Weather conditions can bring blight


by William J. Langenberg, M.Sc. Env. Bil.

The Late Blight-causing fungus, Phytophthora infestans, proliferates during weather conditions we are experiencing this year. This Summer is bringing us much heat during the day and cooler temperatures at night. The hot days, followed by the cooler night temperatures, result in fog formation during the early morning hours. This fog formation, and related high humidity, are the environmental conditions that are favourable for the causal agent of Late Blight on potatoes and tomatoes to proliferate.

Here a picture of diseased stems and leaves. Pay attention to the blackening of the stems, which I removed from my own garden.

Phythophthora was responsible for the “Great Potato Famine” in Ireland during the 1840s, which resulted in a million deaths due to starvation. The Irish potato famine caused the subsequent migration of Irish people to North America.

About a decade ago, scientists discovered that the fungus Phythphthora originates from Mexico, and not the Andes, as was originally thought. To prevent severe outbreaks and the spread of this dreadful disease in the backyard garden: do not water with overhead sprinklers. Do not walk through, or work in, the garden when the leaves are wet. Remove all diseased stems and leaves from the garden and do not compost them. In the old days, we would burn the diseased foliage. Today, they go in the garbage.


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