Published online: Feb 09, 2012 Herbicide, Seed Potatoes
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ABERDEEN, Idaho-Symptoms of glyphosate contamination in seed potatoes vary by variety, and tubers sustain severe damage without exhibiting foliar symptoms when exposure occurs after bulking starts, new research suggests.

Weed scientist Pamela Hutchinson, with the University of Idaho Aberdeen Research and Extension Center, added daughter crop yields may be dramatically reduced even when affected seed shows none of the telltale visible signs, such as rough skin and folding.

Based on her results, Hutchinson believes growers face greater challenges than they previously realized in identifying when seed has been marred by glyphosate drift or residue in spray tanks.

In 2008, Hutchinson teamed with weed scientists from Oregon State University and the USDA Agricultural Research Service in Washington to study the effects of glyphosate-the active ingredient in Monsanto's widely used herbicide Roundup-on Ranger Russet seed.

Glyphosate doses ranged from 3 percent of the standard rate, simulating drift, to as high as 25 percent of the standard rate. Glyphosate was applied when plants were 4 to 6 inches tall, at tuber initiation and at midbulking. The Ranger seed from the 2008 trial was planted the following year.

In 2011, Hutchinson collaborated with UI Extension seed potato specialist Phil Nolte to repeat the experiment with Russet Burbank, adding an extra application to simulate killing vines with an uncleaned tank previously used for glyphosate.

"This whole glyphosate drift issue is an emerging problem, I would say," Nolte said.

In Rangers, the greatest yield losses within the mother crop occurred when glyphosate was applied at hooking and tuber initiation. The Burbank mother crop was hardest hit when plants were 4 to 6 inches tall but showed little impact at hooking.

Though glyphosate introduced at midbulking didn't damage the mother crop in either variety, emergence was dismal, averaging less than 20 percent, when the Ranger daughter crop was planted. Hutchinson expects similar results for Burbank.

A prior small-scale test by Nolte shows Burbank daughter seed exposed to glyphosate can sprout underground in a candelabra pattern. That defect hasn't surfaced in Ranger daughter tubers.

The Idaho Crop Improvement Program agreed to plant Hutchinson's 2011 Burbank daughter seed at no charge in its annual winter grow-out.

"If we can catch this problem at winter grow-out, we can help seed potato growers not sell that seed from that particular lot," she said.

Hutchinson also reserved some of the seed to plant this spring. She hopes to conduct future glyphosate drift research with Shepody and a red variety, using lower herbicide concentrations and residue testing in tubers.

Gary Smith, a field inspector with the Crop Improvement Program, said a couple of seed growers have made special requests that their samples be inspected for herbicide damage in this winter's grow-out. Typically, Smith said herbicide damage is detected in one or two lots per year.

"Growers need to be aware of what is being sprayed around their seed potato fields and make sure any spray equipment used on their potatoes is thoroughly cleaned or not used on any other crop," Hutchinson said.

SOURCE: John O'Connell, Capitol Press