Efeito de fatores ambientais e tolerância a herbicidas em três espécies de plantas daninhas da família Rubiaceae

The strong selection pressure exerted by intensive use of glyphosate in cultivated areas has selected populations of the Rubiaceae weed species Borreria latifolia (Aubl.) K.Shum. (broadleaf buttonweed), Galianthe chodatiana (Standl.) E.L. Cabral (galiante) and Richardia brasiliensis Gomes (Brazilian pusley) with differential sensitivity to this herbicide in the South region of Brazil. The control of these weeds with herbicides is troublesome and signals the need to incorporate management practices of ruderal flora and crops, more sustainable and that results in more efficient control for long-term. Therefore, it is very important to expand the information about their biology and management. This study aimed: (a) select efficient methods to overcome dormancy of B. latifolia and G. chodatiana and determine how they influence the kinetics of seeds germination; (b) analyze the effects of temperature, irradiance, pH, aluminum and salinity on seed germination and initial growth of the B. latifolia, G. chodatiana e R. brasiliensis seedlings; (c) evaluate tolerance to glyphosate levels in biotypes of B. latifolia, G. chodatiana e R. brasiliensis through dose-response curves and compare two methods to evaluate herbicidal control; (d) and evaluated the effectiveness of alternative herbicides in pre-emergence and in early and late post-emergence of the three species. The treatment with KNO3 2%/3h + gibberellic acid 400 ppm resulted in higher percentage of G. chodatiana seed germination. This treatment and also the dry heat (60°C/30 min) + KNO3 2%/3h were more effective in overcoming dormancy of B. latifolia. G. chodatiana and R. brasiliensis tolerate lower temperatures during the germination process, while B. latifolia tolerate higher temperatures. B. latifolia and R. brasiliensis are positive photoblastic while G. chodatiana is indifferent to the photoperiod. B. latifolia shows higher germination and early development in pH 3, while G. chodatiana and R. brasiliensis prefer pH range between 5 and 7. B. latifolia and G. chodatiana were more tolerant to the aluminum during the germination process than R. brasiliensis. Low salt levels were sufficient to reduce the seed germination of the three species. Some biotypes of B. latifolia and R. brasiliensis showed medium-high glyphosate tolerance, not being controlled by higher doses than recommended. The G. chodatiana specie was not controlled with the highest dose used, showing a high glyphosate tolerance. The sulfentrazone, s-metolachlor and saflufenacil herbicides sprayed in pre-emergence showed high efficacy both on B. latifolia and R. brasiliensis, while chlorimuron-ethyl and diclosulan were effective only on R. brasiliensis. In early post-emergence the fomesafen, lactofem and flumioxazin herbicides efficiently controlled plants of all species, while bentazon showed high efficacy only on B. latifolia. Noteworthy the susceptibility of the G. chodatiana specie for applications in early post-emergence, because the control effectiveness and the number of effective herbicides are reduced with increasing the plant age. Many treatments with tank mix or sequencial applications with glyphosate, were effective in controlling B. latifolia and R. brasiliensis plants in advanced stage of development.

Habilidade competitiva do feijoeiro e sua tolerância ao herbicida Ethoxysulfuron

The presence of weeds decreases the crop yield. Among the alternatives to reduce the crop yield loss, it can be included to increase the competitive ability of the crop and the chemical control of the weeds. A research program was developed in the course of Agronomy at Federal Technological University at Paraná, Campus Pato Branco - PR, during the years 2015/16, with the objectives evaluating if gibberellin inhibitors increase the competitive ability of bean plants, making them insensitive to the initialism, extending the period prior to weed-crop interference. Evaluate the tolerance of common bean plants to the herbicide ethoxysulfuron and investigate the existence of relationship between the plant mass and the level of tolerance of the plants to the herbicide. Evaluate the effect of increasing doses of ethoxysulfuron on morphological characteristics, yield components and grain yield of the bean cultivars IPR Tangará and IPR Andorinha. Evaluate the effect of increasing doses of ethoxysulfuron on the development of IAC Imperador and the community of weeds present in the area. Elucidate the mechanism that confers tolerance to bean plants to the herbicide ethoxysulfuron. The results indicate that gibberellin inhibitors were not effective in increasing periods of weed-crop coexistence. Trinexapac-ethyl increased 20% the grain yield of bean plants. It was observed high variability as the response of bean cultivars to the herbicide ethoxysulfuron, however, despite high doses (200 g ha-1), it was not observed death of the plants. The field results indicate that when the ethoxysulfuron dose is 83.2 g ha-1, the reduction in grain yield can reach 40% with the cultivar IPR Tangará and 30% in the cultivar IPR Andorinha. However, respectively for each cultivar cited, ethoxysulfuron at 17 and 12 g ha-1 are enough to reduce 10% of grain yield. Evaluating the control of weeds within the bean crop cultivar IAC Imperador with the herbicide ethoxysulfuron, it was observed that doses at 20 g ha-1 are enough to control soybean and Ipomoea spp. plants. But, due to the level of plant injury, the crop grain yield increase was not sufficient to match the one observed on the weed-free untreated control. The mechanism of tolerance of bean plants to ethoxysulfuron appears to be the herbicide degradation.