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Howard Judelson's background
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The oomycetes
learn more about these exciting organisms

The late blight disease
learn more about the problems that P. infestans causes

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Late Blight

P. infestans is arguably the most important pathogen of the world's largest non-cereal crop, potato, and a significant tomato pathogen. The late blight diseases have always been important, but became especially difficult over the past decade. The worldwide cost of the potato disease alone exceeds $5 billion per year, including $1 billion spent on fungicides. This is enough to purchase potatoes to fulfill the caloric needs of the entire world for 2.7 days, based on 2200 Kcal/day and current U.S. potato prices!
potato famine
P. infestans caused the Irish potato famine in the mid-1800's, which led to the death of 1 million people. This historical picture--from the time of the famine--shows a woman and child trying to find some non-blighted potatoes to eat.

late blight on tomato

Late blight is not just a historical disease; it still causes devastating losses to agriculture in most years. In 2009, for example, a major epidemic attacked the east coast of the USA, causing major losses on both potato and tomato. On some tomato farms, losses approached 100%. Image: Tomato destroyed by late blight during the 2009 epidemic (B. Donaldson).

late blight on potato

Symptoms of late blight on potato leaflets and tuber. The white material in the center panel are the asexual spores.

infected potato in field

Infected potato plants (front right corner) in a field.
fungicide application

Fungicides are heavily used to control late blight. However, many of the fungicides may have adverse environmental effects. Their use is currently necessary, however, as it is estimated that losses due to late blight might reach up to 50% in the absence of fungicides.

For more information about late blight: UC IPM page

updated 8/2022