03213naa a2200229 a 450000100080000000500110000800800410001902200140006002400590007410000200013324501800015326000090033352024100034265000230275265300660277570000170284170000150285870000170287370000200289070000220291077300510293221357042021-10-29       2021    bl uuuu     u00u1 u    #d  a2675-94627 ahttps://doi.org/10.51694/AdvWeedSci/2021;39:000012DOI1 aAGOSTINETTO, D.  aPeriod prior to interference of barnyardgrass is modified due to the spraying of cyhalofop-butyl alone or associated with penoxsulam in paddy rice crop.h[electronic resource]  c2021  aWeed occurrence is one of the main obstacles to the expression of the production potential of crops. Competition for one or more limiting environmental resources (CO2, water, light, and nutrients) can generate irreversible losses to crops, and there may be no recovery of their development even after the removal of the stress caused by weeds or inclusion of limiting resources to the environment (Karimmojeni et al., 2014). The average losses in rice yield due to the coexistence with weeds are estimated between 40 and 60%, reaching up to 96% in cases of lack of control (Chauhan and Johnson, 2011). The degree of weed interference is determined according to the species, density, location, availability of resources, and emergence period relative to the crop (Datta et al., 2017). However, the losses caused to the crop can be altered as the period in which the weed community coexists with the crop changes. Crop and weeds can live together at the beginning of development for a certain period without causing quantitative or qualitative losses to the crop (Silva et al., 2014). This stage, called the period prior to interference (PPI), corresponds to the period after emergence or sowing in which the crop can coexist with the weed community without negatively affecting yield or other characteristics (Silva et al., 2014). However, control measures must be adopted at the end of this period so that crop yield is not compromised (Silva and Durigan, 2006). Studies of competition periods conducted with the rice crop have shown that PPI duration can vary from 7 to 26 DAE (Silva and Durigan, 2006; Zhang et al., 2003). Variations in topography, climate, crop genetics, and management practices affect weed composition, weed density, and emergence time relative to the crop and, consequently, affect PPI (Korres and Norsworthy, 2015). This variability needs to be understood for the better use of the integrated weed management of each environment. Among the weed species in rice fields, barnyardgrass (Echinochloa spp.) stands out relative to the others due to its highly competitive ability compared to the crop (Agostinetto et al., 2008). The importance of this weed is due to its morphophysiological similarities with rice plants, denoting the potential for yield losses because of competition, as well as high infestation levels and a wide distribution in commercial crops (Andres et al., 2007).  aGenetic background  aWeed competition is one of the main constraints to rice yield1 aSOUZA, E. A.1 aANDRES, A.1 aULGUIM A. R.1 aSCHIMITZ, M. F.1 aGOULART, F. A. P.  tAdvances in Weed Science, V. 39, p. 1-6, 2021.