Ecological Studies on the Interference of Xanthium Strumarium L. With Maize Zea Mays L. at Different Densities

Common Cocklebur (Xanthium strumarium L.) is one of the emerging aggressive and invasive weeds of waste lands and crop fields in the North-West Frontier Province of Pakistan. Although of subtropical origin, it has also invaded regions of colder climates. Among the crops, maize has been perceived to be more severely affected by X. strumarium in the region. Therefore, in order to evaluate the competitive ability of X. strumarium in maize, field experiments were conducted at Agricultural Research Farm, NWFP Agricultural University Peshawar, Pakistan for two crop seasons (Summer/Kharif 2006 and 2007) using a Randomized Complete Block Design with split plot arrangement replicated three times. The main plots comprised of four varying maize densities: 5, 7.5, 10, and 12.5 plants m -2 , whereas seven contrasting densities of X. strumarium viz., 0, 2, 4, 6, 8, 10 and 12 plants m -2 were allotted to the subplots. The crop parameters (percent emergence m -2 , days to tasseling, silking, and maturity, plant height, leaf area, leaf area index, number of grains cob -1 , thousand grain weight, biological yield, grain yield and harvest index) and the weed parameters (plant height, leaf area, leaf area index, fresh biomass) were all significantly different between the two years due to the substantial disparity in the environmental conditions. The aggressiveness of X. strumarium was higher in 2006 as compared to that in 2007 obviously as a consequence of prominent inequality in the rainfall (184 vs. 48 mm) and average temperature (28 vs. 32 °C), which differently affected the yield and yield-related traits in maize. Therefore, the crop parameters were better in 2006 than in 2007 which implied that the mutual effect of the crop and weed on each other was somewhat consistent. During both the years, the grain yield of maize was highest in control plots (maize monoculture) at density of 7.5 plants m -2 . The density of X. strumarium at 8-12 plants m -2 reduced the maize yield by 40 and 43% in 2006 iiand 2007, respectively. However, in both the experiments, the maize yield losses were rather comparable (24-26%) at all crop densities. The tasseling and silking stages of maize, and ultimately the crop maturity were delayed by a gradual increase in the weed density. The highest biological yield of maize was noticed in the highest crop density (12.5 plants m -2 ) which progressively diminished with reduction in the crop density. Consequently, a higher biomass of X. strumarium was noted in the lowest maize density. Therefore, majority of the crop and weed parameters were significantly affected by an increase in the density of either species. Moreover, higher values were recorded for leaf area and leaf area index of either species during 2006 as compared to 2007. The biomass of X. strumarium increased with increasing density and also dependent on maize density; the higher the maize density the lower was the weed biomass. However, a considerable vegetative growth of X. strumarium was recorded even at the highest maize density indicating that the crop density alone can not curb X. strumarium below the threshold level. In view of the two years study, it can be deduced that X. strumarium is a strong competitor in maize crop that can result in remarkable yield losses in maize depending on the crop and weed density. The data suggest that the crop density alone is not sufficient enough to cope effectively with the X. strumarium competition; therefore, multiple cultural approaches should be employed to predict the crop yield losses due to competition with the weed. Key words: Maize, corn, cocklebur, density, Zea mays, Xanthium strumarium, crop- weed competition, interference.