It’s July and you’ve been anticipating for months your harvest of plump red (yellow, orange, pink, zebra, purple) tomatoes from the tomato plants you’ve been tending since April’s last frost date. Now you watch with dismay as your once lush tomato leaves shrivel and fruit drop off or rot on the vines. What happened? Is it the weather? Are bugs causing the problem or is it something you can’t see operating against your plans for a bountiful crop?
Tomato problems can be caused by many factors including those against your control like weather, diseases borne by air or soil, or factors you can prevent like improper site selection or lack of proper nutrition, watering and garden cleanup and maintenance from year to year. The good news is that most tomato diseases are rarely fatal, especially if problems are caught early and managed properly. Early management is not just important to your tomatoes — tomato diseases can effect other members of the nightshade family — eggplants, peppers and potatoes.
Most of the common tomato diseases are caused by a fungus and therefore conditions that encourage fungal growth – wet, cool, cloudy weather conditions and high humidity — will lead to greater damage. Sometimes insects like thrips and flea beetles will transmit the infection; sometimes the fungus is transmitted from infected soil, and occasionally planting tomato plants too close together will increase the likelihood of infection. General management like selecting blight resistant varieties, rotating crops, using mulch and drip irrigation, and properly spacing plants will help you avoid dealing with tomato diseases. Proper soil preparation and nutrition will also help you start with healthier plants that may be more resistant to disease. You can read more about tomato gardening including best practices in a publication developed by the UT Extension here. And, if you have question about your tomato problems, you can contact your local Extension agent for more information.
The information provided below outlines some of the most common tomato problems in this area but does not include all the possible diseases that can affect tomatoes. In Part 2, we look at other tomato fruit problems and blemishes causes by other, non-pathogenic problems.
|Early Blight||Early Blight is caused by fungus (Alternaria solani) that overwinters in soil and plant debris. It can also originate from seeds and tomato sets and depends less on weather conditions than Late Blight. Early Blight can affect the foliage, stems and fruit. The symptoms are dark spots that radiate outward, turning the surrounding tissue yellow. Usually, the older leaves are affected first, and may die and drop off the plant leaving the young tomatoes exposed to sunlight and scalding. Wet weather and stress increases the plants susceptibility to this fungal infection.||Since Early Blight overwinters in the soil, clean your garden thoroughly of plant debris in the fall. Mulching plants helps to create a barrier between the soil and plants so that rain won’t contribute to splashing the fungus upward onto the plant leaves. Using drip irrigation helps to prevent contamination as well. Copper and/or sulfur sprays can prevent further development of the fungus.|
|Botrytis Blight or Gray Mold||Gray Mold (Botrytis cinerea) is also caused by a fungus that thrives in wet weather. The symptoms are similar to Early Blight, but can inflict a plant at or just the soil level and kill the plant by girdling the stem. The fungus can also develop on the flower and infect move from the flower to the main stem, the stem turning beige to white. Other vegetables can be affected, including snap and lima beans, cabbage, lettuce, muskmelon, pea, pepper and tomato.||Wet/humid conditions accelerate the infection and the fungus can be transmitted by garden debris, infected soil and transmission from plant to plant. Remove plant debris in the fall, remove infected plants and select resistant varieties. Fungicides are only protective and will not suppress an established infection.|
|Late Blight||Most notorious for causing the Irish Potato Famine of the mid-1800s, Late Blight comes in later in the season, spreads rapidly and affects the leaves and fruit. Caused by a fungus-like pathogen (Phytophthora infestans) affected leaves have greasy looking, irregularly shaped gray spots. 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 fruit also develop large, irregularly shaped, greasy gray spots.||Copper sprays and fungicides offer some control but not a cure. Since it spreads to potatoes, it also overwinters in potato debris and seed, even in colder areas. Remove all debris and don’t save seed potatoes.|
