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1 October 2009 Resistance of a Prickly Lettuce (Lactuca serriola) Biotype to 2,4-D
Ian C. Burke, Joseph P. Yenish, Dennis Pittmann, Robert S. Gallagher
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Dose-response experiments were conducted on a biotype of prickly lettuce collected from Whitman County, WA, to determine the level of resistance to 2,4-D. Initially, progeny of prickly lettuce that survived two applications of glyphosate and 2,4-D in mixture were collected to determine if antagonism of the 2,4-D or glyphosate was occurring. Prickly lettuce survival was determined to not be due to antagonism of 2,4-D or glyphosate when the two herbicides were applied in mixture. The doses required to reduce growth 50% (GR50) for resistant and susceptible field-collected prickly lettuce were 150 and 6 g ae/ha 2,4-D, respectively, indicating the resistant biotype was 25 times more resistant to 2,4-D than the susceptible biotype. The resistant biotype expressed injury but produced regrowth following application. A dose of 2,4-D at 220 g/ha was required to reduce regrowth frequency 50% (FR50) for resistant field-collected prickly lettuce. Regrowth was also observed with the susceptible biotype, although the FR50 was much lower (10 g/ha), resulting in an R/S ratio of 22 based on the respective FR50 values. A rate of 4,300 g/ha 2,4-D (10 times the maximum labeled rate in wheat) was required to reduce the regrowth frequency in the resistant biotype to zero.

Nomenclature: 2,4-D; glyphosate; prickly lettuce, Lactuca serriola L. LACSE; wheat, Triticum aestivum L.

Ian C. Burke, Joseph P. Yenish, Dennis Pittmann, and Robert S. Gallagher "Resistance of a Prickly Lettuce (Lactuca serriola) Biotype to 2,4-D," Weed Technology 23(4), 586-591, (1 October 2009).
Received: 8 January 2009; Accepted: 1 July 2009; Published: 1 October 2009

Herbicide resistance
synthetic auxins
winter wheat
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