Field vigor of sunflower seeds after chemical treatment

Abstract

Sunflower is a globally important oilseed, food and ornamental crop. To prevent the attack of insects and diseases during field emergence, sunflower seeds are usually treated with insecticides and fungicides, respectively. The ways in which they can influence seed germination and vigor are scarcely- known, especially if their effects are transferred to field emergence stage. Also, in sunflower there is no consensus as to which is the best estimator of sunflower seedling field emergence. In order to find out the best estimator, the present study was designed to i) determine the effects of insecticide treatment on sunflower seeds germination and vigor and, ii) estimate sunflower seedling field emergence by a correct association with the laboratory vigor test. Sunflower seeds were treated with tiamethoxam insecticide in commercial doses (6 ml kg-1 seeds) and compared with untreated seeds. Laboratory variables evaluated were: radicle emergence (G50), germination percentage (GP) and vigor by Electrical Conductivity (EC). Field vigor was evaluated by applying diverse formulas including chronological days (d) and thermal time (°Cd), using air (°Cd-Air) and soil temperature (°Cd-Soil). GP and G50 were not affected by the insecticide, but vigor was reduced. Only high correlations were detected between laboratory vigor (EC) and the field emergence speed when it was expressed in Mean time of emergence (TME) °Cd-Air, TME (°Cd-Soil) and Days for 50% of maximum emergence (SE50,°Cd-Soil) with coefficients of 0.77, 0.80 and 0.78, respectively. The insecticide did not exert negative effects on sunflower seeds germination. The lower vigor found in the laboratory conditions have been transferred to field conditions, causing a lower speed of seedlings emergence. The association with laboratory vigor test improves when the seedling field emergence variables (TME and SE50), include soil temperature in the thermal time calculation.