Gone Gardenin' - Blighty! Wilt, fungus and rot lay siege to the poor tomato

ALBERT PARSONS/FOR THE SUN Enlarge Image

Catfacing produces bulges and deformities on the blossom end of the fruits.

Last week I discussed my tomato crop, how I go about growing my tomatoes, the varieties that I grow, and so on.

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These tomatoes have suffered from early blight; they have a hard core that will remain even after the fruit is ripe. (ALBERT PARSONS/FOR THE SUN)

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A healthy tomato plant has unblemished, dark green foliage. (ALBERT PARSONS/FOR THE SUN)

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The foliage of this tomato plant is gradually succumbing to disease. (ALBERT PARSONS/FOR THE SUN)

Quite a number of my readers have called me about tomato diseases this year, so perhaps it is time to discuss the most common tomato diseases and how to prevent them — or at least how we can minimize the damage they do to the tomato crop.

The tomatoes in our garden have had a lot of cracking on them this year — particularly the ones that we picked first. This disease is the result of rapid growth and too much fluctuation in moisture levels. The cracks can radiate out from the stem on the top of the fruit or develop in concentric circles around the stem.

Although the cracks are unsightly, they do not render the fruit inedible, and after the damaged portions are cut off, the fruit can used as usual.

Catfacing, a form of cracking that occurs at the blossom end and involves distortions and bulges, was also prevalent on the early fruits we picked.

This phenomenon is caused by cold weather at the time of blossoming; some tissue is killed which produces misshapen fruits with lots of bulges and crevices. The symptoms are usually only on those fruits that developed at the particular time the weather was cold; the rest of the fruit on the plant will be unaffected.

Another tomato disease that I have heard a lot about this year, blossom end rot, is exacerbated by wide fluctuations in moisture levels during the growing season. Many gardeners mulch their tomatoes to ensure a more even moisture supply.

The fruit develops rot at the blossom end and eventually the fruit rots. Too much nitrogen in the soil will increase the chances of blossom end rot occurring; therefore it is not advisable to use a high-nitrogen fertilizer on tomatoes.

The disease is also encouraged by a lack of calcium in the soil; adding bone meal or crushed eggshells to the planting holes in the spring will help to prevent the disease by increasing the available calcium. Rotted fruit should be removed from the garden and discarded, not put into the compost bin.

Two wilt diseases that attack tomato plants are fusarium wilt and verticillium wilt. In both cases, the main symptom is that the leaves turn yellow and then turn brown and dry off.

During the day, the plants may look wilted but they appear to recover at night. Eventually the entire plant will die, although the fruit, if picked early enough, is often useable. These diseases most often develop during cool weather.

The best preventative measure against wilt diseases is to use resistant varieties. The capital letters V and F will appear after the variety name on the plant tag or in the seed catalogue of varieties that are resistance to these wilt diseases.

Yet another disease, septoria leaf-spot, is quite common in tomatoes. This is a fungal disease that causes paper-like patches to develop on the leaves and then tiny dark specks appear on the patches — these tiny black spots are the tell-tale symptom of the disease.

A fungicide can be used to combat leaf-spot, as it can to prevent other fungal diseases, which are considered the most serious of the tomato diseases.

And the most serious fungal disease by far is late blight, which develops very quickly and without fail destroys the crop. Greyish looking irregularly shaped patches on the leaves spread rapidly and sometimes a whitish mould is also present.

The grey patches become dry and papery and very noticeable black areas develop on the stems. There is no cure for late blight, but a regular spray program using a copper-based fungicide before the disease organisms are present will keep the disease at bay.

The organism that causes late blight does not usually live over winter in our cold climate, but good hygiene is advised. Practising good hygiene by cleaning every scrap of tomato foliage off the garden in the fall is vital in preventing the development of another blight called early blight.

Early blight, also caused by a fungus, can over winter in the soil. Therefore removing old foliage from the garden in the fall is important. A copper-based fungicide will prevent the disease.

The symptoms of early blight include dark spots on the leaves that have concentric rings around them. The older leaves are the first to exhibit symptoms by turning yellow and then dying.

The prevalence of many tomato diseases is often dependent on weather conditions — too much rain, cool temperatures, extended dry spells followed by heavy rainfall will all contribute to a high incidence of disease. The fungal diseases will develop more often during wet weather, or when the humidity is high.

After looking at the list diseases that attack tomatoes — and I haven’t mentioned them all! — it is a wonder that we are able to grow tomatoes at all.

The tomato is, however, a tough and resilient plant and with a bit of encouragement from us gardeners, and by taking a few precautionary measures, we can harvest a bumper crop of home-grown tomatoes.

Albert Parsons is a consultant for garden design and landscaping who lives in Minnedosa.

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Republished from the Brandon Sun print edition September 20, 2012