Influence of adjuvants and interactions between herbicides and weed species by determination of relative adjuvant-effect on herbicide dose

When adjuvants are used as a partner for herbicides in tank-mixtures, they can have a positive influence on herbicidal efficacy in certain situations. The addition of adjuvants can contribute to an enhanced effect of the herbicide when applying the maximum registered dose or when securing weed control of reduced application rates. The influence of adjuvants depends on weather factors, the herbicide partner and the particular weed species. This study examined the influence of different herbicide-adjuvant-combinations on various weed species. The objective of the study was to clarify, if the addition of an adjuvant to a herbicide leads to comparable results within the examined weed species or if the influence of an adjuvant use varies. The determination of relative adjuvant effects allowed comparisons of the data. The influence of six herbicideadjuvant-combinations on six weed species was evaluated in greenhouse trials. All herbicides used were from the group of ALS-inhibitors (HRAC-group B). Data of the greenhouse experiments were compared to results from field trials, which were conducted at five sites in Rhineland-Palatinate. One herbicide with and without an addition of an adjuvant was applied per site. Data of the studies reveal that the use of adjuvants results in a positive influence on herbicidal efficacy in most cases. However, strong differences in intensity as well as quality of adjuvant effects regarding the response of different weed species were observed. The efficacy of the herbicide BIATHLON® for example was improved by addition of an adjuvant for Galium aparine by a factor 364.56. For Daucus carota this factor was 2.98. Growers should necessarily take account of these differences when using adjuvants, especially when they are used to secure reduced application rates.