This summer's unusually high temperatures are damaging Idaho's potato crop, but University of Idaho potato specialists say the extent of the damage is impossible to determine.

"There are heat-stress problems in some fields from western Idaho to Blackfoot, and the yield potential in those fields has been reduced by up to 25 percent," said Dr. Gale Kleinkopf, a potato physiologist.Kleinkopf said some areas, which have not experienced the heat, should see normal yields.

Heat damage to potato tubers affects both appearance and processing quality, and Kleinkopf said once the damage occurs, it is irreversible.

He said that in fields affected by heat stress, 55 percent to 60 percent of the potatoes may make U.S. No. 1, while in an average year the percentage is 65 percent to 70 percent.

In addition, the heat has made some fields more susceptible to disease, Kleinkopf said.

U. of I. extension specialist Gary Beaver said about one fourth to one third of the fields in the Treasure Valley are affected by heat stress.

"The thing that seems to separate (the undamaged fields) from the ones that are heat-stressed is the planting date and irrigation practices," Beaver said.

Fields that were planted earlier and received more frequent irrigation received almost no damage, he said.

However, overall production in Idaho should equal last year's, Kleinkopf said.