ARS | Publication request: Aminopyralid Residue Impacts on Potatoes and Weeds

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 2012
Publication Date: N/A

Interpretive Summary: Aminopyralid is used in Alaska and other regions in the Western U.S. to control certain invasive weed species. In Alaska aminopyralid appears to have an extended soil half-life due to cold temperatures resulting in carry-over injury in potatoes. Field studies at three experiment stations in Delta Junction, Fairbanks, and Palmer, Alaska were established to determine the response of weeds and potatoes to low doses of aminopyralid applied to the soil. Both prostrate knotweed and narrowleaf hawksbeard were susceptible to aminopyralid. Potatoes were highly susceptible to injury from aminopyralid at low doses. At Delta Junction and Fairbanks, visual injury of potatoes greater than 25% was observed at 15 g ae ha-1 aminopyralid, whereas at Palmer visual injury was greater than 40% at 8 g ae ha-1, the lowest rate tested. Potato tuber production was reduced by aminopyralid at rates of 15 g ae ha-1 and above at both Delta Junction and Palmer. Aminopyralid concentration in daughter tubers increased with increasing field application rates, with 30 ppb found in tubers grown at the highest application rate (123 g ae ha-1). Plants grown from daughter tubers were severly distorted and many daughter tubers failed to sprout or produce normal shoots. Aminopyralid use should be avoided in potato rotations in Alaska to prevent possible damage to potatoes.

Technical Abstract: Aminopyralid is used in Alaska to control certain invasive weed species; however it appears to have an extended soil half-life in interior Alaska resulting in carry-over injury in potatoes. Field studies at three experiment stations in Delta Junction, Fairbanks, and Palmer, Alaska were established to determine the dose-response of soil-applied aminopyralid (0, 8, 15, 31, 62, and 123 g ae ha-1) for control of weed populations and above and below ground potato growth. Both prostrate knotweed and narrowleaf hawksbeard were susceptible to aminopyralid. At Delta Junction and Fairbanks, visual injury of potatoes greater than 25% was observed at 15 g ae ha-1 aminopyralid, whereas at Palmer visual injury was greater than 40% at 8 g ae ha-1, the lowest rate tested. Potato tuber production was reduced by aminopyralid at rates of 15 g ae ha-1 and above at both Delta Junction and Palmer. Sub-samples of potato tubers from Delta Junction and Palmer were analyzed for aminopyralid content and grown out to determine if aminopyralid in tubers would reduce subsequent growth. The aminopyralid concentration in potato tubers increased with increasing field application rates, with 30 ppb extracted from tubers grown at the highest application rate (123 g ae ha-1). All plants grown from daughter tubers except from control plots in Palmer exhibited injury symptoms. The number of emerged shoots, and shoot height decreased with increasing aminopyralid concentrations in the tuber, with injury rates greater than 70% at 8 g ae ha-1.