With a little time and attention, you can grow beautiful tomatoes in your home garden. Keep an eye out for these pests and diseases throughout the season to keep your plants and fruits healthy.
Preventing disease before it starts
1. Plant resistant varieties with good horticultural characteristics. Read the symbols on the plant packaging to determine disease resistance.
2. Purchase disease-free transplants from a reliable source.
3. Maintain a disease control program throughout the growing season.
4. Establish good cultural and sanitation practices, such as:
- Proper soil preparation
- Early detection and removal of diseased leaves and plants
5. Rotate tomatoes and solanaceous crops each year to reduce persistence of disease and reinfection.
Tomato diseases : Foliage
Early blight can affect the foliage, stems and fruit of tomatoes.
Symptoms: Ironically, symptoms of early blight usually appear near the end of the growing season. Dark spots with concentric rings develop on older leaves first. The surrounding leaf area may turn yellow. The leaves of severely affected plants may die prematurely, exposing the fruits to sun scald. Plants are most susceptible when they are under stress from another disease or nutrient deficiency.
Management: Early blight fungus overwinters in plant residue and is soil-borne. It can also be present on transplants. Remove affected plants and thoroughly clean fall garden debris. Wet weather and stressed plants increase the likelihood of attack. Minimize leaf wetness by watering plants in the morning or at the base of the plant.
If early blight appears, apply one of the following fungicides at 7-10 day intervals.
Copper and/or sulfur sprays can prevent further development of the fungus. Bonide Fung-onil® is also an effective treatment and contains Chlorothalonil as the active ingredient.
Gray leaf spot
Gray leaf spot affects only the leaves of tomatoes, starting with the oldest leaves.
Symptoms: Small, dark spots that can be seen on both the top and bottom surfaces of the leaves. The spots enlarge and turn a grayish brown. Eventually, the centers of the spots crack and fall out. Surrounding leaf areas turn yellow and the leaves dry and drop. Fruit production is inhibited.
Management: Warm, moist conditions worsen gray leaf spot problems. Remove all affected plants and fall garden debris. Select resistant varieties.
Late blight affects both the leaves and fruit of tomatoes. Late blight is the disease responsible for the Irish potato famine.
Late blight spreads rapidly in cool, wet weather. It can appear at any time during the growing season, but usually appears in late summer or early fall. Late blight fungus overwinters in plant residue and is soil-borne.
Symptoms: Greasy-looking, irregularly shaped gray spots appear on leaves. A ring of white mold can develop around the spots, especially in wet weather. The spots eventually turn dry and papery. Blackened areas may appear on the stems. The fruits also develop large, irregularly shaped, greasy gray spots.
Management: Copper sprays and chlorothalonil offer some control at the first sign of disease. Controlling late blight is difficult once the disease is established. Remove and destroy diseased plant parts as they appear.
Septoria leaf spot
Septoria leaf spot is sometimes mistaken for late blight.
Symptoms: With septoria leaf spot, the papery patches on the leaves develop tiny, dark specks inside them. Older leaves are affected first.
Management: Copper sprays are somewhat effective in halting the spread of symptoms. Cultural control is the best way to prevent septoria leaf spot. Water plants at the base rather than overhead, stake plants to increase air circulation and apply mulch around the base of the plant to minimize water splash.
Septoria overwinters in plant debris and soil. Be sure to remove infected plants at the end of the growing season.
Verticillium wilt is caused by a soil-borne fungus. It can affect many vegetables. The fungus can persist in the soil for many years, so crop rotation and selection of resistant varieties is crucial.
Symptoms: Wilting during the hottest part of the day and recovering at night, yellowing and eventually browning between the leaf veins starting with the older, lower leaves and discoloration inside the stems. In addition, infected plants often have a characteristic V-shaped lesion at the edge of the leaf occurring in a fan pattern.
Verticillium wilt inhibits the plant’s ability to take in water and nutrients and will eventually kill the plant. Verticillium wilt is more pronounced in cool weather.
Management: Whenever possible, plant resistant varieties. Remove and destroy any infested plant material to prevent the fungi from overwintering and creating new infections. Keep plants healthy by watering and fertilizing as needed. Gardens should be kept weed-free since many weeds are hosts for the pathogen.
Fusarium wilt is is a fungus that can attack tomatoes at any time during the growing season. Fusarium wiltis usually enters the plant through young roots, then grows into and up the water-conducting vessels of the roots and stem. Currently, there are two strains that infect tomatoes.
Symptoms: Fusarium wiltis symptoms begin in tomatoes as slight vein clearing on outer leaflets and drooping of leaf petioles. Later the lower leaves wilt, turn yellow and die and the entire plant may be killed, often before the plant reaches maturity. In many cases a single shoot wilts before the rest of the plant shows symptoms, or one side of the plant is affected first. If the main stem is cut, dark-brown streaks may be seen running lengthwise through the stem.
Management: Management mostly consists of cultural practices much like those used to prevent verticillium. Whenever possible, plant resistant varieties. Remove and destroy any infested plant material to prevent the fungi from overwintering and creating new infections. Keep plants healthy by watering and fertilizing as needed. Gardens should be kept weed-free since many weeds are hosts for the pathogen.
Tobacco mosaic virus
Tobacco mosaic virus is one of the most common causes of virus diseases of plants in Minnesota.
Symptoms: Virus produces mosaic-like symptoms on plants. These are characterized by intermingled patches of normal and light green or yellowish colors on the leaves of infected plants. Tobacco mosaic virus damages the leaves, flowers, and fruit and causes stunting of the plant. The virus almost never kills plants but lowers the quality and quantity of the crop, particularly when the plants are infected while young.
Management: There are no known chemical cures for plant viruses. Control of tobacco mosaic virus is primarily focused on reducing and eliminating sources of the virus and limiting the spread by insects. Therefore, sanitation is the single most important practice in controlling it.
Tonkadale recommends the following products for treating tomato and vegetable fungal diseases: Copper Fungicide, Fung-onil and Sulfur Funcide from Bonide.
Tomato diseases: Fruit
Anthracnose is a very common fungus that causes tomato fruit to rot.
Symptoms: Small, round, sunken spots appear on the fruit. The spots will increase in size and darken in the center. Several spots may merge as they enlarge. The fungus is often splashed onto the fruit from the soil. It can also take hold on early blight spots or dying leaves.
Wet weather encourages the development of anthracnose. Overripe tomatoes that come in contact with wet soil are especially susceptible.
Management: Anthracnose overwinters on infected plant debris, so it is very important to dispose of rotten fruit and infected plants. Pick fruit promptly to avoid over-ripening.
Copper sprays offer some resistance. Remove the lower 12″ of leaves to avoid contact with the soil. Remember not to water the leaves, just the base of the plant.
Blossom end rot is thought to be caused by insufficient calcium. This calcium deficiency is most likely caused by irregular watering and a fluctuation in water levels. Without enough water, the calcium, which is being used first for foliage growth, doesn’t make its way to the fruits. Other factors may include:
- Too much nitrogen fertilizer.
- Too much salt in the soil.
- Root damage and a soil pH that is too high or too far below the optimum 6.5.
Symptoms: Rotting fruits. These can’t be saved.
Management: Remove the affected fruits, and make sure the plants are getting at least an inch of water per week.
To prevent blossom end rot, enrich your soil at the time of transplant with a specialty, calcium-based tomato fertilizer such as Tomato Tone®.
When signs of blossom end rot appear, products that can be sprayed directly on the fruit to stop it. We recommend Rot-Stop®.
Gray wall is essentially a ripening problem.
Symptoms: Green fruits may have a gray cast or gray blotches. Ripe fruit will have green or brown areas on the inside of the fruit.
Management: Good growing conditions will prevent gray wall. Make sure plants aren’t heavily shaded, and are receiving even watering and sufficient fertilizer. Ensure that the soil is not compacted around the roots. Cool temperatures and stressed or unhealthy plants also contribute to this problem.
Sunscald occurs on tomato fruit that has 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.
Symptoms: 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.
Management: 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.
Symptoms: Growth cracks may radiate from the stem end of the fruit or may encircle the fruit. Growth cracks are often invaded by secondary fungi and bacteria that further rot the fruit.
Management: Maintain even moisture by watering regularly and mulching the soil around the tomato plant to 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. 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.
Symptoms: Affected tomatoes 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.
Management: Large tomatoes are more susceptible to catface than small tomatoes. Some varieties are particularly prone to catface and should be avoided if catface has been a problem in the past.
Some species of cutworms migrate from the south, while others are native to Minnesota and overwinter in the soil each year as eggs or larvae.
Symptoms: Cutworms are most devastating in the vegetable garden in the early spring as they chew through the stems of young, tender plants.
Management: Remove weeds and plant residue to help reduce egg-laying. Till your garden before planting, which helps expose and kill overwintering larvae.
You can control cutworms by placing aluminum foil, cardboard collars or tin cans around transplants. This creates a barrier that physically prevents cutworm larvae from feeding on plants. When placing these collars around plants, make sure one end is pushed a few inches into the soil, and the other end extends several inches above ground.
The use of insecticides in home gardens is usually not necessary, but you can protect plants if you are experiencing a severe problem. Tonkadale recommends products containing permethrin such as Bonide Eight®.
Tomato hornworms are very large caterpillars that have a horn-like tail. Large numbers of caterpillars can quickly defoliate plants. Tomato hornworms feed only on solanaceous plants such as tomatoes, potatoes, eggplant and peppers.
Symptoms: Tomato hornworms caterpillars feed initially on the leaves on the upper portions of the plants. The green caterpillars blend in with the plant canopy, and can go unnoticed until most of the damage is done. As they feed, they create dark green or black droppings that can be conspicuous.
Management: The best management strategy is to physically inspect tomato plants for hornworms and remove them at the first sign of damage. Insecticides are generally not needed, but products such as insecticidal soap and Captain Jack’s Dead Bug Brew are effective. Remove plant debris from the garden and till the soil under each year to keep hornworms from overwintering in residual plant material.
Root knot nematodes
Root knot nematodes are obligate parasites that require a host plant to thrive. They live in the soil and reproduce rapidly. RKN attacks are rare in Minnesota because the soil temperatures are not high enough most of the year to support their life cycle.
Symptoms: Plant symptoms appear above ground because of root dysfunction. These include reduced vigor, wilting and nutrient deficiency.
Management: Apply good cultural controls as discussed above and choose resistant varieties.
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Top photo: Septoria leaf spot. All photos courtesy of University of Minnesota Extension.