The Use of Norflurazon (Zorial 5G) in Parker Valley Alfalfa For Purple Nutsedge Suppression in 1997-98

Two experiments were conducted during 1997-98 to study the use of norflurazon (Zorial 5G) for purple nutsedge control in alfalfa. In experiment 1, Zorial 5G was applied in spring 1996 and 1997 at application rates of 1.0, 1.5, 2.0, and 3.0 lb a.i. /A. Split applications were made each summer in four of eight treatments for total annual Zorial 5G rates of 2.0, 3.0, and 4.0 lb a. i. /A-year. In the fall of 1997, each plot was divided into two subplots. One set of subplots was disced twice and replanted with alfalfa. Alfalfa planted into these subplots was not affected by the residual soil concentrations of norflurazon. In the other set of undisturbed subplots, the residual soil concentrations of norflurazon continued to provide substantial suppression of purple nutsedge in 1998. However, by August 1998, the 3 lb a.i. /A-year rate only provided fair nutsedge suppression (51 %), while the 4 lb a. i. /A-year rate still provided satisfactory suppression (75 %). At rates of 2 lb a.i. /A-year or less, the residual effects of norflurazon declined to low levels in 1998 and did not keep purple nutsedge population levels from rebounding t