Tomatoes may be vegetable garden royalty, but a legion of diseases muster each summer to threaten their reign.
While it’s tough to battle many of them once they’ve invaded, NC Cooperative Extension agents say simple, commonsense management practices can often head off problems.
Among the most common diseases attacking tomatoes is blossom end rot. It’s easy to spot: the bottom of the tomato – the end on the other side of the stem – is black with rot.
A number of wilts also make life interesting for tomato gardeners. Two of them – Verticillium and Fusarium – are reasonably easy to control. Just make sure you pick varieties that are resistant to those diseases when you buy plants. If they’re resistant they should have an “F” or “V” or both on the label.
Other wilts, though, are more troublesome. Bacterial wilt, in which the stem remains green but the inside turns black, and Southern wilt, in which the stem turns black a couple inches at the base, cause plants to collapse, Goforth says. Once infected there’s no way to control those diseases, he says. His advice: remove and destroy infected plants.
Nearby walnut trees are also bad news for tomato plants. A substance in the tree’s roots is toxic to tomato plants and causes them to wilt, The Pennsylvania State University Coop. Extension says.
One other wilt worth mentioning – the Tomato Spotted Wilt Virus – is carried by thrips, a small insect, says Brenda Gwynn, a horticulture agent in Lee County. It causes stunted growth and yellow leaf blotches, she says. No cure exists, so Gwenn advises pulling up infected plants and getting rid of them.
One way of fighting wilt and other diseases, extension agents say, is to rotate crops. That limits the possibility that diseases can build up in the soil. Their advice: allow several years before you replant tomatoes or family members like potatoes, eggplants and peppers in the same bed.
There are also fungal diseases such as Septoria leaf spot and Early blight which affect the tomato plant’s foliage, Gwynn says. Septoria’s circular spots with light center start on lower leaves and move up and Early blight, with lesions that look like targets, also start on lower leaves, she says.
While there are fungicides to combat both diseases, they are preventive and are of no use on infected plants, Gwynn says. Her advice: head off those problems before they start. She suggests not crowding plants, doing your watering in the morning, stopping overhead water and refraining from working with plants when leaves are wet.
Penn State’s extension service points out that rots often occur when tomatoes are lying on the ground. Soil and wet weather, it say, create a fertile environment for many kinds of rot. To avoid those problems, its says, prop plants to keep tomatoes off the ground and space plants far enough apart that leaves dry quickly.
Meredith Barkley gardens at home in Caswell County.