Integrating Selective Herbicide and Native Plant Restoration to Control Alternanthera philoxeroides (Alligator Weed) Page: 30
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tested single triclopyr applications. Two herbicide applications were required to reduce
cumulative stem length beyond controls. After two applications, 50% of treatment pots had no
stems present, whereas after one treatment, 100% of pots had stems present. These results
suggest that although one application reduced stem density of above ground parts, elimination of
stems and leaves required two applications.
Literature points to poor herbicide translocation to roots as a reason for low herbicide
efficacy with A. philoxeroides treatments (Sainty et al. 1998, Julien et al. 2004). Bowmer et al.
(1993) reported that only 7% of glyphosate herbicide applied to A. philoxeroides via foliar
treatment reached the root system. We observed significant root reduction after both herbicide
applications frequencies, but this effect may not have been a direct result of root mortality due to
triclopyr. The shoot/root ratio is a measure of how a plant is allocating resources. The 'functional
equilibrium' theory suggests that a plant will shift resource allocation between roots and shoots
to aid in acquisition of resources that are most limiting (Brouwer, 1962). Experiments involving
pruning of roots and shoots have demonstrated that plants will grow toward a specific shoot/root
ratio over time after a disturbance (Alexander and Maggs 1971, Poorter and Nagel 2000). The
reduction of root biomass we observed could be attributed to a reallocation of plant resources
from roots to shoots due to disturbance of above ground parts via herbicide. Only a snapshot of
the plants' recovery and subsequent shoot/root partitioning was observed because the
experimental design called for a single harvest of all treatments. After one application of
triclopyr, the shoot/root ratio of treatment plants did not differ from controls. A. philoxeroides
that was treated with two applications had significantly lower shoot/root ratios than controls. The
plants exposed to a single treatment may have had enough time to reach functional equilibrium at
the cost of some total biomass, whereas the plants exposed to two treatments did not.
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Adams, Justin. Integrating Selective Herbicide and Native Plant Restoration to Control Alternanthera philoxeroides (Alligator Weed), thesis, December 2011; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc103280/m1/37/: accessed July 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .