Will the efficacy of an ALOMY treatment with ‘Atlantis’ in spring be reduced by a prior application of ‘Lexus’ in autumn? – Keyword: Conditioning for resistance

Abstract

Currently, there is controversy regarding whether or not an autumn application with the product ‘Lexus’ for black grass control reduces the efficacy of an ‘Atlantis WG’ application in the following spring. It is hypothesized that metabolic resistant ALOMY individuals who survived the first ALS treatment are less susceptible to following ALS treatments through conditioning. To answer this question, which represents the strategy of ALS sequential applications, EpiLogic was requested to apply a suitable experimental design.
For this purpose, black grass plants possessing a measurable metabolic resistance level towards ALS were selected using ‘Lexus’ (40 g/ha) within an ALOMY monitoring program. Simultaneously ‘Atlantis WG’ (500 g/ha) was used to exclude that the respective populations were affected by target-site resistance and/or high metabolic resistance. For the selected populations, ‘Atlantis WG’ showed high efficacy.
The selected plants were transferred to single pots. After different time periods, during which the plants were exposed to specific environmental conditions, and after an appropriate tillering phase, the plants were vegetatively multiplied (plant cloning). Three clones per parental plant were used in three different treatments: Control, ‘Lexus’ (40 g/ha) and ‘Atlantis WG’ (500 g/ha). Parental plants were obtained from several selection experiments and thus several of such sensitivity analysis of respective clones could be performed. The three treatments were investigated under four variants of time and environmental conditions. All experiments were conducted in a climate chamber under controlled environmental conditions. Only the plants of variant four were exposed to overwintering in the field which lasted approx. 3.0 to 3.5 months.
The assessed data of the clones from the parental plants are compared to the data obtained during the selection assay. The experiments demonstrate a uniform picture across all herbicide applications and environmental conditions. For plants which survived a ‘Lexus’ treatment due to their metabolic resistance, no measurable conditioning for resistance occurs within the ‘Lexus’-‘Atlantis WG’ sequence. Therefore, the application of ‘Lexus’ in autumn does not result in a resistance-increasing effect to the application of ‘Atlantis WG’ in spring. Additionally, the application sequence ‘Lexus’-’Lexus’ revealed that even a slight decrease in sensitivity can be excluded for respective plants.