Tomato Late Blight

This fast-spreading disease is found in both potato and tomato plants, and is the same plant virus that caused the infamous potato famine in Ireland in the 1800s (the disease destroyed the potato crops for several successive years). Late blight, named so for it appearing late in the growing season, is caused by a fungus that survives from one season to the next in infected plants. It attacks both the leaves and the fruit of the tomato plant, causing eventual death to the plant.

The blight is not dangerous to people, however tomato farmers and large-scale growers are at risk of having their entire crops destroyed, as the spores of the blight can travel up to 30 miles on the wind. If the blight is not contained, a shortage in tomato crops will inevitably lead to an increase in price at the grocery store.

According to the Cornell University College of Agriculture and Life Sciences typical signs of blight are large brown spots on the leaves, about the size of a nickel. Spots or growths (lesions) may also appear on the stems. There may also be a white fungal growth on the leaves and eventually, the fruit themselves will develop brown spots.

A large-scale tomato grower who supplies chain stores with tomatoes, such as Lowe’s, Home Depot and Wal-Mart, may be the source of the blight, according to a July 3rd article by the Associated Press. Plants purchased from these stores should definitely be watched closely and checked often for any signs of the blight.

Should a tomato plant show signs of late blight, it must be destroyed. Fungicides and pesticides will not make the plant ‚”well” again. To control the spread of the spores and minimize any more damage, wrap the affected plant in a large garbage bag and remove the plant, roots and all. Since this is a diseased plant, it should not be composted but put directly in to the trash.

Prevention Tips

To help prevent blight:

• Frequently check tomato vines, foliage and fruit for any signs of spores and rot.
• Get any tomato vines off the ground and make sure they are upright, and properly caged.
• Avoid crowding in too many plants together, allowing about 1-foot between each plant.
• Don’t overwater the plants, as dampness and humidity are perfect breeding grounds for the spores, preferably watering only at the base of the plant and not overhead.
• Lastly, a good quality compost to cover the ground base is better than mulch.