Field research was conducted in Arkansas for 3 yr to evaluate imazamox for control of diclofop-resistant Italian ryegrass in imidazolinone-tolerant wheat. Italian ryegrass was controlled at least 89% 49 d after wheat emergence (DAE) in year 2 and 3 by imazamox at 36 g ai/ha applied to one- to two-leaf wheat (POST1), by imazamox at 54 g ai/ha applied sequentially at POST1 followed by (fb) application to three- to four-leaf wheat (POST2), by pendimethalin at 1120 g ai/ha preemergence (PRE) fb imazamox at 36 or 54 g/ha POST1, and by chlorsulfuron plus metsulfuron at 22 plus 4 g ai/ha PRE. Italian ryegrass was controlled at least 95% 150 DAE with all applications in year 1 because of extremely cold temperatures and snowfall in December and January. Only sequential imazamox applications or pendimethalin PRE fb imazamox POST1 equaled the commercial standard, chlorsulfuron plus metsulfuron, for control of Italian ryegrass 150 DAE in years 2 and 3. These treatments controlled Italian ryegrass greater than 80% 150 DAE. Sequential postemergence applications of imazamox or programs containing pendimethalin PRE fb imazamox POST1 are necessary to optimize Italian ryegrass control and wheat yield in an imidazolinone-tolerant wheat production system.
Nomenclature: Chlorsulfuron; diclofop; imazamox; metsulfuron; pendimethalin; Italian ryegrass, Lolium multiflorum Lam. #3 LOLMU; winter wheat, Triticum aestivum L. # TRAES; ‘AP110CL’, ‘Washington’.
Additional index words: Diclofop resistance, sequential applications, wheat yield.
Abbreviations: AHAS, acetohydroxyacid synthase (EC 4.1.3.18); DAE, days after wheat emergence; fb, followed by; POST1, one- to two-leaf wheat; POST2, three- to four-leaf wheat; PRE, preemergence.
