By Janice Aulisio
VCE Southside Master Gardener
I am sure we are waiting to bite into our first big homegrown tomato! Nothing is quite like the taste and anyone can master growing great tomatoes by following a few simple rules. Start with healthy soil, plenty of sunlight, support the stems with stakes or cages, plant seedlings deep, remove lower leaves, water deeply from the roots, know your soil type (a soil test is recommended) and be sure to plant the right type for your area. Many issues can be avoided by purchasing varieties that are resistant to some of the diseases listed below. Following these steps will be very helpful in getting a good crop of tomatoes, but there are different problems that can strike your plants and I am sure you may have encountered some of them. Let’s take a look and see what they are and how we can avoid and treat your plants effectively.
Picking a ripe tomato from your garden is one of the season’s thrills. Look for disease resistant varieties and maintain good spacing and irrigate the soil and not the plant to minimize disease problems.
Early blight (Alternaria solani) affects the leaves early in the growing season. It appears as little brown spots on the leaves and spreads quickly. The leaves will fall off. This is a fungus that survives in the soil over winter. Easiest way to prevent it is to mulch right after planting which prevents spores in soil from creeping up the plant. Snip off infected leaves to prevent spread. Next year be sure to plant the tomatoes in a different area of your garden. (I plant in straw bales and do not have this problem).
Septoria leaf spot (Septoria tritici) covers your tomato leaves with small circular spots. The centers are gray-white with dark edges, turning the leaves yellow before falling off. It occurs most often with warm and wet weather. Prevent this by keeping your garden neat and not planting too close together so air can circulate around leaves. Cut off infected leaves when they appear. If the problem persists, a fungicide may be needed to kill spores or you may have to dig out beds and replace soil.
Fusarium wilt (Fusarium oxysporum) is usually found further south, but can appear anywhere. It is capable of wiping out whole fields of tomato plants. Drooping stems and wilting results in the death of the plant. Rotate tomatoes and buy wilt-resistant varieties. Once soil is infected it is extremely difficult to eradicate!
Verticillium wilt doesn’t always cause wilting, but the leaves will become yellow and dry. It can spread quickly to other garden plants. It affects the plant xylem vascular tissues which makes it difficult for the plant to get water and nutrients from the soil. This disease occurs most often in cooler weather. If your plants get infected, move healthy ones to another area and don’t plant new ones there for at least 4 years! (Peppers, eggplants and potatoes should not be planted there either). Again, buy wilt-resistant varieties.
Anthracnose (Colletotrichum phomoides) is a fungus that is one of the most common tomato plant diseases. It is characterized by small sunken areas on the leaves and will eventually rot the plant and fruit. It thrives in hot, wet weather and can also afflict potatoes and onions. Remove leaves from lower 12 inches of the plant to keep foliage from contact with wet soil. Don’t overwater your plants and avoid growing tomatoes, peppers and eggplants (members of the nightshade family) in the same spot next season. You could try carrots, beets and other root vegetables.
Most all gardeners have had experience with blossom end rot which is caused by deficient calcium in the soil or the soil is alkaline and watered unevenly. If you see dark enlarged spots on the bottom of the fruit, this is the problem. Enrich your soil with calcium and water regularly and evenly. Remove fruits with rot and test your soil. Tomatoes like a pH
of 6.0 to 6.5. If too alkaline, you could add sphagnum peat to make it more acidic.
Powdery mildew occurs in late summer or fall or if growing in a greenhouse where there is high humidity. Leaves appear discolored, yellowish spots and with a fuzzy powder-like substance on top. Then, they turn brown. It spreads quickly and Neem oil is effective to stop the spread (which has sulfur). Space plants well apart and water at ground level and not on leaves.
Bacterial canker (Clavibacter michiganensis) turns the edges of leaves brown and the centers yellow. This is one of the most difficult to treat. It spreads quickly to other plants which will wilt and die. This is usually seed borne, so make sure to buy either heirloom or organic seeds from a reputable nursery. If it appears, move plants to a different area of the garden and treat with copper hydroxide spray. Keep tomato plants out of the area for at least 3 years. F you do decide to spray a pesticide, make sure you read the label and clearly follow all instructions. Check for the time of application to the time it is safe to harvest.
Fruit cracking is an illness and not a disease. It is caused by a lack of light, water, temperature or nutrients in the plant. It can be prevented by planting in raised bed gardens so you can control moisture levels in the soil. Compost and mulch maintains a more constant moisture level and be sure the soil has sufficient calcium. Remove cracked fruits to avoid ants and other insects resulting in pest problems due to exposed flesh.
Late blight affects the oldest part of the plant and not named for the time of year it appears in your garden. The mature leaves get greenish-black patches, spreads quickly and will progress through the whole garden. Remove all infected plants and move healthy ones elsewhere. Don’t plant nightshade plants in this soil for at least 4 years!
If you follow the simple rules at the beginning you will probably not encounter most of the above issues with your tomato plants. Remember to discard any infected plants properly and do not put them in your compost pile if you have one! Always buy disease resistant varieties whenever possible. Once you know how to manage your tomatoes you will be rewarded with very healthy plants and delicious fruits!
For more information visit the Pest Management Guide: Home Grounds and Animals at Virginia Cooperative Extension or Clemson Extension Home and Garden Information Center.
While we are all still practicing ‘social distancing’ due to COVID-19, and all Halifax County buildings are closed to the public, if you have gardening questions, you can best reach an Extension Master Gardener or Extension staff member by sending an email to firstname.lastname@example.org or email@example.com. If you can’t email, you can call and leave a message at the Extension Master Gardener Help Desk at 434-830-3383, giving us your name, telephone number, and nature of the call. The Help Desk phone is checked timely and someone will get back to you, although it may be from a different telephone number. Keep washing your hands, wear your mask and watch your tomatoes for signs of disease.