Abstract
Field experiments were carried out over three years (2004-05, to 2006-07) to study the efficacy of a post-emergence dual-purpose herbicide (mesosulfuron - methyl (3%) + iodosulfuron - methyl - sodium (0.6%) + mefenpyr - diethyl (9%) to control Lolium rigidum Gaud. and broad-leaved weeds in no-till wheat (Triticum aestivum L.). A ready herbicide mixture was used at three doses (6+1.2, 9+1.8 and 12+2.4 g a.i./ha) on two dates (beginning of tillering for L. rigidum and 2-3 pair of leaves for broad-leaved weeds, and complete tillering for L. rigidum and 5-6 pair of leaves for broad-leaved weeds) with three different application volumes (100, 200 and 300 L/ha). The results of the present study reveal that using lower than the recommended dose (12+2.4 g/ha), the herbicide mixture controls L. rigidum better than it controls some broad-leaved weeds. Effective weed control, which was achieved mainly through the application at the first weed development stage, provided higher grain yields. The lower control efficacy of more developed L. rigidum and broad-leaved weeds and a longer period of competition between crop and weeds are responsible for the significantly lower crop yields for the delayed application. Within each application timing significant differences were obtained among the dose/volume combinations, with the exception of the first application regarding L. rigidum control, indicating that a reduction in herbicide dose is possible, but only for certain dose/volume combinations. Nonetheless, weed control was maintained across an array of dose/volume combinations, especially with L. rigidum, thus, our results demonstrate that reduced doses can effectively control weeds if applied early.
Highlights
Wheat (Triticum aestivum L.) is the most important winter cereal grown in Portugal and is severely limited by grass and broad-leaved weeds
Numerous reasons can account for this variation, but we suggest that application timing and application volume may be two factors affecting herbicide efficacy
The aim of the present paper is to explore the possibility of reducing the input of a post-emergence herbicide mixture to control L. rigidum and broad-leaved weeds in wheat under no-tillage, while maintaining acceptable weed population levels and satisfactory crop yields
Summary
Wheat (Triticum aestivum L.) is the most important winter cereal grown in Portugal and is severely limited by grass and broad-leaved weeds. Annual ryegrass (Lolium rigidum Gaud.) is one of the most troublesome weeds in cereals in Mediterranean climates (Recasens et al, 1997; González-Andújar and Saavedra, 2003). Yield losses in cereal crops due to competition from ryegrass can reach up to 80% depending on the infestation level (Izquierdo et al, 2003). Broad-leaved weeds are a problem in many wheat growing areas in Portugal. The most common method of controlling weeds is by using herbicides. Experimental results, obtained from numerous experiments in Spain, indicate that the level of ryegrass control achieved with commercial herbicides at recommended doses usually ranges from 57% to 99%, with an average value of 90% (Fernández-Quintanilla et al, 1998; Navarrete et al, 2000)
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