Italian ryegrass has become one of the most common and troublesome weeds of wheat production in the Southern United States. There are multiple reports in this region of Italian ryegrass herbicide resistance to acetyl-CoA carboxylase (ACCase), acetolactate synthase (ALS), and glyphosate herbicides. One commonality for Italian ryegrass resistance in this area is that most of these mechanisms of action for these herbicides are all postemergence (POST) applied. In order to have profitable soft red winter wheat production, applications of preemergence (PRE) herbicides with residual control of Italian ryegrass and other winter weed species would benefit growers. There are a very limited number of herbicides that can be applied at the time of wheat planting, primarily only when pyroxasulfone is registered for this timing. Research was conducted to establish weed control information when herbicides were applied to soft red winter wheat PRE, at wheat emergence (AE), or POST at Feekes stages 1.0–1.9, depending on herbicide label recommendations. Injury from any pyroxasulfone PRE treatments up to 120 g a.i. ha−1 was transient and did not affect wheat yield for any experiment. Italian ryegrass control was variable depending on location and year. Susceptible and diclofop-resistant Italian ryegrass control was 86% or greater with pyroxasulfone at 60 g a.i. ha−1 and greater with applied PRE. Italian ryegrass control was variable ranging from 27 to 49% with pendimethalin ME-applied PRE, diclofop at Feekes sage 1.0, and pinoxaden applied at Feekes stage 1.9.
Part of the book: Wheat Improvement, Management and Utilization