Efeitos de herbicidas no desenvolvimento inicial da cana-de-açúcar e lixiviação, absorção e translocação de diurom

Abstract

Herbicides are the most widely used pesticides in the sugarcane sector, so it is interesting to note the level of tolerance and differences in sensitivity of new cultivars of sugarcane before the commercial release. The aims of this study were to evaluate the effects of inhibiting herbicides enzyme ALS (acetolactate synthase) and PSII (photosystem II) in different doses on eight different cultivars of sugarcane (commercial and future releases), study the absorption and translocation of 14C-diuron in three cultivars in pre and post-emergence of cane and to assess the leaching of this molecule in clay soil. The first experiment was conducted at the Center for Agricultural Sciences (CCA/UFSCar) with commercial cultivars RB835054, RB855156, RB867515, RB966928, and future releases RB975157, RB975201, RB975952 and RB985476, with a completely randomized design in a factorial arrangement 8x4 (8 cultivars x 4 doses) and three replications in a greenhouse. The vessels were filled with clay soil and were made pre-emergence applications of herbicides diclosulan, diuron, imazapic, imazapyr, metsulfuro-methyl and the mixture of products diuron, hexazinone and sulfometuronmethyl at doses of 0; 0.5; 1 and 2 times the commercial dose. Evaluations of phytotoxicity and height were performed at 7, 15, 30, 45, 60 and 90 days after emergence (DAE), and leaf area and shoot dry biomass at 90 DAE. The results showed that the cultivar RB975157 was more sensitive, RB867515 and RB966928 were intermediate and the most tolerant were RB975952 and RB985476; and having less effect with the metsulfuron-methyl and the greater effect with the imazapic and imazapyr. The others experiments were conducted in Ecotoxicology Laboratory of the Center for Nuclear Energy in Agriculture (CENA/USP), using the RB975157 (sensitive), RB985476 (tolerant) and RB867515 (intermediate) cultivars, using clay soil and the design was completely randomized and three repetitions. For the pre-emergence test, the surface layer of the soil received 14C-diuron, the absorption and translocation were evaluated by autoradiography, and the amount of herbicide in the wash water, soil and plant (shoots, roots and stalks). The evaluation times were 5, 10, 15, 20 and 25 DAE. The results showed that the absorption and translocation among cultivars was very low and the product was retained on the soil, however the more sensitive cultivar showed, comparatively, higher amounts of herbicide translocates the stalks. In postemergence, 14C-diuron was applied in the third fully expanded leaves of plants, and the assessments were made at 1, 2, 4, 8, 24 and 48 hours after application (HAA). It was found that most of diuron was not absorbed by the treated leaves over 48h and translocation was minimal for all three cultivars. The third experiment consisted in examining the leaching of 14C-diuron in 0-30.0 cm column glass filled with soil, and simulation 200 mm of rain, using CaCl2 solution. Assessments of leachate samples were taken at 12, 24, 36 and 48 HAA. The complete 48h, divided into 5.0 cm column of sessions in which the presence of the herbicide was measured in each session. The results showed that the leaching of diuron had low clay soil being retained in this layer of 0-0.05 m. Thus, it appears that there are differences in the sensitivity of sugarcane cultivars to herbicides; absorption and translocation in pre-emergence may vary between cultivars, but are similar in post; and diuron herbicide is a highly retained in clay soil. These information are very important to choose the most appropriate management and weed control in areas of cane sugar cultivation in order to provide better conditions for culture and minimize environmental impacts.