Common Cocklebur (Xanthium strumarium L.) is an emerging aggressive & invasive weed in crop fields in the Khyber Pakhtunkhwa (KP) Province of Pakistan. Among the crops, maize has been severely affected by X. strumarium in the region. In order to evaluate the competitive ability of X. strumarium in maize, field experiments were conducted at Agricultural Research Farm, KP Agricultural University Peshawar, Pakistan during 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 per square meter, whereas seven contrasting densities of X. strumarium viz., 0, 2, 4, 6, 8, 10 and 12 plants per square meter were allotted to the subplots. During both the years, the grain yield of maize was highest in control plots (maize monoculture) at density of 7.5 plants per sq m. The density of X. strumarium at 8-12 plants per sq m reduced maize yield by 40 and 43% in 2006 and 2007, respectively indicating that X. strumarium is a strong competitor in maize. However, in both the experiments, the maize yield losses were rather comparable (24-26%) at all crop densities.

Maize is the third main cereal crop after wheat and rice in Pakistan, and second after wheat in Khyber Pukhtunkhwa. Horse purslane (Trianthema portulacastrum L) a member of family Aizoaceae, is a common weed of maize, cotton and vegetables all over Pakistan (Hashim and Marwat, 2002). Due to indeterminate habit, vegetative and reproductive growth continues for the entire life span (Nayyar et al., 2001). Out of 69 weed species T. portulacastrum was realized as the most aggressive weed of maize crop (Kumar and Singh, 1983). At a density of 12 plants m-2 of T. portulacastrum gave lower maize yield of 3.54 t ha-1 than weed-free plots 3.89 t ha-1 (Ansar et al., 1996), and infestation can lead to 32.3% losses in maize crop (Balyan and Bhan, 1989). Horse purlane caused 25 million dollars loss to maize production each year in Pakistan (PhD Thesis of Muhammad Saeed).