Plants require high humidity, warm temperatures

By MITCH LIES

Capital Press

HERMISTON, Ore. -- Judging from two years of trials, sweet potatoes could be an up-and-coming crop for Columbia Basin growers.

The crop, which is not a yam and not a potato, did surprisingly well in trials near Pasco, Wash., in 2011 and 2012. And with demand for sweet potato french fries increasing, don't be surprised if the crop catches hold here.

In a presentation at the Hermiston Farm Fair Nov. 29, Washington State University Extension entomologist Tim Waters said the crop produced yields comparable to those in Louisiana and California, the top two sweet potato-producing states.

Because few broadleaf herbicides are registered for the crop, and because sweet potatoes need high humidity to excel, sweet potatoes aren't a slam dunk for Northwest growers.

But, given enough water and heat units, it is apparent they could be a viable crop here.

"There certainly is demand," Oregon State University Extension agent Don Horneck said.

Horneck said Lamb Weston recently built a multimillion-dollar plant in Louisiana strictly to process sweet potatoes.

Processing lines here are capable of handling the crop, he said.

Columbia Basin growers have tried to produce sweet potatoes in the recent past, Horneck said. But, he said: "I haven't seen yields like this before."

In two years of trials near Pasco, Waters said he was getting upward of 15 tons to an acre in well-irrigated sites.

The key, he said, is to get plants established in warm soils.

"After plants got established and started growing, they really grew fast," Waters said.

In one instance, at high irrigation levels, the crop yielded 24.5 tons to an acre, well above yields in Louisiana and California. Yields fell to as low as 5 tons to an acre in plots that received minimal water, Waters said.

"If you do grow sweet potatoes, don't let them get dry," Waters said.

Horneck estimated growers need to average 15 tons an acre or more to generate a profit.

Waters, who tried growing sweet potatoes near Moses Lake, Wash., said the warmer sandy soils near Pasco produced far better yields.

The key, he said, is the Pasco soils warmed much earlier than the Moses Lake soils.

Also, he said, pushing back harvest dates appeared to boost yields.

"The later you can push the harvest, as long as you have warm weather, the yields keep going up," Waters said.

Sweet potatoes were for decades produced and sold in the Columbia Basin, primarily in Franklin and Benton counties, Waters said. A labor shortage triggered by World War II ended the crop's run in the basin.