VOLUNTEER POTATO CONTROL IN ONION USING FLUROXYPYR

Clark Oman, Scott J. Nissen, Phil Westra¹, Corey Ransom², Rick A. Boydston³, Martin M. Williams II⁴, W. Mack Thompson<sup>5

1</sup>Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523. ²Oregon State University, Ontario, OR 97914. ³USDA-ARS, Prosser, WA 99350. ⁴USDA-ARS, Urbana, IL 61801. ⁵Univeristy of Idaho, Parma, ID 83660 current address Pioneer Hybrids, Johnston, IA, 50131. Corresponding Author: Scott J. Nissen. Email: snissen@lamar.colostate.edu

Volunteer potatoes are difficult to control in onions with tillage or current post-emergent herbicide programs. Even small volunteer potatoes can emerge from significant soil depths and produce plants that reduce onion yields and serve as hosts for several important potato pathogens. Field research was conducted to evaluate crop safety and volunteer potato control using fluroxypyr in onion. Initial field studies evaluated potato (Russet Norkotah) response to fluroxypyr applications of 71 to 284 g ai/ha. All rates significantly reduced top growth and daughter tuber yields. Potato variety response was evaluated by applying fluroxypyr at rates of 142, 213, and 284 g ai/ha to four potato varieties representing several market classes: chipping (Chipeta), red fresh-market (Sangre), and white fresh-market (Russet Norkotah and Russet Nugget). Norkotah was the most sensitive variety, while Nugget and Chipeta response was intermediate. Sangre was the most tolerant variety, producing a significant number of daughter tubers at the highest fluroxypyr rate. Onion response to fluroxypyr applied alone and in sequential applications with oxyfluorfen plus bromoxynil was evaluated under weed-free conditions. Onion yields were similar to the control for all treatments, including a 560 g ai/ha fluroxypyr application to four leaf onions. Volunteer potato biomass and daughter tuber yield were significantly reduced by the same treatments including three applications of oxyfluorfen plus bromoxynil. Fluroxypyr provided better control of potato top growth than three applications of oxyfluorfen plus bromoxynil; however, reductions in daughter tubers were similar. Fluroxypyr effectively controlled volunteer potatoes and onions appear to have acceptable tolerance.

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