Be a Good Neighbor

Glyphosate carryover in seed

Published in the February 2013 Issue Published online: Feb 28, 2013 Phillip Nolte, UI seed potato pathologist, Pamela
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"Figure 1. Russet Burbank daughter tubers from mother sprayed with glyphosate. Folds and cracking appeared on the bud end of some of the tubers, but not all. Rough, elephant-hiding also was present on some tubers. The trial was conducted at the UI Aberdeen R&E Center. Courtesy photo.
"Figure 2. Multiple sprouting, sometimes called "candelabra sprouting," can occur in daughter tubers from mother plants that have come into contact with glyphosate spray/drift. This multiple sprouting also can be caused by other factors such as seed aging. Courtesy photo.
"Figure 3. Aberdeen R&E Center 2012 research trial: five days after the Shepody mother crop had 1/16X glyphosate rate applied at mid-bulking. Courtesy photo.

Once again, University of Idaho Potato Cropping Systems Weed Scientist Dr. Pamela J.S. Hutchinson, and Extension Potato Seed Specialist Dr. Phil Nolte want to remind all who use glyphosate in seed potato-production areas that glyphosate on the mother seed crop can carryover in the daughter tubers to affect sprouting and plant health the following season. These daughter tuber plants can have multiple sprouting, poor emergence, stunting and yellowing similar to symptoms caused by a direct glyphosate spray or drift. Research has shown that not all potato varieties react the same to glyphosate. A seed grower may not even know that the mother crop has encountered glyphosate because the symptoms may be fleeting or non-existent.


How does this happen?

 Drift from applications to adjacent fields

1) Early- to late-season applications in Roundup Ready crops, e.g. sugarbeet, corn, alfalfa, soybean.

2) Late-season weed control in wheat or barley after hard dough stage and 30 percent or less grain moisture.

3) Perennial weed control in non-crop land or fallow fields in seed-growing areas.

 Spot-spraying around seed potato field margins and/or within the potato crop.

 Poor sprayer tank, boom, injection/mixing system clean-out after glyphosate use and before use on the seed potato crop.


Do's and Don'ts with glyphosate in seed potato areas:

 Do not spot-spray in seed potato fields or on field margins.

 Avoid spraying glyphosate within 100 yards of a seed potato field, especially after tuber bulking begins. When possible, avoid glyphosate applications in fields adjacent to seed potatoes.

 If possible, do have a sprayer-boom system dedicated to use in potatoes, only which will never be used for glyphosate and non-potato herbicides.

 Follow good application practices-pay attention to the surrounding conditions. For instance, be aware of wind speed and direction and stop spraying when speed at spray boom height is more than 4 mph, even though labels may state higher wind speed cut-offs.

 Do not let a sprayer-boom system stand overnight with glyphosate in that system or without cleaning thoroughly after glyphosate is used that day.

 Do clean out the tank, boom and entire spray system after using glyphosate and before moving on to a different application.

1) There are many reputable spray-tank cleaner products available.

2) Triple-rinse the whole system, and don't forget the end of the boom past the nozzles and the mixing equipment!

3) Let the spray tank cleaner remain in tank and boom overnight.

 Ask the custom applicator/neighbor about the previous uses of his/her sprayer about to be used in or around seed potatoes. Although they more than likely have cleaned out the spray system properly, they may not know about the risks of glyphosate to seed potatoes.

 If you suspect that your mother crop has encountered glyphosate somehow, foliar and tuber samples can be collected and analyzed for glyphosate residues.



Throughout the year, seed potato growers, custom applicators and anyone using glyphosate in a seed potato production area should be talking with each other!

 If you are an applicator, know where the current-year seed potato fields in the area are located.

 If you are a seed potato grower, understand which areas near your seed fields may be receiving glyphosate sometime during the growing season.