Contributed by Tom Elmore
In Western North Carolina, tomato growers may encounter one or more common tomato diseases for our area. Learn how to identify, prevent, and treat issues like blossom end rot, early blight, and late blight in your garden.
Blossom End Rot
The most common tomato complaint that I hear is blossom end rot, which is not really a disease and not really a fungal problem as the expression “rot” implies. Typically this problem is caused by a calcium deficiency which is most often caused by irregular watering. If your garden received lime to adjust the soil acidity, it probably has adequate calcium so the focus should be on a steady supply of moisture to the roots. Mulch helps. During dry periods, water deeply aiming for about one inch of water per week.
Early blight (Alternaria tomatophila) is common in WNC. This fungus is soil borne so mulch helps once the soil has warmed in the spring. Vigorous plant growth can make the infection of the lower leaves insignificant. Several days of cloudy, rainy weather can make it more of a problem since the plant grows more slowly and the fungus grows more quickly. Early blight usually has characteristic target-like dark spots and yellowing of the leaves. Removing infected lower leaves may help prevent spores from being splashed onto upper leaves by rain or overhead irrigation. A happy plant with adequate nutrition often outgrows early blight so it can be ignored.
Late Blight (Phytophthora infestans) is the “Jaws” of tomato diseases in WNC. A week of cool rainy weather can kill your tomatoes and infect all the fruit, just as harvest is about to begin. It is air-borne so symptoms typically start high on the plant with characteristic black “wetted” or water-soaked leaves. It moves very quickly in favorable conditions. Some organic sprays work on late blight based on copper (copper sulfate or copper hydroxide) but copper washes off in rain or overhead irrigation. Copper is a protectant so it must be on the leaves before late blight arrives. Practically speaking, copper works only under plastic to keep the rain from washing it off the leaves. Some growers train their plants under the eaves of their house to avoid rainfall on the foliage.
The best news on late blight is the tomato breeding research at NCSU. Several varieties have been released. We have had good luck with Mountain Magic in late blight years. They are also working on an “heirloom” variety with resistance to both early and late blight – the super tomato for WNC. Look for it in catalogs in the next few years.
Tom Elmore is an organic grower in Leicester NC. Look for the Thatchmore Farm stand at the West and North Asheville Tailgate Markets. Since tomatoes are his favorite food, he grows tomatoes year-round.