Tomato Plant Diseases

Learning how to grow tomatoes is a popular vegetable gardening pastime. And nothing ruins a homemade crop of tomatoes faster than tomato plant diseases such as tomato wilt and tomato pests. Use this guide to identify and treat tomato pests and tomato plant problems as soon as they start in your homegrown tomato garden patch.

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From containers to expansive garden plots, growing tomatoes is a popular and relatively easy way to harvest at least some of your own produce. In fact, tasty and easy-to-grow tomatoes are the most popular garden vegetable. However, tomato pests and tomato plant diseases such as tomato wilt can harm your tomato crop.

Don't let those potential problems scare you away. Growing healthy, pest- and disease-free tomato plants is relatively simple. Keep your plants healthy by rotating crops, planting disease-resistant varieties, spacing plants properly, mulching, and watering at least 1 inch per week.
Start your tomatoes off right. 

As tomato plants grow, keep an eye out for tomato pests and tomato plant diseases such as tomato wilt that may come in the form of fungi, bacteria, or viruses.
Get tips for growing healthy tomatoes.

In the fall, if you have had tomato plant disease problems or tomato pests  of any kind, remove the entire plant.

Rotate tomatoes so they grow in the same ground only every four years or so. Many tomato plant diseases and tomato pests lurk in the soil.

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Tomato Plant Disease: Septoria Leaf Spot

Septoria leaf spot is one of the most common tomato plant leaf diseases. You can first detect this fungus as it creates a small, circular spot with a grayish-white center and dark edges. Small black spots may show up in the center. Affected tomato plant leaves turn yellow, wither, and fall off.

Long periods of warm, wet weather contribute to this tomato plant disease, and splashing water spreads spores to other leaves.

Control leaf spot by not crowding your tomatoes. Leave enough space so air circulates and dries leaves.

Avoid overhead watering. When watering tomatoes, water at the base of the plant. Also, water in the morning so wet leaves have time to dry before evening.

A fungicide formulated for tomatoes can be used to treat affected plants.

Tomato Plant Disease: Anthracnose

Follow the same procedures used for septoria leaf spot against the tomato plant disease anthracnose. This fungus shows up as a small, circular, indented area on tomato fruits. Eventually, rings surround the original spot.

The flesh of the fruits may rot completely through, especially on overripe tomatoes, so keep fruits picked as they ripen.

Spores are spread by rain splash, and the fungus is most common in warm, wet weather.

Tomato Plant Disease: Fusarium and Verticillium Wilt

These tomato plant wilt diseases are caused by fungi in the soil that enter through young roots, then begin to plug the vessels that move water to the roots and stems of the plants. Without water, the plants begin to suffer from tomato wilt on sunny days, although they appear to recover at night. Tomato wilting may first appear in the top or lower leaves of the plant, causing them to lose color, then die back from the tips. The process of tomato wilt continues until the entire plant is affected.

Heirloom tomato varieties that have not been bred to withstand these diseases are commonly attacked by tomato wilt. New strains of this tomato plant disease attacks cultivars that are resistant to only one type of tomato wilt.
Learn about growing heirloom tomatoes.

Fusarium wilt is most common as a tomato plant disease in warm-weather regions and occurs during the warmest weather in cool areas.

To avoid these tomato plant diseases, plant tomatoes bred for disease resistance. They should be labeled V (for verticillium), F, FF, or FFF (for fusarium variations). See "Understand the Tomato Code," below, for more about tomato plant labels.

Avoid overwatering tomato plants; just because a plant is wilted doesn't mean it needs more water. Check the soil; if the soil is dry, then water the plant.

If your tomatoes are affected by one of these tomato wilts, remove and destroy all affected plants. Do not place them in your compost pile. Avoid using this location for tomato, eggplant, potato, and pepper plants for four to six years, because the fungi that causes the tomato wilt remain in the soil. Corn and beans won't be affected.

Keep weeds out of affected areas because their roots can continue feeding these pathogens.

Tomato Plant Disease: Early Blight (Alternaria)

Another tomato plant disease fungus, Alternaria, also causes leaf spot or early blight. Lower leaves show brown or black spots with dark edges, almost like a target. Stem ends of fruits may be attacked, showing large, sunken black areas with concentric rings.

This tomato plant disease fungus usually strikes after plants set fruit.

Tomato Plant Disease: Late Blight

The tomato plant disease late blight, caused by the fungus Phytophthora infestans, occurs during periods of cool, rainy weather that may come at the end of a growing season. It looks almost like frost damage on leaves, causing irregular green-black splotches. Fruits may have large, irregular-shape brown blotches that quickly become rotten.

This tomato plant disease fungus also affects potatoes and can be transferred from them.

Use the same controls as for septoria leaf spot.

Tomato Plant Disease: Mosaic Virus

Mosaic virus attacks many kinds of plants and is common in tomatoes. The tomato plant disease mosaic virus doesn't kill the plant, but it diminishes the number and quality of fruits.

The virus gets its name from the markings that resemble a mosaic of light green and yellow on the leaves and mottling on the fruits of affected plants. Leaves may also grow in misshapen forms, resembling ferns.

Because the virus must enter through a cut in the plant, avoid handling the plant. Anyone who uses tobacco can easily transmit the disease; wash hands thoroughly with soap to cut the risk of infection.

Avoid this virus by planting resistant cultivars and not replanting in areas that previously hosted the problem.

Tomato Plant Bacterial Diseases

Tomatoes can fall prey to a number of tomato plant bacterial diseases, including bacterial spot, bacterial speck, and bacterial canker. They're all slightly different but appear as spots on leaves and fruits.

Use the same controls as for septoria leaf spot. Grow disease-resistant plants. Avoid rotating the same ground with peppers, which can host the same diseases.

Avoid pruning and tying plants, because the bacteria can enter any openings made during these procedures.

Fixed copper sprays may reduce the spread if applied as soon as symptoms begin.

Understand the Tomato Plant Disease Code

Disease resistance has been bred into many tomato varieties. The letters behind the names are codes showing what diseases and insects the tomato plants are bred to resist, including:

V             Verticillium wilt
F              Fusarium wilt
F              Fusarium wilt races 1 and 2
FFF           Fusarium wilt races 1, 2, and 3
N              Nematodes
A              Alternaria alternata (stem canker or early blight)
T              Tobacco mosaic virus
St            Stemphylium (gray leaf spot)
TSWV       Tomato spotted wilt virus

For example, the label on Big Beef VFFNTA Hybrid, a winner of a 1994 All-America Selections award, tells you it is bred to resist verticillium wilt, fusarium wilt races 1 and 2, nematodes, tobacco mosaic virus, and Alternaria, an early blight.

Learn about tomato blossom end rot, another tomato problem. 

Choose the right tomato for your garden.

Learn more about heirloom varieties.

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