Integrating Selective Herbicide and Native Plant Restoration to Control Alternanthera philoxeroides (Alligator Weed) Page: 31
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Competitive influence of introduced plants was limited to effects on A. philoxeroides
shoot/root ratio. Only one species, Justicia american, reduced A. philoxeroides shoot/root
significantly over controls. Competition between plants can affect biomass allocation. Gersani et
al. (2001) found lower shoot/root ratios among soybeans that experienced intraspecific
competition than those that did not. Shortly after transplanting at the end of September, existing
above ground parts of both sprayed and un-sprayed Justicia withered away to no observable
living tissue, before exhibiting minor regrowth at the time of harvest in April. Any competition
between A. philoxeroides and Justicia must have occurred below ground. Resource availability
in the absence of plant to plant interactions has the ability to effect plant biomass allocation
(Wilson, 1988). Plant species respond differently to competition, but these competitive responses
are also altered by abiotic factors, particularly nutrients (Wilson and Tilman, 1995). Introduction
of Justicia may have diminished nutrients in shared treatment pots enough to prompt a biomass
re-allocation response from A. philoxeroides. In addition to resource mediated competition,
plants can interfere with one another below ground through allelopathy (Mahall and Callaway,
Results from the field component did not suggest any reduction in A. philoxeroides cover
after the integration of introduced competitor plants and triclopyr applications. The herbicide
applications alone resulted in reduction, but as in the greenhouse study, introduction of
competitors resulted in little effect. Alternative herbicide timing may have resulted in different
results. Allen et al. (2007) found that a high rate of herbicide applications in April for A.
philoxeroides resulted in increased native plant biomass within the treatment year over July
applications. Allen et al. (2007) proposes earlier applications provided a critical window of
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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/m1/38/: accessed November 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .