Spud yield losses caused by potato virus Y cost Idaho’s economy about $34 million per year, according to results of a recently completed economic impact study by University of Idaho agricultural economist Chris McIntosh.
The estimate includes $6.5 million in lost wages from 184 Idaho jobs that would otherwise be filled if not for PVY.
McIntosh estimates direct losses to Idaho’s economy caused by PVY at $19.5 million, and indirect losses at $14.5 million.
He estimated Idaho’s annual yield loss to PVY, after shrinkage, is 2.3 million hundredweight. Prices used for his calculations are based on a five-year average. For simplicity, he made no allowance that having more potatoes impacts price.
In Russet Norkotah, McIntosh found every 1 percent of PVY in seed reduced yields by 1.17 hundredweight per acre, causing a mean fresh-market loss of $12.27. Russet Burbank yields dropped comparably, with a mean fresh-market loss per acre of $11.59 and a mean processed market loss of $9.17 per acre.
His study was funded with $50,000, covering five years of research, from the USDA’s Specialty Crop Research Initiative. McIntosh assigned a graduate student, Giri Raj Aryal, to the project.
His yield data comes from UI Extension seed potato pathologist Phil Nolte’s trial plots planted in commercial fields for the past five years on the Rexburg Bench. Nolte’s plots received federal, Idaho Potato Commission and UI funding.
Nolte purchased spuds from fields confirmed by Idaho Crop Improvement Association to have about 10 percent PVY. He tested the seed and then blended clean and infected seed to PVY concentrations ranging from 2 to 50 percent for planting.
He’s found yield losses from PVY are exacerbated because the disease also reduces the percentage of No. 1 and higher value spuds. Based on leaf testing of his research plots, Nolte learned that aphids, which are vectors of PVY, seldom spread the disease very far from infected plants. Nolte believes the observation affirms planting clean seed is the best way to control PVY.
The new farm bill retains PVY research funding, and McIntosh hopes to gather future data specific to the seed industry and necrotic PVY strains.
Nolte acknowledges the data makes several assumptions and must be taken with “a grain of salt,” but believes it evidences PVY is a “hidden drag” on production and affirms the importance of Idaho’s policy of laboratory testing every seed lot for PVY.
Based on his findings, McIntosh advises growers, “You need to be sure to not only look at current-season test results on seed lots but also ask for winter test results and make sure there wasn’t a differential between summer and winter tests.”
The numbers seem inflated to Oakley, Idaho, grower Randy Hardy.
“There’s a lot of things that affect yield, and to pin PVY down for that much sounds like a lot,” Hardy said.
But Hardy, who thus far hasn’t sought PVY test data from his seed supplier, acknowledges the damage highlighted in the report underscores PVY is “probably something we need to be watching a little more closely.”