Identificação de espécies, suscetibilidade a herbicidas e habilidade competitiva de milhã (Digitaria spp.) no Estado do Rio Grande do Sul

Abstract

Crabgrass is within the group of the most damaging weed species in the agricultural area of RS, occuring on rainfed and irrigated crops, causing harm to these cultures. The objectives of this study were to identify the species of Digitaria occurring in agricultural areas of RS, to evaluate their susceptibility to herbicides, to compare the relative competitive ability between large crabgrass and soybeans and rice, to determine the competition periods of large crabgrass in these cultures. The species D. ciliaris occurs throughout the RS, predominantly in areas of the soybean crop in the northern half of the state, where D. bicornis also occurs. In the region of rice, the southern half of RS, and D. ciliaris, there is D. sanguinalis, while the species D. aequiglumis, D. eriostachya and D. ternata are found less frequently. Digitaria species are susceptible to clethodim, glyphosate and there are hebicide-tolerant populations to cyhalofop. The competitive ability of Digitaria is smaller than the cultivated species of rice and soybeans, when it occurs in the same proportion of plants. Still, the rice can live with the large crabgrass for a maximum period of 18 days after emergence without reduction in productivity; while soybean should remain free from large crabgrass for a period between 23 and 50 days after crop emergence.