January 2017
Variety Increases Acreage in PNW By Bill Schaefer, contributing writer

With McDonald’s recently giving Pacific Northwest (PNW) process growers the green light to grow Clearwater Russet for french fry production, the variety promises to become a popular process cultivar in the coming years.

Clearwater Russet is a cross of the Bannock Russet and A89152-4, and was developed by the Tri-State Research and Breeding program. The Potato Variety Management Institute (PVMI) is the exclusive license holder and administers the commercial production of seed through license royalty payments for the Tri-State program.

The cultivar’s prominent characteristics include high U.S. #1 yields, low reducing sugars, uniform fry color and cold sweetening resistance, lower acrylamide forming potential and good processing quality out of storage.

Clearwater Russet

Jeff Stark, research professor of agronomy and director of the University of Idaho’s Potato Variety Development program, presented a set of management guidelines for the Clearwater Russet in Idaho at the Montana Potato Seed Seminar. The presentation included recommendations for Columbia Basin growers from Mark Pavek, Washington State University associate professor and research and Extension horticulturist.

Stark and Pavek believe that the combination of the longer growing seasons in the Columbia Basin and southwest and south-central Idaho, combined with the close proximity to fry processing plants, could make them the primary production areas for Clearwater Russet.

Their recommendations are similar but slightly different, due to the different climate and soil conditions between Idaho and the Columbia Basin.

Stark’s management recommendations for Idaho are:

Seed spacing of 12 to 13 inches.

Nitrogen recommendations (soil + nitrogen fertilizer) for Idaho:

  • 180-200 lb nitrogen/acre with 400 cwt/acre yield potential
  • 210-220 lb nitrogen/acre with 500 cwt/acre yield potential
  • 240-260 lb nitrogen/acre with 600 cwt/acre yield potential

Fifty percent applied by hilling, with remainder top-dressed or applied though sprinkler system.

Stark recommends that Idaho growers:

  • Use lower nitrogen application rates (~25 percent • Apply 50 percent nitrogen by row closure with remainder top-dressed or applied through the sprinkler system and minimize late-season nitrogen applications to promote skin set.
  • Irrigate to maintain 65 percent to 80 percent based on available soil moisture
  • Manage preharvest irrigations to achieve moderate tuber hydration levels at harvest to minimize shatter bruise
  • Use postharvest fungicide applications going into storage to reduce dry rot

Stark emphasized that these recommendations are general guidelines and that nitrogen fertilization rates and timings should be adjusted according to petiole nitrate levels to account for differences in available soil nitrogen. Research studies in Idaho have shown that the optimal ranges for petiole nitrate for Clearwater Russet are: tuber initiation – 20,000-22,000 ppm; mid-bulking – 16,000-18,000 ppm; and late bulking – 8,000-10,000 ppm.

For the Columbia Basin, Pavek said that in the in-row spacing trials he has conducted he has found that the majority of the time, if you space Clearwater Russet 1 inch wider than Russet Burbank, growers will achieve close to the optimum size profile for french fry contracts in the basin.

However, for the initial season he recommends that growers start out with the same in-row spacing as Russet Burbank.

“If they (growers) don’t like the size profile after that season, they’ll still do fine, but if they think they need to get a little larger size profile then I would space it out one more inch the next year,” Pavek said. “They can keep going that direction but I don’t recommend they go wider than 12 inches. I wouldn’t go above 12 inches wide in the Columbia Basin.”

For now, Pavek recommends fertilizing similar to Russet Burbank or Ranger Russet; however, he recommends keeping Nitrogen below 375 pounds per acre. Somewhere between 350 and 375 pounds of nitrogen across the season is ideal, he said. That includes a soil test and you subtract that from the total.

Two-thirds of the nitrogen should be applied through irrigation water and complete nitrogen applications by the end of July.

“You want those vines to mature as much as possible, and if you keep pumping nitrogen into this variety into August you’re going to have a problem with it maturing and you may have a problem with shatter bruise,” Pavek said.

Pavek said that it’s important to get a mature plant to avoid shatter bruise, which can lead to fusarium dry rot.

“Let them dry out a bit, don’t overwater them towards the end,” he said. “And again, cut nitrogen off by the end of July in the Columbia Basin.”

Storage management

Storage recommendations for Clearwater Russet were put together by Stark, Tina Brandt and Nora Olsen, from the University of Idaho’s Kimberly Research and Extension Center; Rich Nowy and Jonathan Whitworth from the University of Idaho’s Aberdeen Research and Extension Center and USDA’s Agricultural Research Service Aberdeen office.

Harvest conditions

Clearwater Russet has a higher susceptibility to fusarium dry rot than Russet Burbank. Bruising and wounding should be minimized during harvest and handling in order to lessen this disease in storage.

Glucose concentrations at harvest (seven days postharvest) in Clearwater Russet were significantly lower than Russet Burbank. Three-year average glucose concentration fresh weight for Clearwater Russet was 0.025 percent. Three-year average glucose concentration fresh weight (FW) in Russet Burbank was 0.059 percent.

Glucose concentrations during storage

In three years of testing, glucose concentrations continued to be significantly lower than Russet Burbank at all three storage temperatures during the nine-month storage season.

Stored at 48 ̊ F, glucose concentrations in Clearwater Russet remained at or below 0.04 percent FW; Russet Burbank’saveragewas0.10percentFW. Stored at 45 ̊ F, glucose concentrations of Clearwater Russet remained at or below 0.05 percent, while Russet Burbank’s were higher and peaked at 0.16 percent FW. Stored at 42 ̊ F, glucose concentrations of Clearwater Russet remained below 0.10 percent FW. These low glucose concentrations indicate that Clearwater Russet
has cold-induced sweetening resistance; it can be stored at cooler temperatures and still be used to make premium processed products.

  • Cure at 55 ̊ F and 95 percent relative humidity for 14 days.
  • Storage: Maintain 95 percent relative throughout storage
  • Frozen processing: While Clearwater displayed acceptable processing from 42 ̊ F, holding tuber at 45 ̊ F or above will minimize fry mottling.
  •  Fresh market and dehydration processing: Hold at 42 ̊ F.

Sprout inhibition

Apply CIPC before dormancy break but after curing.

  • 42 ̊ F. Apply CIPC between two and 15 weeks after harvest.
  • 45 ̊ F. Apply CIPC between two and 13 weeks after harvest.
  • 48 ̊ F. Apply CIPC between two and 12 weeks after harvest.

In the absence of sprout inhibitors, dormancy length for Clearwater Russet is 55 to 65 days shorter than that of the Russet Burbank.

  • Variety 42 ̊ F 45 ̊ F 48 ̊ F.
  • Russet Burbank 175 days 155 days 130 days
  • Clearwater Russet 110 days 90 days 85 days

It is important to apply early if the intended storage duration is longer than the indicated dormancy length.

Storage duration

High processing quality persists throughout 36 weeks after harvest at 42 ̊ F, 45 ̊ F and 45 ̊ F.

Fry mottling

Only slight mottling has been observed in Clearwater Russet and only at 42 ̊ F storage; at 45 ̊ F and 48 ̊ F, mottling was seldom observed.

For more information about Clearwater Russet, visit pvmi.org or call Jeanne Debons, PVMI executive director, at 541-318-1485.





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