A field trial on chemical control of rat’s tail fescue (Festuca myuros) in rapeseed fields was carried out in the period 2012-2014. The following herbicides registered for application in rapeseed, were used in the experiment: Butisan 400 SC (metazachlor – 400 g/l), Butisan Max (metazachlor – 200 g/l + dimethenamid-P – 200 g/l + quinmerac – 100 g/l), Stratus ultra (100 g/l cycloxydim + tensid), Agil (100 g/l propaquizafop + surfactant), Fusilade forte (150 g/l fluazifop-P-butyl) and Cleranda (17,5 g/l imazamox + 375 g/l metazachlor). It was established that very good results were achieved in the control of rat’s tail fescue after timely treatment with the herbicide chemical Butisan 400 SC. Another reliable alternative for control of that weed species was the application of the herbicide Cleranda at the rate of 150-200 ml/dka, when using Clearfield technology. The results of the trial showed that three of the registered herbicides against grassy weeds in rapeseed – Stratus ultra, Fusilade Forte and Agil, did not display any herbicide efficacy against rat’s tail fescue, regardless of treatment rate and time of application. The only vegetation herbicide showing very good results is Cleranda. The results of the present study show that treatment applied at the stage of 4th–6th leaf has a slightly better effect compared to the variants with earlier (2nd–4th leaf) and later (6th–8th leaf) treatments. The earlier treatment is more risky for secondary weed infestation, the level of which can be lower or higher in the different years. The delayed treatment, especially if carried out in spring, reduces the herbicide effect of the active substance imazamox against grassy weeds, including rat’s tail fescue.
Chemical control of rat`s tail fescue (Festuca Myuros) in rapeseed fields