CONTROL OF DICOTYLEDONOUS WEED OCCURRENCE IN SPRING BARLEY

Our trials showed that spring barley could suppress dicotyledons effec tively even in the field with a higher weed seed bank in the soil; in a lot of cases, an application of herbicides was not effective because no significant influence on the yield was found. Spring barley can su ppress weeds and keep the field free of weeds till the harvest under c ertain conditions. The crop density plays an important role. It can be reached by an increased seeding rate or higher tillering. Conditions for powerful tillering based on cold weather and rainfall can be hardl y foreseen. In the past, tillering was also supported by nitrogen top dressing applied at the 3rd-leaf growth stage of barley. Now, this app lication is strongly limited or completely eliminated. With regard to the fact that possibilities for the optimum density at low seeding rat es are not sure it is necessary to reach the density required using a well considered seedling rate in relation to a variety. At adequate cr op densities (750 to 850 ears.m-2), weeds are supposed to wither away in the shade and other ones will not emerge. The trials also show that it is not always easy to select out a suitable herbicide or a combina tion of them to control weeds in spring barley. Even in trials where a number of weeds at the beginning of the growing season was quite high and exceeded threshold values, only a low or no yield increase was ob served after herbicide application. That can be caused either by the p hytotoxicity of herbicides or the fact that the weed spectrum did not reduce the yield in those stands. Spring barley sensitivity to herbici des differs from that of winter wheat and some products can be detrime ntal. Mostly, herbicide rates applied to spring barley can be much low er than those applied to winter wheat. To recommend the weed control i t is necessary to take into account that thresholds for weeds in sprin g barley are higher as compared to those in winter wheat. Weeds in win ter wheat grow faster (during autumn and winter) than the crop while i n spring, dicotyledons in spring barley grow slowlier than the crop in the field well prepared, and a strong competition of spring barley do es not allow emerged weeds to develop. For good competitive ability th e soil has to be well prepared in both the autumn and spring seasons. Not only the soil surface of the field should be treated because the c ompacted soil delays the initial crop growth and development. A suffic ient amount of air in the soil is very important for a weak root syste m of spring barley and together with early sowing will secure rapid ge rmination and growth. Agronomic and cropping practices for spring barl ey play a considerable role in consequent decision of using herbicides and their rates applied against dicotyledons in spring barley.