Control of Orobanche cernua in imidazolinone-tolerant sunflower hybrids

Abstract

Sunflower breeding for tolerance to imidazolinone-based herbicides began in 1997, and many sunflower seed companies and institutes are actively developing so-called Clearfield* sunflower hybrids tolerant to imidazolinone-based herbicides. Clearfield* production system for sunflower holds a lot of promise, including possibility of selective Orobanche cernua control. Field trials were conducted during 2001-2003 in northern Serbia to determine efficacy of imidazolinone-based herbicides on Orobanche cernua in Clearfield* sunflower hybrids. Used in the study were experimental hybrids from Nidera, Mycogen and commercial hybrid Rimi 2 from Institute of Field and Vegetable Crops. The following herbicides were studied: imazamox (20-48 g a.i. ha-1) and imazamox + imazapyr (33-39.6 + 15-18 g a.i. ha-1). Field studies focused on effects of herbicides and application timing (from one to eight pairs of sunflower leaves) on crop tolerance and O. cernua control. The efficacy of the herbicides in O. cernua control reached 100% at the time of sunflower flowering. At harvesting, the efficacy either remained the same or dropped a few percent depending on herbicide rates and time of application. Application of herbicides at the later stage of sunflower growth proved more effective. The yields obtained in the untreated check were significantly lower than those obtained in the treatments with herbicides. The phytotoxicity of the herbicides was transient and acceptable. Our results are indicative of the significant advancement and possibility O. cernua i control by growing imidazolinone-tolerant sunflower hybrids and application of imazamox and imazamox + imazapyr.