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Tomato plants can develop several abiotic disorders that distort plants and blemish fruits. Abiotic disorders are not caused by a living pathogen, but rather are the result of cultural practices or environmental conditions. Generally, good cultural practices that ensure consistent plant growth will reduce the occurrence of abiotic disorders.
Tomato varieties also differ in susceptibility to these disorders. By trial and error you can find the best varieties for your location. In addition, seed catalogs often give varietal information that may help avoid problems.
Leaf roll is a physiological disorder of tomatoes that is most commonly associated with hot dry weather, but can occur in response to other stresses like fast growth, high production, and pruning. Leaf margins roll upward until they touch or overlap in an almost tube like fashion. Affected leaves are firm and leathery to the touch. This disorder is believed to be a strategy to conserve moisture. Lower leaves are commonly affected first. Once leaves roll, they will not unroll even if weather conditions become cool and wet. In severe conditions the entire plant may exhibit leaf roll. Leaf roll does not noticeably reduce plant growth or yield. Some varieties exhibit leaf roll more easily than others. Leaf roll is very common in tomatoes grown in hoop houses.
Blossom-end rot is one of the most common tomato disorders seen in Minnesota. Affected fruit have a tan to black flattened spot at the blossom end of the fruit. Secondary fungi and bacteria can enter the blossom end rot area, resulting in further decay of the fruit. Blossom end rot can appear on fruit in any stage of development, but it is most common when fruit are one-third to one-half grown. The first fruit produced by the plant are often most severely affected. Fruit that develop later in the season on the same plant can be unaffected.
Blossom-end rot is caused by a calcium deficiency in the tomato plant. Although blossom end rot means that the plant does not have enough calcium with in the developing fruit, it does not mean that there is a lack of calcium in the soil. Often blossom end rot occurs as a result of several cultural or environmental factors that affect the plants ability to take up calcium. Fluctuations in soil moisture, heavy applications of nitrogen fertilizer, and injury roots can all predispose tomato plants to blossom end rot.
The amount of calcium salt available to the plant decreases rapidly in the presence of excessive salts such as potassium, magnesium, ammonium, and sodium. Extreme fluctuation in moisture can also reduce the availability of calcium salts needed by the plant. Heavy applications of nitrogen fertilizers and abundant rain cause rapid and luxuriant plant growth and predispose the fruit to blossom-end rot, especially during periods of dry, hot weather.
Blossom-end rot can be minimized by maintaining a uniform supply of moisture through regular watering and soil mulches, applying fertilizer according to the results of a soil test, and avoiding root injury by not cultivating within 1 foot of the base of the plant.
Sunscald occurs on tomato fruit that have been exposed to too much sun. This is common in plants that are suffering leaf loss from a leaf spot disease or insect feeding, but can also occur on plants that are over pruned or on fruit that are otherwise exposed to the sun.
Sunscald results in a pale yellow to white spot on the side of the fruit facing the sun. This area may become a flattened, grayish-white spot. The surface may dry out to a paper like texture. Sunscald spots are frequently invaded by decay-causing fungi and bacteria that further rot the fruit.
The best way to avoid sunscald is to maintain a healthy tomato plant through management of insect and disease pests that defoliate tomatoes.
Growth cracks result from extremely rapid fruit growth. This may be brought on by periods of abundant rain and high temperatures, or can occur when water is suddenly available to the plant through rain or irrigation after a period of drought. Cracks may radiate from the stem end of the fruit or may encircle the fruit. Cracks are often invaded by secondary fungi and bacteria that further rot the fruit.
Maintaining even moisture by watering regularly and mulching the soil around the tomato plant can help reduce growth cracks. Varieties differ in susceptibility to cracking, and variety descriptions may be helpful in choosing a plant less likely to crack.
Catface is a condition involving malformation and scarring of fruits, particularly at the blossom end. Affected fruit are often somewhat flat with a corky brown scar covering the base of the fruit. Catfaced fruit can have cavities extending deep into the flesh.
The causes of catfacing are not definitely known, but it is generally agreed that any disturbance to flowers or flower buds can lead to abnormally shaped fruits. Cold temperatures and contact with hormone-type herbicide sprays are commonly believed to be responsible for catface.
Large fruited tomatoes are more susceptible to catface than small fruited tomatoes. In addition some varieties are particularly prone to catface and should be avoided if catface has been a problem in the past.
Tomatoes are very sensitive to injury from broadleaf herbicide chemicals. These are commonly used for controlling weeds like dandelions, plantain and clover in home lawns. The most common injury symptoms observed are caused by phenoxy herbicides such as 2,4-D (2,4-dichlorophenoxyacetic acid) and dicamba (substituted benzoic acid). These chemicals are growth regulator, hormone-type weed control chemicals. Tomato plants usually come in contact with the chemical through spray drift or the use of a sprayer that was previously used to apply the herbicide. It is also possible to expose tomato plants to broadleaf herbicides by using grass clippings from lawns recently treated for these weeds as mulch in the vegetable garden. Be sure to follow any and all herbicide label directions regarding the use of treated grass clippings for mulches in vegetable gardens. While there is usually little threat of injury once the lawn has been mowed four to six times after the herbicide was applied, if you are still concerned, leave the clippings on the lawn where they can decompose and provide some nutrients and organic matter back to the lawn.
Contaminated plants show one or more of the following symptoms depending on the degree of exposure and age of plant at exposure. Older leaves are excessively pointed, down-curved, or rolled with prominent light-colored veins; young leaves do not fully expand and are narrow and elongated with parallel veins; stems are split, distorted, or brittle; and fruits are catfaced or irregularly shaped.
Plants exposed to small amounts of phenoxy herbicides will outgrow the symptoms without seriously reducing yield or fruit quality. Harvest might be delayed, however. Plants do not recover from severe damage by herbicides.
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