- Tomato plants can develop disorders that distort plants and blemish fruits.
- Some disorders are not caused by diseases, but are the result of cultural practices or environmental conditions.
- Generally, good cultural practices that ensure consistent plant growth will reduce these types of disorders.
Different tomato varieties may be more or less likely to develop these disorders.
You may have to try out different tomatoes before finding varieties that do well in your location. Seed catalogs often give information that can help you choose varieties that avoid problems.
Leaf roll is a physical disorder of tomatoes that is associated with hot dry weather, but can occur in response to other stresses like fast growth, high production and pruning. This disorder is believed to be a strategy to conserve moisture.
- Leaf margins roll upward until they touch or overlap in an almost tube like fashion.
- Affected leaves are firm and leathery to the touch.
- 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.
Cause of the disorder
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 within 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, such as
- fluctuations in soil moisture
- heavy applications of nitrogen fertilizer
- injury to roots
The amount of calcium salt available to the plant decreases rapidly when there is too much of other 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 can cause blossom-end rot, especially during periods of dry, hot weather.
How to control blossom-end rot
Blossom-end rot can be minimized:
- Keep the soil moist through regular watering
- Apply mulch to retain moisture between watering
- Apply fertilizer according to the results of a soil test
- Avoid injuring roots; don't cultivate 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 by managing insects and diseases that destroy or eat tomato leaves.
Extremely fast fruit growth can cause growth cracks. This may be caused by periods of abundant rain and high temperatures, or can happen when it rains or you water water plants 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 may be caused by
- Any disturbance to flowers or flower buds
- Cold temperatures and
- Contact with hormone-type herbicide sprays
Large tomatoes are more susceptible to catface than small tomatoes. Some varieties are particularly prone to catface and should be avoided if it 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 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 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.
Symptoms of herbicide injury
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
- 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.
Reviewed in 2018