Tolerância diferencial a herbicidas e habilidade competitiva de espécies de capim-colchão

Abstract

In the Digitaria genus, some of the main weeds of the sugarcane agroecosystem are found. The direct interaction with the culture negatively affects the development and productivity. The control of these species are constantly done with the application of herbicides, which has proportioned a selection of biotypes of the Digitaria nuda specie tolerant to photosystem II inhibitors and Acetolactate synthase inhibitors. The flora genus identification, located in areas treated with herbicides where there were control failures, was done to verify the possible existence of D. nuda tolerant biotypes. Agronomic efficacy tests were also done to the pre-emerging herbicides and dose curve response, the photosystem II inhibiting herbicides in biotypes D. nuda in conventional and organic areas. The results revealed that the escapes are not exclusively derived from the selection of the D. nuda species and that there is variability in the degree of tolerance between biotypes, which are correlated with the application of diuron herbicide. The occurrence of escaping species, considered susceptible to the herbicides, indicates a possible existence of competitive ability differentiated among the species. To verify the existence of differentiated competitive ability, an experiment in replacement series between D. nuda (Dn), D. ciliaris (Dc), D. horizontalis (Dh), and D. bicornis(Db) species was done, following comparisons: there were Dn X Dc, Dn Db X, Dn X Dh, Dh Db X, X Dh Dc and Db X Dc. In most of the comparisons, an equivalent competition occurred between the species, however the Db specie demonstrated to be more competitive than Dc specie. For Dn and Dh, the intraspecific competition was more important than the competition with plants from other species. On condition where there is water availability in 100% of the field capacity, Dn specie presents the highest potential of development. Concerning the absence or presence of nutritional deficiency, the plants had development similar area part. In conditions where there is no nutritional deficiency, the Dh species showed a higher capacity to develop their roots. Keywords: Crabgrass. Digitaria spp. Pre-Emergence Herbicides. Taxonomic identification of crabgrass. Competitive ability.