Abstract:

Aims Goosegrass (Eleusine indica), one of the world’s malignant weeds, is also a widespread weed in the cotton (Gossypium hirsutum) fields along the Yangtze River in Anhui. Cotton is highly sensitive to weed competition. This research aims to determine the density competition effect of goosegrass on cotton and to identify its critical period for control, thereby allowing farmers to make well-formed decisions to further improve the management of goosegrass in cotton fields.

Methods From 2010 to 2012, two experiments were conducted at an experimental site in Anqing, Anhui. In the density competition experiment, an additive series was used. The cotton density was kept constant while eight densities of goosegrass (0, 0.125, 0.25, 0.5, 1, 2, 3, and 4 plants·m^-1) were tested. This aimed to determine the effects of varying goosegrass densities on cotton growth and yield. In the critical control period experiment, different durations of weed interference and weed-free periods (0, 2, 4, 6, 8, 10, 12, 14 and 20 weeks after crop emergence) were investigated to determine how goosegrass affects cotton.

Important findings As the density of goosegrass increased, its plant height gradually decreased. Compared to 0.125 plants·m^-1 goosegrass, the plant height of goosegrass at densities of 3 plants·m^-1(2011) and 0.25 plants·m^-1 (2012) was significantly decreased. On average over three years, goosegrass biomass per unit area increased from 715 kg·hm^-2 (0.125 plants·m^-1) to 4 148 kg·hm^-2 (4 plants·m^-1). This indicates that intraspecific competition among goosegrass becomes more pronounced at higher densities. In 2012, the number of tillers and biomass per plant of goosegrass gradually increased with increasing weedy duration, and the height of goosegrass exceeded that of cotton during the first 12 weeks after crop emergence. With the increasing weed densities, the plant height and stem diameter of cotton decreased, while the number of fruit branches and bolls per plant were significantly reduced. The single boll mass was also reduced at higher densities of goosegrass, however, weed density did not significantly change the lint percentage. In 2012, the plant height of cotton significantly decreased at densities of over 2 plants·m^-1. The cotton stem diameter was remarkably reduced at densities of 3 plants·m^-1 or more in 2011 and 4 plants·m^-1 in 2012, respectively. Goosegrass even at the density of 1 plants·m^-1 reduced the fruit branch numbers, the boll number per plant and single boll mass of cotton by 8.7% to 11.6%, 18.6% to 35.2% and 0.1% to 4.6%, respectively. The seed cotton yields were significantly reduced at densities of 0.125 plants·m^-1 (2010 and 2012) and 0.25 plants·m^-1 (2011), with reductions ranging from 10% to 18%. The boll number per plant of cotton and seed cotton yield loss rate followed a hyperbolic model in response to goosgrass density. It is predicted that goosegrass at a density between 2.3 to 3.7 plants·m^-1 would result in a 50% reduction in the number of bolls per plant, while densities of 0.05 to 0.09 plants·m^-1 would lead to a 5% reduction in seed cotton yield. The increased competition duration of goosegrass resulted in a gradual decline in the height and stem diameter of cotton plants. The increased competition duration also significantly reduced the number of fruit branches and bolls per plant. A Logistic relationship exists between the seed cotton yields and the competition duration of goosegrass. Conversely, with an increasing weed-free duration, cotton plants exhibited greater height and stem diameter, along with a notable rise in the number of fruit branches, bolls per plant, and seed cotton yield. The increase in seed cotton yield with prolonged weed-free duration followed a Gompertz model. The critical period for controlling goosegrass at a density of 2.5 plants·m^-1 was between 35 to 83 days after cotton planting, based on a 5% yield-loss threshold.

Key words: weed competition, goosegrass, cotton, threshold of weed competition, critical control periods for weed