Submitted by University of Idaho
PARMA, Idaho — A University of Idaho researcher believes hot early season weather in 2013 contributed to a substantial increase in potatoes with excessive sugar concentrations at their stem ends.
Mike Thornton, superintendent of the University of Idaho’s Parma Research and Extension Center, fears stress due to rationing of a tight water supply could also exacerbate the condition, commonly called sugar ends, in this season’s crop.
French fries cook too dark where sugar levels are elevated, costing processors and growers millions per year. Sugar ends are most prevalent in western Idaho, where temperatures tend to be higher.
Thornton said processors are finding their 2013 crop has more sugar ends than normal.
“Processors are telling me there is some incidence even in eastern Idaho,” Thornton said. “I think that’s due to unusually warm temperatures, particularly unusually warm night temperatures, experienced in mid-July last year.”
In university research plots in Aberdeen, Idaho, about 31 percent of Russet Burbanks had sugar ends in both 2011 and 2012, compared with 50 percent in 2013. Thornton emphasized researchers grade spuds more strictly than industry.
Under ideal conditions, potato plants derive sufficient energy from photosynthesis and build starch in tubers to generate new plants the next season. When stressed by heat or lack of water, plants seek energy from the tuber, mostly by the stem end where cell division remains active. Once starch is converted into sugar, the damage can’t be undone.
Thornton advises growers against skimping on water during the critical period of cell division, lasting nine to 11 weeks after planting. When tubers are about egg-sized, plants switch to adding bulk to existing cells and are less vulnerable.
“Many of these irrigation districts are warning about limited supplies of water,” Thornton said. “Some growers will probably try to stretch out that water as much as they can so they don’t lose yield.”
Thornton said Russet Burbank is especially prone to sugar ends. Processors are evaluating resistant varieties such as Clearwater Russet, Alpine Russet or Classic Russet.
Thornton said growers may also minimize sugar ends by: narrowing rows from 36 inches to 34 inches to cool soil with a tighter canopy, avoiding soil compaction and avoiding root damage by using Dammer Dikers only prior to plant emergence.
Wilder, Idaho, grower Doug Gross agreed sugar ends were especially bad in 2013, particularly in fields with white soil or where he experienced early season irrigation problems. In white soil, Gross adds a water penetrant to reduce plant stress.
“The first most critical thing is early season irrigation,” Gross said.
In 2012, Burley grower Craig Larson fed 80,000 sacks of potatoes to cattle due to sugar ends. Last season, he bought more wheel lines to irrigate on a five-day rotation rather than a six- or seven-day cycle. He also added larger spray nozzles and increased the watering capacity of his pivots. His sugar-end problem was much less in 2013.
“It cost me quite a bit of money, but if I would have repeated in 2013 what I did in 2012, it would have hurt bad,” Larson said.