Effects of planting pattern and inter-row cultivation on competition between corn (Zea mays) and late emerging weeds

In addition to abiotic factors, weed-crop competition is one of the most frequent interactions between plants in the agroecosystem, where the outcome of the relationship depends on the ecological and genetic potential of the species, its development stage and population size, duration of interaction and environmental conditions in which the interaction occurs. Assessment of the critical time of weed control (CTWC) can be of great help in designing and applying the concept of integrated weed management. This study aimed to examine the influence of weed abundance in the treatment with and without pre-em application of herbicides [S-melolahlor (1.44 kg A.I. ha-1)+ terbuthylazine (0.75 kg A.I. ha-1)] in the beginning of CTWC in corn production in the area of southern Banat (Vojvodina province) in three meteorologically different seasons (2015-2017). The study was set up following randomized block design in three replications, with following treatments: T1season-long weedy plots, T7season-long weed-free; and five treatments with weeds growing until a specified corn development stage: T2three leaves (BBCH 13), T3six leaves (BBCH 16), T4nine leaves (BBCH 19), T5fifteen leaves (BBCH 34), and T6beginning of corn flowering (BBCH 52). The regression parameters and the CTWC parameters (DAE - days after emergence, BBCH - stages of corn development, GDD - Growing degree days) were calculated for a corn yield loss of 5%. During the three-year period, a positive correlation was confirmed between the reduction in the number and dry biomass of weeds m-2 against the time of weed removal and the achieved corn yields, i.e. the negative correlation between weed reduction and decline in corn yield. In meteorologically more favorable conditions (2016 with 526.4 mm of precipitation and 2017 with 336.0 mm of precipitation), with a pre-em herbicide application, the CTWC occurred later (58 and 36 DAE, respectively, BBCH 20 and BBCH 16 of corn). On the other hand, without a pre-em treatment, the CTWC occurred 6 to 3 weeks earlier (BBCH 11). In a drier season (2015, with 281.1 mm of precipitation) with pre-em herbicide application, the CTWC occurred 26 DAE (BBCH 14), while without herbicide application, it occurred 21 DAE (BBCH 12).