Timing of Weed Control in No‐Tillage Wheat Crops

Timing of successful weed control in no‐tillage wheat is not well known, yet weeds, especially annual grasses, may reduce yields considerably in such crops. To evaluate the effect of weed control on no‐tillage wheat production, a 2‐yr study of the timing of wheat/weed interference was initiated in southeastern Australia, a region that effectively has a winter‐wet/summer‐dry climate. In this study, weeds were controlled either manually or chemically at various stages of crop growth. Wheat yield or dry weights were determined at harvest. Additionally, soil temperature, soil water, and available soil N were monitored throughout the growing seasons. If autumnal rains commenced early and the crop was sown early (i.e., before May), then significant wheat/weed competition took place only in May. However, if the crop was sown late (i.e., after May), then wheat/weed competition occurred only in early September. In all cases, wheat/weed competition increased when soil temperature exceeded 10°C and resulted in rapid depletions of available soil N.