Abstract Background Weed interference in the early stages of soybean development can compromise its yield. The use of herbicides with residual effects at the time of sowing is an alternative to reduce weed density and emergence time, consequently, the damage caused by their interference. Therefore, weed development can be reduced, which can result in easier post-emergence control. The combination of herbicide modes of action extends the spectrum of control and delays herbicide resistance evolution. Objective This work aimed to determine the onset of the critical period of weed control (CPWC) from the application of residual herbicides mixtures at soybean sowing. Methods Two experiments were carried out in 2021/2022, the first in a conventional tillage system with increasing periods of soybean/weeds coexistence (14, 28, 42, and 56 days after crop emergence). The second experiment consisted of a no-tillage system with soybean/weeds coexistence for 30, 45, 60, 75, and 90 days after crop emergence. On the day of soybean sowing, mixtures of the herbicides diclosulam + pyroxasulfone, flumioxazin + pyroxasulfone and diuron + sulfentrazone were applied, in addition to the untreated check. Soybean yield was evaluated evaluated upon harvest and data compared by non-linear regressions to CPWC determination. Results The application of residual herbicides can allowing reduces losses relative to the untreated control by up to 57%. CPWC beginning can be extended from eight to forty days, depending on mixes and acceptable losses. Conclusions The use of the mixture of residual herbicides are a good option for weed interference reduction for soybean crop.

Abstract The new technology of sugarcane planting, known as one-eye-set seedlings, offer a high standard of plant health and vegetative vigor. However, there are no reports in the literature that evaluate the weed competition with one-eye-set sugarcane seedlings, and the periods in which weed communities need to be controlled in this system. Two interference experiments were conducted in field conditions. The first experiment determined the periods of weed interference of an infesting community predominated by Ipomoea hederifolia and Merremia aegyptia in sugarcane. In the second experiment, these same species competed with plants of the same sugarcane cultivar. Productivity and qualitative aspects of production were evaluated. The critical period of interference prevention in one-eye-set sugarcane system was 103 days, with weed community interference starting at 35 days and lasting until 138 days after planting. Weed coexistence during the entire sugarcane cycle reduced productivity by 60% and affected qualitative characteristics such as the total reducing sugars. Both species affected the vegetative development of the crop, mainly the tillering. I. hederifolia plants developed ahead of the M. aegyptia plants but in late evaluations the interference caused by M. aegyptia (77%) was greater (P<0.01) than that caused by I. hederifolia (72%).