Published online: Aug 31, 2009
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MANHATTAN, Kansas-It's no wonder Americans are worried that a fungus-like organism called Phytophthora infestans has shown up this year, affecting tomatoes and potatoes in the Northeast.

The organism causes a disease called late blight. And it's a big reason why so many Americans now have Irish branches on their family tree. The fast-spreading, devastating blight caused the "Irish potato famine" of the 1840s, which drove almost 1 million poor immigrants to U.S. shores.

"Since this year's outbreak hit the national news, our Plant Disease Diagnostic Lab has been getting numerous calls from concerned Kansans. We're keeping our eyes open. The fact is, though, late blight is extremely rare here because our summers are generally too hot and dry," said Megan Kennelly, plant pathologist with Kansas State University Research and Extension.

The disease organism thrives in weather conditions similar to those that keep Ireland so green.

Parts of Kansas have been wet this year, too, but nowhere near 2009's moisture to-date in the Northeast. Kansas also has had some growing season days with unusually mild temperatures. Even so, late blight thrives at 60 to 80 degrees, and the state has already been much hotter than that, Kennelly said.

In favorable weather, the organism produces so many wind- and water-borne spores that it can infect and kill a potato field within days. In the 1800s, it spread Ireland-wide during a single harvest season.

But, today's U.S. Northeast growers have faced major outbreaks before in both the 1990s and early 2000s. So, they know what to scout for and what's available to protect their crops, Kennelly said.

The affected region's university Extension specialists and state departments of agriculture are scouting and pulling infected plants off retail shelves, she said. Local Extension agents are helping home gardeners diagnose and destroy infected plants to help prevent the disease's spread.

Massachusetts is maintaining a state-university website about late blight (