Tomato Late Blight

Potentially devastating to the home gardener, late blight can wipe out an entire tomato crop, and all the hard work that went into it, in a few short weeks. Moreover, adding insult to injury, late blight can also affect peppers, potatoes, and eggplant.

Causes and Symptoms

Late blight (Phytophthora infestans) is a fungus-like microorganism that is usually brought into the garden by the introduction of infected tomato seedlings or seed potatoes or by infected volunteer plants from the previous year’s garden. The fungus is also spread atmospherically when the live spores are blown in during periods of rain and wind. Optimum conditions for the rapid spread of the disease occurs during episodes of moderate temperatures and high moisture.

Identification of late blight on tomato plants is done by inspection of the fruit and foliage and will initially appear as gray areas on the leaves. These areas will then spread and a mold will develop on the lower surfaces of the leaves. Brown spots on the plant stems, as well as the loss of foliage, are also indications of late blight. If the weather conditions are favorable (moist), the spread will be rapid.

Treatments and Control

The first line of attack against late blight is for immediate removal and destruction of any infected plants. The plants should then be either burned or bagged and discarded through normal garbage disposal means. Infected plants should never be placed in the compost pile as this will certainly spread the disease.

Staking tomatoes and using a system of drip irrigation will reduce the potential for leaf dampness, as will allowing enough space between plants for adequate air circulation. Mulching the area around the plants is also beneficial. In addition, you can plant tomato disease resistant varieties that are specified as blight resistant.

If the infestation is not too widespread and perhaps only affecting a few plants, removing and destroying the infected plants and treating the remaining healthy ones with a fungicide spray for tomatoes may salvage some of the crop. Tomato fungicides containing copper are often recommended for the gardener wishing to avoid harsh chemicals.

Any fungicide treatments applied are likely to be successful only if the plant or plants are not showing any signs of late blight infestation. Frequent and regular applications are generally recommended with particular attention being made to spray the plants after each rainfall.

It is important the gardener rotate their tomato plantings and not plant tomatoes in the same spot every year, perhaps leaving two to three years between planting tomatoes in the same location.

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