Effect of different doses of post-emergence-applied iodosulfuron on weed control and grain yield of malt barley (Hordeum distichum L.), under Mediterranean conditions

A study was carried out over a two year period (2009/2010 and 2012/2013) on an experimental farm in the Alentejo region (Beja), in southern Portugal where rainfed malt barley (Hordeum distichum L.) is sown at the end of autumn or beginning of winter (November– December). The aim of this experiment was to study the efficiency of the herbicide iodosulfuron-methyl-sodium to control post-emergence broadleaved weeds in this cereal crop. The malt barley crop was established using no-till farming. This technology provides the necessary machine bearing capacity of the soil to assure the post-emergence application of herbicides at two diferente weed development stages. The herbicide iodosulfuron-methyl-sodium was applied at three doses (5.0, 7.5, and 10.0 g a. i. · ha–1) and at two different broadleaved weed development stages (3 to 4 and 6 to 7 pairs of leaves), that also corresponded to two diferente crop development stages (beginning of tillering and complete tillering). The results indicated that early herbicide application timing provided a significantly higher efficiency for all the applied herbicide doses, but this better weed control was not reflected in a higher crop grain yield. The lack of a higher crop grain yield was probably due to a crop phytotoxicity of the herbicide, when used at an early application timing.

Controlo de infestantes monocotiledóneas com diferentes doses de herbicidas em pós-emergência de trigo mole (Triticum aestivum L.) de sementeira directa

Neste trabalho estudou-se a eficiência dos herbicidas Herbipec 500 FL (s.a. Clortolurão) e Dopler Super (s.a. Diclofope-Metilo+Fenoxaprope-P-Etilo+Mefenepir-Dietilo) no controlo, em pós-emergência de infestantes Monocotiledóneas, e na produção de grão e suas componentes, na cultura do trigo mole em sementeira directa, combinando doses inferiores às recomendadas pelos fabricantes. Os ensaios decorreram nos anos agrícolas de 2006/2007 e 2007/2008, na Herdade do Louseiro no concelho de Évora e na Herdade da Revilheira no concelho de Reguengos de Monsaraz, respectivamente. Na experimentação efectuou-se o estudo dos dois herbicidas, com 3 níveis cada, correspondentes a nove tratamentos. O delineamento experimental foi em blocos casualizados com quatro repetições cada. Verificou-se uma maior eficiência no controlo das plantas infestantes de Lolium rigidum Gaud. e de Juncus bufonius L. e, consequentemente, um maior número de grãos e uma produção de grão de trigo elevada com 2 litros ha-l de Herbipec 500 FL e 0,5 litro ha-1 de Dopler Super. ABSTRACT: The purpose of this work was to study the efficiency of the herbicides Herbipec 500 FL (a.i. chlorotoluron) and Dopler Super (a.i. diclofop-methyl + fenoxaprop-P-ethyl + mefenpyr-diethyl) to control grass weeds at post-emergence in no-till bread wheat and consequently to do the evaluation of potential grain yield combining reduced doses to the recommended ones by the manufacturers. The trials were carried out over two growing seasons (2006/2007 and 2007/2008) on the farm "Revilheira" and on a private farm "Louseiro", both in the district of Évora. Trials to study effects of three doses of a two herbicides, with three levels each, corresponding to nine treatments were executed. The experimental design was a randomized block with four replications each. The results showed a great efficiency and grain yield wheat with the mixture with 2 l ha-1 Herbipec 500 FL and 0,5 1 ha-1 Dopler Super to controlling Lolium spp. and Juncus bufonius L..