Abstract
The influence of weed growth stage on the efficacy of selected herbicides applied at reduced doses was investigated under pot experiments at the Institute of Soil Science and Plant Cultivation - State Research Institute in Wrocław. Three weed species were used as tested plants: <i>Anthemis arvensis</i> L., <i>Chenopodium album</i> L. and <i>Stellaria media</i> L., which were sprayed at different growth stages: 2-4, 6-8, and 10-12 leaves. The experiment included the following herbicides: tribenuron-methyl, iodosulfuron methyl sodium + amidosulfuron, and metribuzin + amidosulfuron, used at full doses and reduced by 25 and 50%. Three weeks after treatment, fresh weight of weeds was determined. Weed control was significantly related to weed species, growth stage, type of herbicide and its dose. Among the tested weed species, <i>S. media</i> showed the weakest reaction to the herbicides used and it was only slightly affected by herbicide rate and growth stage. Later herbicide treatments, when the weeds reached the stage of 6-8 and 10-12 leaves, resulted in diversification at the level of herbicide effects and doses.
Highlights
It is well known that the full recommended dose of herbicide is appropriate for farming practice to ensure a good level of weed control and prevent yield loss
Reduced rate applications are not always reasonable, because herbicide activity can be affected by some factors related to weeds and crop status such as weed density, weed growth stage, and crop vigour as well as abiotic factors i.e. weather conditions, soil properties etc., and the herbicide effect can be decreased under adverse circumstances
Despite its economic and environmental benefits, this weed control system is not always recommended, because it requires specific biotic, abiotic and agrotechnical conditions for herbicide treatments which ensure the level of weed control not endangering the crop and weakening weed vigour
Summary
It is well known that the full recommended dose of herbicide is appropriate for farming practice to ensure a good level of weed control and prevent yield loss. Previous investigations showed that a good weed control level could be obtained in case of reduced rate application, which is beneficial to the natural environment and economically profitable. The current trend in agriculture is towards a reduction in the amount of active ingredients introduced to arable fields during plant protection treatments. It is aimed at maintaining weed infestation at an acceptable degree that is harmless to crops, rather than obtaining total weed control (Domardzki , 2006; Krawczyk , 2008). A reduction in herbicide rates requires numerous detailed investigations concerning the influence of these factors on herbicide efficacy (Kudsk , 2008)
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