Tomatoes Fungus…aka Irish Potato Famine Disease…aka Late Blight Fungus

August 03, 2009

I’m sure you’ve heard about the latest tomato problem…even Martha Stewart seems to be having problems with tomato fungus.

I’m sure you’ve heard about the latest tomato problem…even Martha Stewart seems to be having problems with tomato fungus. It’s called the Late Blight Fungus and is caused by Phytophthora infestans and affects tomato and potato plants worldwide. Farmers are diligent about preventing this disease through various methods, which includes destroying crops that are thought to be infected. Unfortunately the fungus is highly contagious and preventative methods do not always work. Late blight thrives in cooler wet and windy weather, exactly the conditions now plaguing the North East; in fact this is the earliest reported and most wide spread occurrence of the disease. Another unfortunate reality is that the infected plants were distributed by large local retail stores from Ohio to Maine. 

If you have a garden, be sure to inspect your plants daily! Symptoms include water soaked leaf lesions (when dry they appear lime green or even beige), white powdery spores, brown/black spots on stems and fruit and open lesions, each of which can produce hundreds of thousands of infectious spores.

There are some sprays available for home use - but are only effective before blight symptoms appear. Visit your local garden center for more information. Insects can carry the fungus spores, so spraying with both fungicide and insecticide are common practices for deterring pests.

Both conventional and organic farmers and home gardeners’ crops are susceptible to this disease and need to be equally diligent about inspecting, treating and disposing of their crops. Organic farmers and gardeners use a copper based fungicide, which is not as effective as conventional versions. Copper fungicides are easily washed off with rain and with the current weather conditions need to be reapplied often!

In general, organic fruits and vegetables are more susceptible to diseases and bacteria, because we don’t spray and spray with more potent chemicals…but many organic farmers take extra care to protect and monitor their plants. Our responsibility as consumers is to always practice proper handling-cleaning/rinsing/washing techniques regardless of organic or not!

Some have suggested that the “cure” for this blight would be irradiation. Not so! Tomatoes (and potatoes) infected with late blight cannot be effectively treated by irradiation. If the disease is already present, it will most likely have caused significant irreversible changes in the plants.

Irradiation (sometimes called - electron or cold pasteurization) is the process by which foods (meat, grains, fruits, vegetables, spices, seasonings etc.) after harvesting, during processing and before packaging are exposed to a controlled amount of radiant energy to kill harmful bacteria such as E.coli and Salmonella, prolong shelf life, reduce spoilage, and also inhibit ripening and sprouting. While this process may sound like the cure-all, critics are concerned. The amount of energy used is likened to 15 million times the amount of energy used in a single chest X-ray.  The energy waves passing through the food break molecular bonds in the DNA of bacteria, pathogens and insects. The process is FDA approved, and they report that this has little effect on the food itself and that the nutritional quality, taste, texture and appearance of the food are not compromised. Every package of food that has been irradiated must be labeled as such so that each of us can make the decision whether or not we want to consume such foods.