Determinaten: das Ertragspotential der Kultur ohne Unkrautkonkurrenz, die Unkrautdichte und die Entwicklungsstadien von Unkraut und Kultur bei der Behandlung. Die Beweiskraft der benutzten Daten zeigt, daB eine fast lineare Beadehung zwischen der Unkrautdichte bei der Behandlung und dem Ertrag besteht. Das Modell basierte auf dieser Erwartung, die zur sehr kurvilinearen Beziehung zwischen Ertrag und unbehandelter Verunkrautung in Gegensatz steht. Dieser Unterschied wird darauf zuruckgefuhrt, daB behandelte Unkrauter eine geringere Konkurrenz ausliben als unbehandelte.

Biologically active residues of the herbicides metsulfuron-methyl, chlorsulfuron and triasulfuron were estimated with field pea bioassays in soil samples to 80 cm depth from 4 field trials in south-eastern Australia situated on neutral to highly alkaline soil. Residues were both mobile and persistent at low levels. Leaching occurred beyond the lowest sampling depth during the winter–spring growing season. Metsulfuron-methyl was the most mobile of the 3 herbicides. Plant-back experiments involving susceptible crop and pasture species on 2 of the sites showed that the rates of decline of these residues in the sampling zone were slower than might be inferred from label plant-back recommendations in 1 of 2 seasons.

In a series of 12 field experiments in 1990 and 1991, metsulfuron-methyl at rates of 2.1, 4.2, and8.4 g/ha (0.5, 1.0, 2.0 times the maximum recommended label rate of the commercial product) was applied at the early tillering stage to commercial barley crops in South Australia.At 4 sites, applications of 4.2 and 8.4 g/ha of metsulfuron-methyl resulted in a marked reduction in plant molybdenum concentrations for at least 6 weeks and grain yield reductions of about 10% resulted from applications of metsulfuron-methyl resulted in a temporary reduction in the concentrations of phosphorus and/or zinc for at least 4 weeks, followed by substantial recovery within 6 weeks. Temporary minor reductions in manganese, copper, sulfur, and potassium concentrations were also measured in the metsulfuron-methyl treatments at 3 sites. At harvest, no nutrient reduction due to chemical treatments was measured in grain samples from any site. Three weeks after the application of 4.2 and 8.4 g/ha of metsulfuron-methyl, marked decreases in total root length were measured in all diameter classes. We suggest these decreases are implicated in the plant these treatments. On these 4 sites and 5 others, nutrient reductions. Applications of metsulfuron-methyl at 4.2 and 8.4 g/ha resulted in grain protein increases of 0.3-0.4%, independent of yield.

Summary Using a previous model as a base, data derived in field trials in wheat (Triticum aestivuort L.) and bailey (Hordeum vulgare L.) were assessed to estimate the yield penalty, and resulting reduction in economic benefit, from progressive spraying of herbicides up to late crop tillering. Compared with early post‐emergence application, yield penalties from delayed spraying began at early tillering. For median values of weed‐free yield and weed density in the data set. the loss in potential yield increase when spraying at late tillering compared with early post‐emergence was 71%, Crops with higher weed‐free yield potential and with greater initial weed density showed a proportionately (as well as absolutely) larger yield penalty from a moderate delay in spraying, indicating an earlier and more intense onset of competition with weeds.

In 11 experiments over 6 seasons the herbicide sethoxydim was applied to Machete, Spear and Blade wheat cultivars in the absence or near absence of weeds (10 sites) or where the weeds were controlled by selective herbicides (1 site), in the cropping area north of Adelaide, South Australia. The rates applied included 9-47 g a.i./ha at the 2-3 leaf growth stage and 9-74 g a.i./ha at early tillering. Except for the very long growing season of 1992, there was a highly significant positive linear correlation between the number of degree days in the growing season at each experimental site and relative mean yield increase of these sethoxydim treatments. Yield increases ranged from nil in growing seasons of about 1000 degree days to 32% in a growing season of 1480 degree days, with a median of 8% over the experiments.