Mapeamento, habilidade competitiva, custo adaptativo e controle de biótipos de Amaranthus spp. resistentes a herbicidas

Abstract

Throughout the last years, technician and producers records have been pointing out deficiency in the weed control from the Amaranthus genus in the Rio Grande do Sul soy crops. The Amaranthus plants from this genus, also known as redroot pigweed plants, are considered difficult to control because they produce a great amount of seeds, have a long period of germination, emergency intermittent flow. It has been aimed through this paper to essay the redroot pigweed plants biotypes susceptibility in the Southern soy crops to the glyphosate, chlorimuron, glufosinate, fomesafen and 2,4-D herbicides; response - dose curve with A. retroflexus biotypes to the glyphosate and imazethapyr herbicides; identify and compare the adaptive value between susceptible and resistant biotypes of A. retroflexus; essay the competitive ability between resistant biotype of A. retroflexus and the soy culture; and search for alternative herbicides to the biotype control of the Amaranthus genus. The results showed that the redroot pigweed plants biotypes survived the glyphosate, imazethapyr or fomesafen applications. It is possible to ensure two redroot pigweed plants biotypes resistance (BR6 and BR3), originally from the city of Dom Pedrito (RS), with resistance factor greater than 10 to both biotypes and herbicides, calculated with the DM value. The susceptible biotype (BS3) showed better development during the firsts development stages, whilst the resistant biotype (BR6) was superior in most of the last evaluation variables, at 105 DAA. Soy outstanded competitively to the resistant A. retroflexus biotype (BR6) and it was concluded that the intraspecific interaction to soy and redroot pigweed plants was more harmful than the interspecific competition. The herbicides atrazine, saflufenacil, mesotrione, 2,4-D and dicamba were efficient in the initial control of Amaranthus spp biotypes. The usage of atrazine, 2,4-D and dicamba was efficient to control redroot pigweed plants over 7,5 cm tall. In pre emergency, the s-metolachlor, pendimethalin, atrazine, trifluralina, metribuzin e sulfentrazone herbicides were efficient in the redroot pigweed plants biotype control.