An assessment of the physiological response of weeds to herbicide application

Herbicide application is one of the most widely used weed management tools. Though herbicides are effective at killing plants (specifically weeds), their application can result in variable levels of control, and uptake rates, as well as damage to non-target plants (i.e. off-target damage). The effectiveness of herbicide application in the field is typi- cally assessed using visual estimations of the level of damage observed, either to individual leaves or whole plants, using a series of pre-determined categories (e.g. <25% leaf burn) over time, following application. Such visual assessments can result in inconsistencies and only provide information on the effectiveness of the herbicide application, as opposed to the ability of the target species to tolerate the herbicide. In countless instances, the weed is not killed by the herbicide application, and thus information is also needed on how it responds to being damaged, but not killed. Here, we outline how several commercially available tools can be used to increase rigor into field- based assessments of herbicide effec- tiveness. First, we determined the leaf area using leaf area software, and then used software to differentiate between healthy (green) and damaged (brown) areas/parts of the leaf. By taking repeat measurements of individual leaves over time following herbicide application, we determined the changes occurring on the leaf surface/lamina, as an accurate measure (i.e. proportion of the leaf that is damaged), rather than visual estimates of the change observed. We used addi- tional tools to assess the chlorophyll content, photochemical index, and stomatal conductance of the leaf over time following herbicide application. The results from this trial on four weed species showed that these tools provide greater accuracy for assessing herbicide damage than visual observation alone, especially when combined, as well as how leaf function changes in relation to herbicide damage. Though the use of these tools may not be suitable for many and managers, the use of digital photos and leaf area software is more effective than visual observation and should be considered as a viable alternative.

Cite this article as:

Sea, W.B., Sykes, N. and Downey, P.O. (2013). An assessment of the physiological response of weeds to herbicide application. Plant Protection Quarterly 28(4), 132-8.


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First published online: December 5, 2013