PRODUTIVIDADE DA SOJA E DO TRIGO EM FUNÇÃO DE MANEJOS DE PLANTAS DANINHAS EM PÓS-EMERGÊNCIA E DA DESSECAÇÃO EM PRÉ-COLHEITA

Abstract

The inclusion of RR soybean resistant to glyphosate caused changes in weed control, since glyphosate has been used more frequently, resulting in the occurrence of resistant weeds. Therefore, management techniques that reduce the number of glyphosate applications in the production system and the possibility of using alternative herbicides are necessary. Accordingly, three independent experiments were conducted on the Farm School of the State University of Ponta Grossa, Ponta Grossa, PR. The first experiment ( E1 ) aimed to evaluate the selectivity of glyphosate used on its own or in combination with bentazon, clethodim, chlorimuron ethyl, fenoxaprope-p-ethyl, fenoxaprope-p-ethyl + clethodim, fomesafen, glufosinate ammonium salt, imazethapyr and sethoxydim at commercial doses in soybean cultivars of Coodetec 202RR, 206RR, 248 and 250, Brasmax Potência and Apolo and Nidera 5909, 7321 and 6411. In the experiment 2 (E2), the objective was to assess the desiccation effects of wheat pre-harvest and the effects of this desiccation in the culture as well as in the occurrence of weeds in soybean sown in succession. In this experiment the wheat cultivar used was Quartzo, desiccated in the pre-harvest with diquate at doses of 300, 400 and 500 g.ha-1 and glufosinate ammonium salt at doses of 300 and 400 g.ha-1. In experiment 3 ( E3 ) the soybean, Energia cultivar RR, was sown after the wheat harvest and in the same place in order to assess if the desiccation of wheat affects the occurrence of weeds in soybean cultivar Energia BMX RR sown in succession and also if the desiccation of this soybean with diquate at a dose of 400 g.ha-1 interferes with soybean yield. In E1, among the graminicides at 7 DAA (days after application) the highest values of phytotoxicity were observed by the use of the clethodim and fenoxaprop-p-ethyl herbicides, and in subsequent assessments no differences of phytotoxicity were observed among the graminicides, which in combination with glyphosate resulted in slight increase of phytotoxicity. Among the latifolicide mixtures, glufosinate ammonium salt was the one which caused the highest phytotoxicity and the combination of these latifolicide with glyphosate resulted in lower phytotoxicity. The phytotoxicity caused by herbicides did not affect soybean productivity, but the combination of them with glyphosate promoted its improvement due to the control of weeds promoted by glyphosate. In E2 , the herbicides diquate and glufosinate ammonium salt promoted desiccation higher than 97 % of leaves and 82 % of the stalks of wheat in five days after its application, diquate having a faster action compared to glufosinate. These herbicides applied in wheat pre-harvest desiccation reduced grain moisture, promoted higher hectoliter weight and did not affect the wheat yield. In E3, the diquate and glufosinate ammonium salt applied in the desiccation of pre-harvest wheat reduced weed populations in soybean sown in succession, especially up to 14 days after soybean sowing and the desiccation of pre-harvest soybean did not affect the culture yield.