Potato farmers urged to watch out for 'late blight'

August 19, 2005

JOEL DAVIDSON/Frontiersman reporter

MAT-SU - Late blight, the devastating disease responsible for the Irish potato famine, appeared last week in Palmer and has now infected at least four different fields.

"It is fairly widespread in the Palmer area," said Larry DeVilbiss, director of the state Division of Agriculture. "Some fields just have a spot the size of a pickup, but others are completely taken over."

Caused by a water-mold micro-organism, the disease spreads rapidly through wind-borne spores, sometime traveling miles before landing on wet potato leaves. The fast-moving blight can create widespread damage if unchecked, and local disease and pest-control specialists are attempting to contain the recent outbreak.

DeVilbiss wouldn't reveal exact locations, citing a desire to maintain good working relationships with local growers. He did explain, however, that potato crops exposed to late blight are still edible if harvested soon enough, and pose no threat to human safety.

The disease, though, causes plants to quit growing and can drastically decrease overall crop yields if it spreads over an entire field. If the disease works its way from the leaves down into the actual potato (or tuber), it can cause problems with winter storage as well.

DeVilbiss said several farmers sprayed their fields with fungicides to halt the blight's expansion. At least one farmer, though, decided to harvest his whole field immediately rather than battle the disease.

Similar to the last time blight appeared, in 1998, this year's growing season is almost over, which bodes well for farmers who have potatoes large enough to harvest.

The 1998 incident also occurred in mid-August, but several farmers were still unable to harvest marketable-size potatoes. Overall, the majority of commercial potato fields were affected to some degree in the Mat-Su that year.

"If they are not marketable, you lose the whole crop," DeVilbiss said.

DeVilbiss said the fungicides are effective at protecting large crops. Likewise, gardeners and small-scale farmers who discover wet brown rot on leaves can respond by removing and burying potato vines.

Blight first appeared in Alaska in 1995, then again in 1998. But it hasn't shown up again until last week. On the two previous occasions, farmers responded effectively with multiple applications of fungicides on about a third of the crops.

About 840 acres of potatoes are under cultivation in Alaska, with the bulk of that in the Mat-Su. The state produces about 7,700 tons of potatoes a year.

Pam Compton, a pest management technician with the University of Alaska Cooperative Extension office in Palmer, said the conditions are perfect now for late blight to appear.

"It needs cool temperature and rain, and it needs an introduction," she explained. "It just so happens that it all hit that perfect balance."

Pinpointing the source of the current outbreak, however, is tricky.

"As Alaska becomes more cosmopolitan, a lot of new things can show up," Compton said. "It is very hard to trace down where it came from. Plants and seeds are not supposed to come into the state unless they are free of late blight. But that's not going to stop people from bringing up grandma's favorite potato plant."

Compton primarily works with smaller growers in identifying blight and other threats to garden plants. People may bring sample plants to the cooperative extension office in Palmer and she will test them for free. A free publication is also available with facts about the disease and information for the home gardener.

So far, only two samples have come in this week, both negative.

"If it is spreading, it is pretty indiscriminate," Compton said. "But we want to keep track of where it shows up."

In 1998, Compton tested more than 100 samples and found only one case of blight.

Late blight is widely recognized as one of the most devastating diseases to potato and tomato crops worldwide. It was responsible for the devastating Irish potato famine of the 1840s that led to the starvation of more than 100 people. Since the early 1990s, it has threatened crops in both the United States and Canada.

Contact Joel Davidson at

352-2266, or joel.davidson@ frontiersman.com.