Idaho growers concerned about crop heat stress

Published online: Jul 18, 2014
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Idaho farmers are worried prolonged above-normal temperatures may have stressed or damaged certain crops, especially onion fields already weakened by iris yellow spot virus and Russet Burbank potatoes.

According to the National Weather Service, temperatures for the first 14 days of July averaged 8.6 degrees above normal in Boise, where daily highs exceeded 100 degrees from July 11-14. Temperatures during the first two weeks of the month averaged 8.5 degrees above normal in Twin Falls, 6.2 degrees above normal in Burley, 5 degrees above normal in Pocatello and 4.7 degrees above normal in Idaho Falls.

Clint Shock, director of Oregon State University’s Malheur Experiment Station, said onion thrips transmitted a lot of iris yellow spot virus prior to the high temperatures.

“If the onions have water stress after they get iris yellow spot virus, our experience is it really hurts the yields,” Shock said. “Irrigation management is really critical.”

Complicating matters, Shock said, some onion growers in the upper region of the Owyhee Irrigation district, who don’t have supplemental Snake River water, are running out of water.

Rhett Summers, who raises Russet Burbanks on Eastern Idaho’s Rexburg Bench, said afternoon temperatures stayed at 85-90 degrees for three consecutive weeks.

“We’re concerned about plant stress and plant shutdown as the plant goes into survival mode instead of production mode,” Summers said. “We’re concerned about reduced yield and reduced quality.”

Randy Hardy, a fresh Russet Burbank grower in Oakley, said temperatures on his farm reached 101 on the afternoon of July 14. He’s been equally concerned about early morning temperatures in the 70s.

“What makes Idaho potatoes as good as they are is we have heat, but we don’t have extreme heat, and it cools off at night,” Hardy said.

He believes high temperatures may have taken the “edge off” a crop that had been about 10 days ahead of schedule and set a large number of tubers.

“You may see some fields coming down earlier than normal,” Hardy said, adding heat could contribute to rough skin, odd shape or high sugar levels at the ends of Burbanks.

Mountain Home grower Jeff Harper, whose farm reached 104 degrees on July 13, said he’s having trouble keeping up with irrigation demand, though he’s run his systems nonstop throughout the heatwave.

“Our irrigation systems were never designed to delver the water we need,” Harper said, adding he’s updated one farm to deliver 30 percent more water, and potatoes there seem to be weathering the heat better.

Despite the heat, Wilder, Idaho, grower Doug Gross expects average yields, noting plant canopies closed before temperatures spiked, shading soil. He said the Boise Project has an adequate water outlook, and he’s planted varieties that handle heat well.

“We got a great starts,” Gross said.

Idaho sugarbeet and corn growers say the heat has been good for their crops.

Hardy believes the heat has prematurely ripened some of his irrigated wheat. In North Idaho, Potlatch grower Joe Anderson said dryland winter wheat already affected by a cold winter is “turning pretty fast” in the heat, and he expects a thin spring wheat crop unless ample moisture arrives soon.