Weed management in soybean using burndown herbicides associated to pre-emergent herbicides

Abstract

The soybean crop has been playing a very important role in the agribusiness worldwide, including in Brazil. Among the pests that cause major problems to the crop are the weeds, because they are responsible by the reduction of the productivity and of the grain quality. On the face of it, this work aimed to evaluate the application of burndown herbicides associated to pre-emerging herbicides to the management of the soybean weeds. The experiment was carried out in the field, in area with no soil cover with fallow during the winter, in the randomized block design, with four replicates. The treatments used were: diuron + sulfentrazone (490 + 245), [glyphosate + (diuron + sulfentrazone)-1,440 + (420 + 210)], [glyphosate + (diuron + sulfentrazone)-1,440 + (490 + 245)], glyphosate + 2,4-D (1,440 + 806), glyphosate + diclosulam (1,440 + 25.2), [glyphosate + (imazethapyr + flumioxazin)-1,440 + (100 + 50)], glyphosate + saflufenacil (1,440 + 35), [ammonium-glufosinate + (diuron + sulfentrazone)-400 + 490 + 245 g ha-1 de i.a], and two herbicide-free controls, weedy and weed-free. At the 7, 14, 21 and 28 days after the emergency of the crop (DAE) the variables were evaluated, herbicide phytotoxicity on soybean and the weeds control, Digitaria ciliaris and Urochloa plantaginea. In the soybean harvest, the number of pods per plant was determined, the number of grains per pods, the mass of a thousand grains (g) and the grain productivity (kg ha-1). The phytotoxicity caused by herbicides to the soybean it was not over to 8% in all the evaluations realized. The control of the weeds, D. ciliaris and U. plantaginea were over to 90%, highlighting the effect of the pre-emerging herbicides in the maintaining of the control until the evaluation of the 28 DAE. In general, all the treatments involving the herbicides did not cause changes in the components of soybean crop yield, being statistically equal the weed-free control higher than the weedy control. The soybean presented an increase of 859.48% in grain yield when Digitaria ciliaris and of the Urochloa plantaginea was controlled. Highlighted Conclusions 1. The control of Digitaria ciliaris and Urochloa plantaginea is more efficient with the use of pre-emerging herbicides, mainly diuron + sulfentrazone and imazethapyr + flumioxazin. 2. The toxicity of herbicides to the soybean 'NA 5909' is low, with no visual intoxication symptoms from 28 days after emergency, and do not reduce the crop grain yield. 3. Digitaria ciliaris and Urochloa plantaginea can reduce by up to 88% the soybean grain yield if not controlled. 4. The soybean grain productivity can be increased by 859% when Digitaria ciliaris and Urochloa plantaginea are controlled.