Early Idaho Frosts Take Bite out of Potato Harvest

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Recent freezing temperatures in Idaho set back the top potato-producing state’s harvest, but it could be weeks before the extent of the damage to the crop is known.

In an effort to quantify the impact of the cold snap on Idaho’s potatoes, Gro analyzed more than three decades of weather patterns in Bingham County, the state’s largest producing region. Our analysis estimated that potato yields in the county were reduced by 3% from their 10-year trend. It also estimated that about 2% of planted acres could be abandoned because of frost damage.

The cold hit Idaho and other parts of the northern United States in early October. Freezing temperatures and record snowfall took a substantial toll on crops grown throughout the northern Plains and northwest regions. Multiple frost events caused widespread damage to Idaho’s potatoes.

Idaho has long been the nation’s leader in potatoes. In 2018, Idaho’s potato output was 141.75 million hundredweight, or about 30% of total US production, according to data from USDA NASS. Bingham County, which is located in the southeast part of the state and was directly affected by the frost, accounted for 18% of the state’s output; the county produced 25.7 million hundredweight in 2018.

This chart shows annual potato production for the US (purple line) and the five top producing states (stacked bars). Idaho has been the largest potato producer for more than half a century. 

Frost damage can affect potatoes in a few different ways. Extended cold can lower pulp temperatures and dramatically increase the risk of shatter and blackspot bruising. Potatoes harmed by frost have a greater likelihood of developing soft rot. Frozen soil can prevent harvest altogether.

On the ground crop condition surveys, published weekly by NASS, reported widespread losses for this year’s crop. Some fields were left unharvested because frozen potatoes were too costly to dig up. In other cases, the quality of harvested potatoes was degraded so much that the potatoes had to be discarded.

To estimate the frost’s impact on Bingham County potato yields, we first created a daily temperature index. For this calculation, we took an average of the minimum observed temperatures at the six GHCN weather stations located in Bingham County for the last 40 years. GHCN, or Global Historical Climatology Network, is an integrated database run by NOAA of climate summaries from land surface stations across the globe. GHCN data is included in the Gro platform.

This chart shows daily minimum observed temperatures at a weather station in Blackfoot, Idaho, located in Bingham County. In Blackfoot and other key potato-producing areas, temperatures dropped below freezing multiple times in the first half of October. The latest year is shown as a line with markers. For comparison, other lines represent previous years. 

We found five analogous years when Bingham County also experienced below-freezing temperatures for consecutive days prior to the completion of potato harvest. These were 1985, 1986, 1990, 2002, and 2008. In those five years, potato yields in Bingham County ranged from 1% to 8% below trend based on the prior 10 years, with an average decline of 3%. The USDA will first estimate 2019 national and state level potato yields in its Nov. 8 Crop Production report. Official county-level yields for 2019 aren’t released until next year.

While yield decline measures account for damaged crops, they don’t take into account acres that farmers decide not to harvest because of the frost damage. For the five previous analogous years that we surveyed, farmers abandoned 2% of their planted acreage on average.

Potato production volume can be difficult to estimate, in part because acres planted in Idaho vary widely from year to year. Local reports in Idaho suggest some potato farmers expect to have lost about 10% of their crop because of the recent freeze. Among the more pessimistic forecasts, a representative of the Idaho Potato Commission estimated that 30% of the potato crop statewide was lost to frost damage.

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