DOSE-RESPONSE MODELS FOR FLAME WEEDING IN RELATION TO PLANT SIZE AND DENSITY

Three models were evaluated to describe the dose-response relationship of flame weeding bioassays, with Sinapis alba L. in three field experiments on crop-free soil. In general, a logistic model gives a good description of plant number or fresh weight on the logarithm of gas dose of liquefied petroleum gas (LPG) in kg ha(-1). Plant size at treatment time had a major influence on the dose required, whereas plant density had a minor influence on the dose required to achieve a certain control level. To achieve a 95% control of plant number, LPG (propane) doses above 40 kg ha(-1) (1840 MJ ha(-1)) were needed far smaller plants with 0 to 2 true leaves, whereas plants with 2 to 4 leaves needed about 70 kg ha(-1). Considerably higher doses were required in 1992 because of drier weather than in 1990 and 1991. Doses about 40% lower were required to achieve a 95% reduction of fresh weight than those needed to obtain a similar reduction in plant number.