The effects of picloram on Sphagnum fuscum (Schimp.) Klinggr. in peatlands traversed by electrical transmission lines in Manitoba
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Date
1989
Authors
McInnes, Donelda E.
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Abstract
Picloram herbicides (trade name Tordon) are used by Manitoba Hydro for brush control within rights-of-ways through peatlands. A time series study compared the effects of Tordon 22K on Sphagnum fuscum at three peatland sites, a) a string fen bog complex typified by Black Spruce/Ericoid/Sphagnum association along a transmission corridor at Sprague, b) an uncleared mature bog at Elma with similar associations and c) a mature bog which borders a transmission corridor at Devil's Lake. Three concentrations of Tordon 22K (2.2 kg/ha, 1.1 kg/ha and 0.55 kg/ha) were applied and the effects recorded. Crankwires and chlorophyll content were used to monitor the relative growth of S. fuscum during treatments. The results indicated the environmental conditions such as water table levels, rainfall and amount of shading influence the effectiveness of picloram in eliminating Sphagnum species from the habitat. Conductivity observations were used to obtain a better understanding of how picloram was affecting Sphagnum by measuring the slow leakage of electrolytes from actively metabolizing capitula. Culturing techniques were used to illustrate how picloram affected the capitula of the Sphagnum causing extensive expansion until no recognizable capitula remained. Algae, associated with Sphagnum colonized the surrounding agar medium. Micrographs of the treated branches from the capitula illustrated how picloram caused morphological defects in the growing tips of the moss similar to susceptible vascular plants. Picloram is an extremely persistent herbicide and may cause unacceptable ground water contamination and/or the elimination or reduction of non-targeted plant species. Therefore it is important to determine the parameters affecting the persistence of the picloram in peatland soils. A technique was developed to detect picloram residues using a high pressure liquid chromatograph. The results indicated that humic substances in the peat interfered with detection even though traces of picloram residues were detected in peat one year after application. Picloram has a adverse effect on Sphagnum fuscum and remains in peat soils for an undetermined length of time. The drying effect and the removal of the susceptible species changes the natural succession. This is desirable from a management point of view in producing a vegetation community which does not interfere with the transmission of electricity and allows ready and easy access for maintenance.