Gardening: Tomato growers, know thy enemies

By Master Gardener

If you’ve looked closely at tomato plant labels, you may have noticed a veritable alphabet next to the variety name: V, F, T, N and so forth. These abbreviations designate certain diseases or pests that the tomato is resistant to. How do you know if you need a plant with a particular disease resistance? Here’s a quick summary of those pesky viruses and diseases, their symptoms and whether there is a resistant tomato variety you should select.

• Verticillium wilt (V) is a fungal disease that lives in the soil. Signs include general wilting, yellow leaves, red or purple leaves and/or stems, distorted growth and early plant death. Resistant varieties are Big Daddy, Early Girl, Sungold and Yellow Pear.

• Fusarium wilt (F) is another soilborne fungal disease. Tomatoes infected with fusarium often show wilting on one side or even on individual branches. Dark brown discoloration of the main stem is common, and symptoms usually first appear when the fruit is sizing up. Tome, this is the meanest part of fusarium — just when you think you’re going to get a nice crop, everything heads south! Most varieties that are resistant to verticillium are also resistant to fusarium.

Letter codes on tomato plant labels — V, F, N and so on — denote resistance to certain diseases or pests. GETTY IMAGES

• Root knot nematodes (N) are only about one-hundredth of an inch long and pear-shaped. They live in the soil and infect roots, causing galls to form. The galls are easier to spot and can be up to an inch across (though usually smaller). These galls interfere with the roots’ nutrient and water uptake, so infected plants tend to wilt in hot weather. Celebrity, Better Boy, and Park’s Whopper are resistant.

• Tobacco mosaic virus (T) infects tomatoes, peppers, eggplants and tobacco through wounds. It causes weird mottling and splotchy discoloration in the leaves. The plant is stunted and has leaf curl, and the entire plant will turn yellow. If you smoke (tobacco), wash your hands thoroughly before working in the garden. Commercially grown tobacco is resistant to this virus but can carry it without showing symptoms. Most tomato varieties are resistant.

• Alternaria stem canker (A) is more common in coastal areas. It is a fungal disease that is both airborne and soilborne. Symptoms include an ugly brown or black lesion that consists of concentric rings, usually found near the base of the stem. These lesions can also be seen on the fruit or leaves. The fungus releases a toxin that eventually kill the plant. Roma, Celebrity and Yellow Pear are resistant.

• Tomato spotted wilt virus (TSWV) is a viral disease that is transmitted by thrips, which are tiny, sap-sucking insects. Young leaves will show some bronzing, followed by the appearance of round dead spots. Leaves will curl/cup downwards and some will eventually die back. Discolored rings appear on green fruit.

If you see signs of any of these infections, I recommend removing and disposing of the affected plant immediately. Do not compost, since these organisms often survive the composting process and can spread year to year.

Have questions?


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