Although few foods top the luscious taste of a vine-ripened tomato picked from your own garden, losing tomato fruits or entire plants to disease can be extremely disappointing. Choosing varieties of tomato plants (Solanum lycopersicum) that are resistant to diseases called "early blight" and "late blight" can help to ensure you harvest lots of tasty, unblemished tomatoes from your home garden. Tomatoes are frost-tender plants that are grown as annuals in all U.S. Department of Agriculture plant hardiness zones.
Blight is a fungal disease that develops during cool or wet weather, when conditions favor growth of the microorganisms. In tomatoes, two separate diseases called early blight and late blight may cause serious problems. Early blight is more common, usually developing just as the first small fruits appear on a tomato plant. Initially, it causes dark spots on leaves and eventually results in browning of stems and fruits. Early blight ultimately can kill the entire plant. Late blight generally appears later in summer while fruits are ripening. It causes gray spots on leaves and wet, dark spots on tomatoes, which can make the tomatoes inedible. Like early blight, late blight also can cause an entire plant to die.
Several tomato cultivars that produce large, red tomatoes have good resistance to early blight and late blight. The variety "Defiant" is an example, producing 6- to 8-ounce tomatoes with what is considered good taste and substance. It is moderately resistant to early blight and extremely resistant to late blight. Another variety, called "Legend," is a heavy producer that develops big tomatoes sometimes exceeding 1 pound in weight. It is quite resistant to both early and late blight, and it does very well under cool, damp conditions. Both "Defiant" and "Legend" are determinate plants that set terminal buds and stop growing once vines reach about 3 feet in height.
Tomato varieties that developed naturally and have been in existence for many years are called heirlooms. Several of these plants have good to superior resistance to blight. The variety "Black Plum," which is a mahogany-skinned, small oval or plum type, has especially good resistance to both blight diseases. "Black Plum" is an indeterminate type of plant with vines that continue growing in length during the entire season. Several other heirloom tomatoes have good to moderate resistance to early and late blight. These include "Black Krim," which produces large, beefsteak-type tomatoes that are mahogany in color, and "Aunt Ginny's Purple," which has large, purplish-skinned tomatoes that can reach 1 pound in weight. Both of these varieties are also indeterminate in their growth habit.
Tomatoes come in many shapes and sizes, including small types called grape or cherry tomatoes and odd-shaped tomatoes that resemble pears. Several of these specialty type varieties have good to excellent resistance to both early and late blight. Among the grape or cherry types, "Red Currant," with 3/8-inch, sweet fruit, has good resistance while "Matt's Wild Cherry, which produces clusters of 1-inch tomatoes, has excellent resistance to both diseases. Two yellow tomatoes, a cherry-type called "Yellow Currant" and one called "Yellow Pear" that has 1-ounce, pear-shaped fruits, also display excellent early and late blight resistance. All of these small-fruited varieties are indeterminate in their growth habit.
- University of Illinois Extension: Tomato
- Organic Gardening: How to Grow Tomatoes
- Rutgers University: Table of Late Blight- and Early Blight-Resisant Tomato Cultivars for Home Garden
- Cornell University: Late Blight-Resistant Tomato Varieties
- Oregon State University Extension Service: "Legend" Tomato is Big, Early and Late Blight-Resistant
- Johnny's Selected Seeds: Defiant PhR (F1)
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