Response of Canola Brassica napus and Associated Weeds to Newly Introduced Herbicides in Iraq

Abstract

Field experiement was carried out during winter season of 2001/2002 and 2002/2003 at the Field Crops Station (formerly IPA Agricultural Research) to investigate Brassica napus L. and associated weeds to newly introduced herbicides and determine their selectivity in canola for approval and registration in Iraq. The experiement included the following treatments:- Preemergence application of clomazone (48% q.i) at 0.24 and 0.3 lit. product/ha, preplant– application of napropamide (50% q.i) at 2 and 2.8 lit. product/ha, postemergence application of pyridate (45% q.i) at 2 kg product/ha, preplant application of trifluralin (44.5% q.i) at 2.4 lit. product/ha. Hand – weeded and weedy – check treatments were also included for comparison Randomized Complete Block Design was followed to arrange the treatments. Results revealed the efficacy of clomazone, napropamide and pyridate in controlling broadleaf and reducing weed densities to an averages of 6 – 12.6 plants/m2 compared to 58 plant/m2 at the weedy plots. Grass densities were decreased to 0 – 12 plants/m2 compared to 12 plants/m2 for the untreated weedy check. Pyridate showed no activity on grasses. The reduction in weed densities resulted in low weeds dry weight: 9 - 38 gm/m2 for the herbicide – treated plots compared to 193 gm / m2 of the weedy – check. Clomazone caused significant injury on canola foliage which was reflected by discoloration (bleaching) and plant stunting. Plant height was reduced by both rates of clomazone to 49 – 52 cm compared to 98 cm for the hand – weeded plots. Variable effects of herbicides were observed on canola yield components and this was reflected on final seed yield wheras clomazone caused noticeable reduction in seed yield: 634 – 940 kg/ha, although with its high efficacy on weeds. Napropamide increased seeds yield to 1304 kg/ha at 2.8 liters/ha application rate and was as close as to that of the hand – weeded plot seeds yield. Long – season weeds competition with canola caused high percent of reduction; 60 %, the yield was reduced from 1368 kg/ha of the hand – weeded plots to 540 kg/ha of the weedy – plots. In 2002 - 2003, the same trend of effects of herbicidal weed control treatments on weeds was found and clomazone caused 40 – 50 % injury on canola foliage. From these results, clomazone can not be recommend and approved to use in canola due to its noticeable injury on canola while napropamide can be applied preplant in this crop at 2.8 liters/ha to control broadleaf and grassy weeds and pyridate at 2 kg/ha can be used postemergence for broadleaf weeds control under irrigated regions of Iraq.