Seletividade de herbicidas sobre arroz irrigado em resposta à época de semeadura e redução da luminosidade em fases do desenvolvimento

Different environmental factors can have effect on the selectivity of herbicides on crops. The aim of this experiment was to evaluate the effect of sowing time and of artificial reduction of the luminosity at different stages of plant development on the herbicide selectivity and yield components of irrigated rice. The field experiment was carried out in 2012/2013 harvest, with the IRGA 424 cultivar. The factors studied were: sowing time (October 18 and November 9), herbicides (weeded control, bispyribac-sodium and penoxsulam) and stages of development of culture with luminosity reduced by 70% [control, seedling (S0-V4), vegetative and reproductive periods and entire cycle]. The experimental design was the completely randomized, in a factorial scheme, with four replications, but sowing time and reduced luminosity were imposed in strips, to make possible the experiment. Evaluated: visual phytotoxicity, stems and panicles per area, spikelets per panicle, spikelet sterility, thousand seed weight and yield. Data were subjected to analysis of variance by F test (p ≤ 0.05) and mean test of DMS Fischer (p ≤ 0.05). The sowing time influences the selectivity of bispyribac-sodium, and when held near the beginning of the period recommended, in October 18, reduces the yield of the cultivar studied. The artificial reduction of light in different phases of the development does not affect the selectivity of herbicides bispyribac-sodium and penoxsulam on irrigated rice.