Data from surveys are used to help quantitatively diagnose the relative importance of chemical and nonchemical management practices, identify weed problems, and provide potential solutions. However, to our knowledge, such surveys have not been conducted in Argentina. In 2016, advisors and crop producers from cropping areas across Argentina were surveyed through email with the objectives to identify the main weed species problems and assess the use of chemical and nonchemical weed management practices in different crop production areas in Argentina. Fleabane, pigweed, johnsongrass, fingergrass, goosegrass, barnyardgrass, and ryegrass were considered the most important weeds. More than 53% of the producers used only chemical options; 86% used chemical fallow (i.e., keeping weed free with chemical application); 62% used full herbicide rates; 46% used proper herbicide timing; 41% used multiple modes of action; and 32% used rotation of herbicide modes of action. The main nonchemical practices used were crop rotation (45%); avoiding seed production during (31%) and after (25%) the crop cycle; narrow row spacing (19%); and cultivars with greater competitive ability (18%). Less than 15% of the people surveyed used increased crop densities or altered date of sowing. There is a high dependence on chemical control in the main crops grown in Argentina. Extension efforts are needed to emphasize the importance of integrated weed management.

Summary Digitaria sanguinalis is a troublesome annual weed that causes important yield losses in different crops. Despite this, there is scarce information about different aspects of its biology under field conditions. New knowledge about the establishment process of this species will be of paramount importance in order to maximise the effectiveness of weed management. The aims of this paper were to evaluate the effect of stubble found on the surface on seed dormancy levels through the season, the effects of stubble and soyabean crop canopy on seedling emergence and to determine the field emergence pattern as a consequence of seed dormancy level at dispersal time. Seeds on the soil surface, which showed a high dormancy level at the beginning of autumn, were released from dormancy by low winter temperatures and germinated during spring as temperatures rose, showing a transient surface seedbank. Seeds covered by stubbles had delayed the emergence in the field due to lower alternating temperatures perceived by the surface seedbank. On the other hand, the presence of a soyabean crop and stubble together reduced the number of seedlings. Seeds with a high dormancy level at dispersal time showed a delayed emergence in the next season when compared with seeds with a lower dormancy level. However, the final number of seedlings was similar. Both stubble on surface and crop canopy are useful factors to lessen and delay the seedling emergence allowing the design of weed management strategies in order to diminish the population levels of this species.

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The adoption of dicamba-tolerant crops has reduced the challenge of controlling glyphosate-resistant Amaranthus palmeri in these crops. However, introducing herbicide programmes with new mechanisms of action and different intensities can favour major shifts in weed communities. This can affect not only the functionality of the agroecosystem, but also resource availability to the most problematic species. The objectives of this work were to evaluate how herbicide programme structure and intensity affect (a) weed diversity, (b) population growth rate (λ) of weed species and (c) weed community structure based on λ dynamics in a dicamba-tolerant cotton monoculture. To achieve these objectives, a cotton field experiment was established to compare four herbicide programmes from 2011 to 2018. The herbicide programmes differed in the first 4 years (i.e. glyphosate every year, alternating glyphosate and glyphosate plus dicamba every other year, glyphosate plus dicamba every year, and residual herbicide and glyphosate plus dicamba every year). During the last 4 years, all programmes received glyphosate plus dicamba. The weed seedbank was evaluated every spring and λ calculated. Environmental variation from year to year was more important in determining weed richness than herbicide programmes, which exhibited similar richness across all treatments during the eight years of the study. Regardless of herbicide programme, most species maintained λ between zero and one. Only a few species were the exception with λ values above one, such as A. palmeri, Mollugo verticillata and Eleusine indica. Although glyphosate plus dicamba reduced λ for several species, this herbicide mix was less effective in reducing λ for other weeds compared with glyphosate alone, suggesting a potential antagonism that could change weed community composition. The limited changes in λ for most species suggest the capacity of weeds to adjust reproduction and survival to overcome changes in mortality rates caused by increases in herbicide use intensity.