Habilidade competitiva e nível de dano econômico de papuã (Urochloa plantaginea) em milho

Abstract

Corn is of great importance in the Brazilian economic scenario, and the alexandergrass (Urochloa plantaginea) is one of the weeds that cause the greatest damage to this crop, which, when uncontrolled, can reduce grain yields of up to 90%. The objective of this work was to evaluate the relative competitive ability, the interference and the economic damage level of corn hybrids infested by the alexandergrass. In the first study, experiments were carried out to evaluate the competitive ability of corn hybrids in the presence of alexandergrass plant populations, both conducted in substitution series, with different species combinations. The analysis of the competitiveness of the species was carried out through diagrams applied to substitutive experiments and also by the relative competitiveness indexes. At 50 days after the emergence of the species, the leaf area (LA) and the dry mass of the aerial part (DM) of the plants were checked. There was competition between the corn hybrids and the alexandergrass, being both species negatively affected, independently of the proportion of plants, provoking reductions in the LA and in the DM of the species. In the second study the interference and the economic damage level of alexandergrass populations in competition with corn densities (2,60; 3,10; 3,65; 4,00 and 4,80 plants m-1) were determined in competition with ten alexandergrass populations for each crop seeding density. The variables population of plants, leaf area, soil cover and dry mass of alexandergrass aerial part were evaluated as indicator of infestation. The nonlinear regression model of the rectangular hyperbola adequately estimates the yield losses of corn grains in the presence of alexandergrass populations. Corn densities of 2,60; 3,10 and 3,65 plants m-1 in the average of all evaluated variables were more competitive than the others in the presence of alexandergrass. Seed densities 2,60; 3,10 and 3,65 plants m-1 increase the economic damage level, justifying the adoption of control measures of the alexandergrass in the higher populations. The increase in grain yield, corn price, herbicide efficiency and reduction in the cost of control decrease the level of economic damage, justifying the adoption of control measures in low alexandergrass populations and that interspecific competition causes smaller losses to LA and DM of species than intraspecific competition. When comparing the species among themselves, corn was more competitive than the alexandergrass.