Piehl’s Dye Experiment and Implications for Herbicide Treatment

Are you sure you want to apply herbicide to this plant?I never thought about this when applying herbicide to cut woody vegetation, or even herbaceous weeds, but we should be watching out for nearby parasitic and hemiparasitic plants. Wood-betony (Pedicularis canadensis), for example, taps into relatives of a number of species we’re often trying to suppress or eliminate from ecological restoration projects (e.g., aspen, cedar, honeysuckle, maple, pine, sumac). Martin Piehl’s techniques for studying the relationship between hemiparasites and host plants included tracer experiments where he applied a water-soluble dye to cut trees and watched for its appearance in nearby hemiparasites. “After several days, in the case of the aspen host, a high enough concentration of dye was taken into the leaves of the parasite to cause them to wither and die …” Granted, he was applying a large amount of the chemical. But it is certainly worth keeping in mind. Fortunately, most of the invasive plants I’ve had to apply herbicide to are far from our wood-betony colony.

If anyone has personal experience with this, please let me know. I’d also like to compile a list of parasites and hemiparasites found in Wisconsin. I was actually surprised when I first learned wood-betony is a hemiparasite. There could be another parasite or hemiparasite connected to the honeysuckle (Lonicera spp.) I intend to cut and apply herbicide to later.


Piehl, MA. 1963. Mode of attachment, haustorium structure, and hosts of Pedicularis canadensis. American Journal of Botany 50(10): 978-985.


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