Weedy sunflower (Helianthus annuus L.): the first report in Argentina

CANTAMUTTO, MIGUEL; PRESOTTO, ALEJANDRO; CASQUERO, MAURICIO

Congreso; Biolief 2011. 2nd World Conference on Biological Invasions and Ecosystem Functioning; 2011

Sunflower, Helianthus annuus L., one of the major oilseed crops in Argentina share area with the invasive H. annuus biotype naturalized in the last 60 years. Weedy H. annuus can cause economic losses and is of concern because of the potential gene flow with herbicide-tolerant sunflower crop. In Tres Arroyos district (Buenos Aires), which had no record of invasive populations, a sunflower field with 5 ha invaded (n¡Ü11 plants m-2) by weedy H. annuus was identified in 2009. Two years later the sunflower crop area invaded by weedy plants in the field reached 20 ha. Measurements were made over 30 random plots (1 m2). Weedy plants showed intermediate morphology between wild and domesticated sunflower, height ¡Ü 3.5 m, several heads (n>17), stem anthocyanins and reproductive structures. Principal component analysis showed that yield decreased when weedy plants density (d) increase (r=-0.48**). Two-way ANOVA showed yield losses while invasive plants density increased, exceeding 50% (**) for weed densities >3 plants m-2. Rectangular hyperbolic model fitted with 2009 and 2011 data with percentages of yield loss per unit (d¡ú0) between 38.7 and 62.4, and percentages of yield loss (d¡ú¡Þ) between 65.6 and 73.1. These results confirm that weedy H. annuus can appear in non-colonized habitats possibly linked to human activities like hired agricultural machinery. Due to the high interference capacity is essential to make an integrated management of this biotype to prevent the dispersion in the country.