Blight fight a losing battle

Aug. 23, 2005

JOEL DAVIDSON\Frontiersman reporter

PALMER - The recent outbreak of late blight disease has now infected at least five Palmer area potato fields and appears resistant to current eradication efforts.

Larry DeVilbiss, director of the Alaska Division of Agriculture, said the outbreak is worse than the only other recorded blight outbreaks in 1995 and 1998.

"This is more serious than anything I saw in 1998," he said Monday. "At least one grower has lost everything."

Attempts to treat fields through spraying fungicide have so far proved unsuccessful, according to DeVilbiss.

"It seems unresponsive to spraying," he said. "We are still checking on it, but we think it is a more virulent strain."

Late blight is infamous for causing the Irish Potato Famine of the 1840s, when more than 1 million people died of starvation. While the disease poses no direct threat to humans, it can decimate whole fields within days.

Caused by a water-mold micro-organism, the disease spreads rapidly through wind-born spores, sometimes traveling miles before landing on wet potato leaves. Once the leaves are infected, plants quit growing, which drastically decreases overall crop yields.

At least two Mat-Su farmers have harvested their fields early, rather than risk a losing battle to the blight. DeVilbiss said those farmers probably lost up to 50 percent of their crop by harvesting during the peak growing period.

Some farmers, though, would rather harvest less now than risk having blight work its way down into the actual potatoes (or tubers), where it can cause problems with winter storage.

Both home gardens and commercial fields are being examined this week in an effort to contain the disease and pinpoint its source. So far, all home growers are blight-free, but DeVilbiss said the source is still a mystery.

Blight first appeared in Alaska in 1995 and then again in 1998, but hadn'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.

The potato blight quarantine of 1998, which requires that all potato plants and seeds be blight-free before entering the state, is still in effect, DeVilbiss said. Blight can spread by the transportation of contaminated plants from other areas. Once the blight lands in the state, wind and rainy weather cause it to proliferate.

DeVilbiss recommended that both home and commercial growers check their potato plants regularly. About 840 acres of potatoes are currently under cultivation in Alaska, with the bulk of that in the Mat-Su. The state produces about 7,700 tons of potatoes a year.

"If they see or suspect spots on their leaves, they should pull the leaves off and bury them," he advised home growers, adding, that leaves left on the ground could contain spores that spread through the wind.

DeVilbiss advised commercial farmers to beat potato vines and leaves down at least five days before mechanical harvesting. Without a living plant, the spores will die, thereby decreasing chances of blight infecting the underground potatoes.

Late blight is widely recognized as one of the most devastating diseases to potato crops worldwide. It has threatened crops in both the United States and Canada.

State university and government pest-management officials are continuing to monitor Palmer fields for further blight infection. Information and publications about late blight are available online through the UAF Cooperative Extension Service Web site at www.uaf.edu/ces/ or at the local extension office in Palmer. For more information people may also call the Palmer office at 745-3360.

Contact Joel Davidson at

352-2266, or joel.davidson@

frontiersman.com.