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Disease and the Tomato Plant

Tomato Pointers

Early blight produces a wide range of symptoms at all growth stages of both potato and tomato which include damping-off, collar rot, stem cankers, leaf blight, and fruit/tuber rot.

Seedlings grown from infested seeds may damp off soon after emergence because large lesions develop at the ground line on stems of transplants or seedlings. Collar rot occurs when the young stem becomes girdled with dark lesions at the soil level.

The infected leaf has circular lesions of about 1.2 cm (1/2 inch) in diameter. Dark, concentric circles (circles with a common center) are found within these lesions. Infection usually begins on the lower, older leaves and progresses up the plant. Infected leaves eventually wilt, die, and fall off. Early blight lesions show a generally dry "bulls-eye" angular pattern that do not usually spread very far and rarely affect petiole tissue, as the progress of the fungus is stopped by the veins of the leaf.

An infected stem has small, dark, slightly sunken areas that enlarge to form circular or elongated spots with lighter-colored centers. Concentric markings, similar to those on leaves, often develop on stem lesions.

Infestation during the flowering stage of tomato causes the blossoms to drop. The fruit stems are spotted with lesions that lead to loss of the young fruits.

An infested tomato fruit has dark, leathery sunken spots, usually at the point of the stem attachment. These spots may enlarge to involve the entire upper portion of the fruit, often showing concentric markings like those on leaves. Affected areas may be covered with velvety black masses of spores. Fruits can also be infected during the green or ripe stage through growth cracks and other wounds. Infected fruits often drop before reaching maturity.

Prevention and control
1. Proper selection of seeds for sowing/planting. Make sure that these are disease-free and not taken from plants that were previously infested by the early blight disease.

2. Plow under all the crop residues after harvest to physically remove the spore source from the topsoil.

3. Practice crop rotation. Fields should not be planted with tomato, potato, pepper, or eggplant for at least 2 cropping seasons so that these hosts are not present for the spores to thrive on.

4. Remove weeds as these may serve as the alternate hosts.

5. Practice the recommended plant spacing to promote good air circulation. Staking tomato plants provides proper aeration to the plants.

Tomato Pointers

Blossom-end rot is not caused by a parasitic organism but is a physiologic disorder associated with a low concentration of calcium in the fruit. Calcium is required in relatively large concentrations for normal cell growth. When a rapidly growing fruit is deprived of necessary calcium, the tissues break down, leaving the characteristic dry, sunken lesion at the blossom end. Blossom-end rot is induced when demand for calcium exceeds supply. This may result from low calcium levels or high amounts of competitive cations in the soil, drought stress, or excessive soil moisture fluctuations which reduce uptake and movement of calcium into the plant, or rapid, vegetative growth due to excessive nitrogen fertilization.

Management 1, Maintain the soil pH around 6.5. Liming will supply calcium and will increase the ratio of calcium ions to other competitive ions in the soil.

2. Use nitrate nitrogen as the fertilizer nitrogen source. Ammoniacal nitrogen may increase blossom-end rot as excess ammonium ions reduce calcium uptake. Avoid over-fertilization as side dressings during early fruiting, especially with ammoniacal forms of nitrogen.

3. Avoid drought stress and wide fluctuations in soil moisture by using mulches and/or irrigation. Plants generally need about one inch of moisture per week from rain or irrigation for proper growth and development.

4. Foliar applications of calcium, which are often advocated, are of little value because of poor absorption and movement to fruit where it is needed.

Tomato Pointers

Late Blight: Cultural controls alone won't prevent disease during seasons with wet, cool weather. However, the following measures will improve your chances of raising a successful crop.

1. Plant only healthy-appearing tomato transplants. Check to make sure plants are free of dark lesions on leaves or stems. If starting transplants from seed, air-dry freshly harvested seed at least 3 days.

2. Destroy volunteer tomatoes and potatoes routinely by cultivation or herbicides. Do not let volunteers grow, even on compost piles. Infected tomato refuse should be buried or bagged and put in the trash.

3. Avoid wetting foliage when irrigating, especially in late afternoon and evening.

4. Space, stake, and prune tomato plants to provide good air circulation.

Tomato-lly yours,

Penny Mohney


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