should be removed from the garden during the growth season; remove entire plant at end of season and dispose of them away from garden.
• Fungicides: Will not remove existing lesions but will prevent new lesions from forming and spreading the disease. Fungicides should be applied according to label directions (approximately every 10-14 days) after the first lesions are seen, which is usually in May or June.

Wilt-diseased plants should be destroyed.
Wilt Diseases
All are soil-borne diseases and all are fatal. Once infected, there is no effective chemical treatment. The soil should not be used for tomatoes for several years. Plant resistant varieties in a different area next year. Some of the wilts have a rapid onset and death of the plant, while others have a gradual onset and decline. Diseased plants should be removed and destroyed.

To diagnose: Pull up a dead/affected plant and inspect the roots for galls that look like a string of beads. Control: Plant resistant varieties and rotate.

Phytopthora Root Rot
A fungal disease usually caused by poor drainage. A wide variety of plants are susceptible (azaleas, rhododendrons, camellias, boxwood, etc.) Do not replant the same plant in the same spot; improve drainage before planting anything in the affected area.

What to do for Tomato Diseases
Not much this year. Usually a diseased plant cannot be cured; therefore control must be based on prevention and avoiding spread of any disease already present. (The exception is the fungal leaf spot diseases if control spraying is begun early.) 1. Rotation of crops 2. Use disease-resistant varieties 3. Pull out and destroy affected plants and leaves promptly; do not compost them 4. Incorporate organic matter annually to increase diversity of organisms.

Prepared by: Durham County Master Gardener Volunteer Program  

Revised: October 26, 2007

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