ORIGINAL PAPER Influence of nitrogen and plant density on the growth and seed production of common ragweed (Ambrosia artemisiifolia L.) Robert Leskovsek • Avishek Datta • Andrej Simoncic • Stevan Z. Knezevic Received: 22 December 2011 / Accepted: 16 April 2012 / Published online: 5 May 2012 Ó Springer-Verlag 2012 Abstract Common ragweed is an important annual weed in crop production, and is also considered to be a serious public health problem. Determination of common ragweed growth under various nitrogen (N) rate and plant density could aid the development of an integrated control pro- gram. Greenhouse and field experiments were conducted to determine the effects of N fertilizer and density on com- mon ragweed growth and seed production. In the green- house study, the greatest shoot dry matter (SDM) plant -1 was obtained with the 50 and 100 kg N ha -1 . In the field experiment, SDM plant -1 in the low density plots responded favorably to the addition of medium and high levels of N compared to the field level of N. With increasing density, ragweed in higher density plots responded only with the highest N rate. The intensity of intraspecific competition increased with increasing density, thus total SDM plant -1 was significantly reduced, regard- less of N rate. Intraspecific competition also reduced the reproductive production of common ragweed where seed production decreased as plant density increased. Plants grown at higher density produced less seeds per plant basis; however, they produced a considerable number of seed on a per area land basis, which is important for the survival of the species and further expansion in agricultural land and non-crop areas. Common ragweed is a fast-growing spe- cies, capable of producing considerable biomass and seed at various pure stand densities and N rates. It also justifies the need for early season control to prevent seed production. Keywords Intraspecific competition  Fertilizer Growth analysis  Invasive  Weed biology Introduction Common ragweed (Ambrosia artemisiifolia L.) (hereafter referred to as ragweed) is a native to the prairie region of North America. It was introduced to Europe in the mid eighteenth century, and since then it has spread over many European countries (Chauvel et al. 2006; Vogl et al. 2008). Ragweed is of particular concern because of allergic reactions to its pollen, which causes ocular and respiratory allergies that often develop into asthma (Taramarcaz et al. 2005; Gauvrit and Chauvel 2010). In North America, ragweed pollen is the most commonly known as an important cause of hay fever (allergic rhinitis) (Mitich 1996) and a form of dermatitis in some people (Fisher 1996). Ragweed is also considered a troublesome summer annual weed in field crops because of its early emergence, and ability to compete for light, water, and nutrients (Rauch et al. 2007; Patracchini et al. 2011). In North America and in Europe, ragweed emergence typically peaks in April and May when soil temperatures increase to approximately 14 °C (Myers et al. 2004; Kazinczi et al. 2008). Mature plants range in height from 0.3 to 2.0 m, which can obstruct harvest procedures (Rauch et al. 2007). Ragweed has been reported to be one of the most Communicated by M. Traugott. R. Leskovsek  A. Simoncic Agricultural Institute of Slovenia, Hacquetova ulica 17, 1000 Ljubljana, Slovenia A. Datta  S. Z. Knezevic (&) Department of Agronomy and Horticulture, Haskell Agricultural Laboratory, Northeast Research and Extension Center, University of Nebraska, Concord, NE 68728-2828, USA e-mail: sknezevic2@unl.edu 123 J Pest Sci (2012) 85:527–539 DOI 10.1007/s10340-012-0433-2