Estimation of critical period of exotic invasive weed Alternanthera philoxeroides interference in maize.
Alternanthera philoxeroides, a quickly spreading troublesome invasive weed of summer crops, is causing substantial yield losses in maize and other crops in Pakistan. Influence of A. philoxeroides at different weed free (full season, 3, 4, 5 and 6 weeks after crop emergence (WAE)) and weedy periods (full season, 3, 4, 5 and 6 WAE) on maize was estimated during two consecutive years (2013 and 2014). The increasing weed competition periods increased weed dry biomass (up to 646%) and nutrient uptake (876-1377%). Weed competition caused reduction in maize plant height (14%), 100-grain biomass (22%), number of grains (31%) and grain biomass per cob (30%). Different A. philoxeroides competition periods caused up to 37% and 45% biological and grain yield losses of maize, respectively. Relative weed competitive index range was 3.14-45.10%. Four parameter logistic model predicted 0.26-6.04 WAE and 0.35-5.86 WAE as critical period of competition for A. philoxeroides to avoid 5% to 10% maize grain yield losses, respectively. The comparatively narrow window for competition period might be due to its fast and prostrate growth habit, high nutrient uptake and strong allelopathic potential. Appropriate management strategies would help to condense anticipated spread of A. philoxeroides and maize yield losses.