|Septoria Leaf Spot||Septoria Leaf Spot (Septoria lycopersici) is sometimes mistaken for Late Blight. The centers of the spot are gray or tan, and as the spots mature, dark brown pimple-like structures will develop. Older leaves are affected first. The fungus may overwinter on other plants related to tomatoes including horsenettle, and black nightshade. Tomato seeds may carry the spores as well.||Copper sprays and fungicides are somewhat effective at halting the spread of symptoms. Make sure you obtain seeds from a reliable, disease-free source.|
|Southern Blight||As with the other blights described here Southern Blight is caused by a fungus, Sclerotium rolfsii. Dark, round spots will appear on the lower stem and both the outer and inner stem will become discolored. A white mold eventually covers the lesion and surrounding moist soil. Southern Blight fungus girdles the tomato stem and prevents the plant from taking up water and nutrients. Young plants may collapse at the soil line. Other vegetables that can be affected are cucurbits (melon, squash, pumpkins), crucifers (cabbage, cauliflower, broccoli) and legumes (beans, peas).||Crop rotation seems to help. There has also been some evidence that extra calcium and the use of fertilizers containing ammonium offer some protection.|
|Verticillium Wilt||This soil-born fungus (Verticilliurn ablo-atrum) can affect over 200 plant species. The fungus can persist in the soil for many years, so crop rotation and selection of resistant varieties is crucial. Symptoms include: 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. The name “Wilt” can be misleading, as sometimes the leaves will turn yellow, dry up and never appear to wilt. The spots that appear on the leaves can also be mistaken for early blight, but lack the bulls-eye ring. Verticillium Wilt inhibits the plants ability to take in water and nutrients and will eventually kill the plant. Verticillium wilt is more pronounced in cool weather.||Remove affected plants and choose resistant varieties. Rotate your tomato crops in long cycles (4 to 5 years is optimal).|
|Anthracnose||Anthracnose is a common fungus (Colletotrichum coccodes) that can cause rotted fruit. The fungus overwinters in garden soil on garden debris. The spores can be transmitted by insects like flea beetles and leaves infected by blight are also susceptible to infection. 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.||Anthracnose is more prevalent in poorly drained soils, so plant tomatoes on well-drained land. Copper sprays offer some resistance. Remove the lower 12″ of leaves, to avoid contact with the soil. Don’t water the leaves, just the base of the plant. Also, avoid through 3- to 4-year crop rotations.|
|Blossom End Rot||Blossom End Rot is a leather-like decay of the blossom end of the fruit that enlarges as the fruit rots. It is generally attributed to a lack of calcium during fruit set which can be caused by too high nitrogen fertilizer and uneven watering which results in fluctuations of nutrients available to the plant during fruit production.||Be sure to lime your garden according to soil test recommendations because it is calcium carbonate and supplies calcium to the soil. Also, mulch and use drip irrigation to provide uniform soil moisture.|
|Buckeye Rot||Buckeye Rot is caused by a fungus (Phytophthora parasitica) that can cause fruit rot of tomatoes, peppers and eggplant. The symptoms are similar to Blossom End Rot, except that the rot appears as alternating light and dark rings on green fruit. On ripened fruit the rotting area will appear water soaked, but not dark in color. The affected area is smooth, distinguishing it from Late Blight, which has a rough surface. This same fungus can cause damping-off of seedlings, stem cankers near the soil line and leaf blight, although not as common.||Grow tomatoes in well drained soil or raised beds, and stake them to prevent the fruit from making contact with the soil.|
|Gray Wall (Blotchy Ripening)||Gray Wall is essentially a ripening problem. Symptoms: The green fruits may have a gray cast or gray blotches. Ripe fruit will have green or brown areas on the inside of the fruit. It is not known what causes graywall but there is some association between the condition an low potassium, low boron, or high nitrogen levels in the soil. The disorder is also more common when the weather is very hot and cloudy.||Good growing conditions will prevent gray wall.|