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Earth Resistance

Disease Resistant Tomatoes - How to Identify Them

Growing tomatoes isn't too difficult but they can be prone to disease. Don't despair though, as there are plenty of disease resistant varieties available but that in itself leads to another problem which is how to identify them.

Each variety is coded; e.g. "VF", "VFFA", "VFNT" but how on earth are we supposed to know what these acronyms mean? How do we tell which variety is resistant to which disease? That is where the coding comes in, which is fine if you know what each code means.

Below are the common designations, which should help you choose which variety of tomato plant is the one for you.

"A" means that the plant has resistance to the Alternaria alternata fungus which is a cause of Alternaria stem canker. The stems, leaves and fruit of the tomato are badly affected by cankers that vary in colour from dark brown to black. If the cankers are on the stem, there are often brownish streaks as well. Stem cankers can cause the death of a tomato plant before you can harvest the fruit.

"F" or "FF" indicates that the plants are resistant to the Fusarium oxysporum fungi which induce Fusarium wilt. This is a critical disease which causes the drooping and yellowing of the leaves beginning at the bottom of the tomato plant. Without treatment, Fusarium wilt can kill tomato plants well before the fruit can be picked. Some Fusarium fungi have become resistant themselves to the "F" resistance tomatoes, in which case, you need to choose plants with the "FF" coding.

"N" signifies that the plants are resistant to parasitic round worms, which often lie inactive in the earth. Effects of round worm infestation are root galls that are up to an inch in diameter. Afflicted plants are weak, do not react to fertilizer, and are inclined to droop when the weather is hot.

"St" specified tomatoes are not susceptible to grey leaf spot (Stemphylium). Affected tomatoes build up brown to black spots on older leaves. As the disease goes on, the spots become larger and the centres turn grey. The grey middles ultimately fall out, leaving behind small holes.

"T" indicates that the plants are resistant to the Tobacco Mosaic Virus. This results in a blotchy look to the leaves and smaller fruit and crop. Occasionally immature tomatoes will go brown.

"TSWV" points to resistance to the Tomato Spotted Wilt Virus. Signs of infection differ considerably dependent upon the variety of tomato, but consist of yellow and brown rings and brown streaks on tomato stems, leaves which have dead spots and tips, and seriously inferior growth. The tomatoes themselves may have red and orange discolorations when they are fully grown.

"V" means the tomato is not susceptible to the fungi which cause Verticillium wilt, Verticillium dahliae and V. albo-atrum. Signs of Verticillium wilt disease do not ordinarily become apparent until the plant is fruiting or it is not watered sufficiently. Signs include V-shaped gashes on the leaves.

Don't forget that disease resistant tomatoes are not necessarily immune to disease but if they do become infected, they are less likely to sustain as much damage as those varieties which are not disease resistant.

As well as choosing the right variety of disease resistant tomatoes, remember that changing where you plant your tomatoes can help prevent disease but be sure to rotate them with other plants which are not susceptible to the disease you are trying to eradicate.

Make sure that your tomato plants are well watered, are in well drained soil and are mulched to retain moisture. Spray with systemic insecticide or fungicide if you detect symptoms of disease (as long as you're not growing organic crops) and generally keep your tomato plants in as good a condition as possible.

Before planting your tomatoes, try to identify whether your garden already is home to any pests or diseases. Check the foliage and/or fruit of other plants in your garden and if you detect disease, take a sample to an expert to identify the cause. You will then be in a position to choose the right disease resistant tomatoes to plant.

By following sensible gardening practices, you will soon be able to eradicate the pests and diseases and end up with a bumper crop of tomatoes.

About the Author

Liz Canham Liz is a keen gardener who has exchanged the relative ease of gardening in Southern England for the trials of gardening on the Costa Blanca in Spain, where her garden is at a 45% angle on the side of a mountain. She is webmistress of
Gardening for All
.