Using a plant bioassay to detect herbicide residue
Soil residual herbicide activity has been investigated since the early 1960s. One objective has been to provide producers with specific re-crop recommendations. Numerous plant bioassays have been developed to meet this need. The Alberta Research Council (ARC) has been providing a bioassay service to detect symptoms consistent with herbicide carryover since 1986. The objective of this paper is to describe our bioassay methodology and to provide basic information arising from our experience. Soil samples suspected of containing active residues are submitted to the ARC. Once the soil sample is received, the target crop and a sensitive species are planted in both the submitted soil and a check soil, known to be herbicide-free. Samples are evaluated for initial severity of symptoms and recovery over time. Symptoms consistent with herbicide carryover were found in 77% of all samples submitted. The most common crop-herbicide type combination requested is canola-imidazolinone. The primary limitation of bioassays is that damage in the bioassay may not reflect yield loss in a producer’s field. However, bioassays are the only risk-management tool available to producers and can detect the presence of residues below chemical detection thresholds.
soil residual activity
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