Fitossociologia de plantas daninhas em cultivos de feijão sobre diferentes manejos de herbicidas

Knowledge on changes in weeds communities caused by weeds management practices is important when effective strategies for the control of these species are set. A field experiment was conducted to assess the effects of herbicides applications with different sprayer boom heights on the weeds dynamics and beans yield. A 3x4+1 factorial arrangement was adopted, comprised of the combination of three herbicides (fomesafen. fluazifop-p-butyl and a mixture of both) and four different boom heights (0.20; 0.30; 0.40 and 0.50 m above target) and one control (non-weeded check). Thirty days after application (DAA), the following phytosociological indices were determined: relative frequency, relative density, relative dominance, and importance value. Sixty days DAA, yield rates were determined. Prior to the experiment installation, 22 species were identified in the entire experimental area. The species Alternanthera tenella , C helidonium majus , D igitaria horizontalis and Bidens pilosa dominated the area where there was no weed control. Reduced boom heights for application of fomesafen diminished the importance of dicot species. In the plots with fomesafen + fluazifop-p-butyl applications, the number of dicot weeds was greater than the other species, with predominance of A. tenella e B. pilosa . In general, the similarity index between the different herbicides and different boom heights was low, which indicates that the treatments used result in different weeds populations. Bean crops reduces the weeds diversity, and the application of herbicides has a positive effect on weeds infestation, with consequent gains in productivity.