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Wildfires happen every year in the Idaho mountains. In turn, smoke settles down into the Treasure Valley, often prompting unhealthy air quality warnings.
Potato growers in the area have noticed that their yields were off and stored potatoes had more disease in bad smoke years. Similarly, McCain Foods found that French fries made in these years were a darker color than desired.
Smoky years tend to be very hot and dry, but what was causing the yield and quality decline: the environment or the smoke?
In 2022, Mike Thornton and his team at the University of Idaho designed experiments to find out. After analyzing the results on fresh tubers and those coming out of storage, the researchers found smoke had very little impact on the potatoes that they induced for three hours a day with extreme levels of smoke. There was no weight loss on the smoke-induced versus the control spuds and little impact on storability. The team could not document the losses that the industry was seeing with their experiments.
What they did see was a loss in quality in the smoke potatoes, with a 2-3% decrease in No. 1s, which could affect returns. And if growing for processing, there are incentives for size and disincentives for culls, which could also impact the bottom line.
“Smoke exposure is reducing the quality output of potatoes,” Thornton said at the 65th meeting of the Idaho and Malheur County onion growers’ associations.
And in addressing the bottom line, Thornton said potatoes take longer to mature in smoke years, forcing growers to water and fertilize longer. In addition, more water could lead to more storage decay, further dropping returns.
How Potatoes Relate to Onions
The smoke experiments were only done on spuds, but Thornton looked at historical data of smoke levels and onion production. Comparing four bad smoke years to four light smoke years in the Treasure Valley, he found that overall onion production seems to go down in heavy smoke years.
What This Means to Onion Growers’ Bottom Line
In the light smoke year of 2019, the area produced 20.5 million cwt of onions. About 80% of those were jumbo size or larger, totaling about 16.4 million cwt of jumbo onions. Assuming a 3% drop in a heavy smoke year, 77% of onions would be jumbos or larger, totaling 15.8 million cwt. This represents 616,000 fewer sacks of jumbo and larger onions in a heavy smoke year. With numbers like these, Thornton thinks heavy smoke years could have a significant impact on return.
