Sugarbeet tolerance and weed control efficacy with split applications of phenmedipham plus desmedipham

Sugarbeet and weeds were treated with phenmedipham plus desmedipham either as single applications or as split applications in which 50% of the equivalent single application rate was applied at each application. Split application did not alter the phytotoxicity to the crop when environmental conditions did not predispose the Sugarbeet to injury by the herbicide. Split applications at 1-1 or 1-4 kg ha^?1 spaced from 0-5 to c. 5 days apart caused more injury to the crop than the respective single applications when environmental conditions were such that injury to the crop resulted from the single applications. Injury to Sugarbeet following application of 0-72 kg ha^?1 of phenmedipham plus desmedipham was always low, regardless of the type of application. Susceptible weeds were controlled by single applications of 1 1-1 ?4 kg ha^?1, but 0-72 kg ha^?1 did not reliably provide adequate control. Split applications c. 3-8 days apart gave improved control. Control achieved by 0-72 kg ha^?1 of the herbicide applied as split treatments equalled or exceeded that produced by single applications of 1-4 kg ha^?1. Improvement in the control of tolerant weed species by split applications of phenmedipham plus desmedipham was species dependent. Use of low-rate split applications of phenmedipham plus desmedipham thus resulted in reduced injury to the Sugarbeet, and the introduction of less herbicide into the ecosystem, while maintaining or improving the control of susceptible weeds.