New Zealand Journal of Agricultural Research abstracts
Relative intra-species competitive ability of nodding thistle biotypes with
varying resistance to the herbicide 2,4-D
K. I. BONNER
A. RAHMAN
T. K. JAMES
K. S. NICHOLSON
D. A. WARDLE*
AgResearch
Ruakura Research Centre
Private Bag 3123
Hamilton, New Zealand
*Present address: Landcare Research, P. O. Box 69, Lincoln 8152, New
Zealand.
Abstract Resistance of pasture weed species to phenoxy
herbicides is emerging as a potential problem in New Zealand and is especially
apparent in the case of nodding thistle (Carduus nutans). We selected
eight biotypes of nodding thistle known to differ in resistance to the
herbicide 2,4-D and evaluated their relative competitive abilities during
vegetative growth in terms of their effects on growth of the other biotypes,
growth response to the other biotypes, and growth and seedling emergence
responses to pre-established swards of perennial ryegrass (Lolium
perenne). Although biotypes differed in terms of competitive ability for
each of these measures, there was no detectable agreement between any pair of
measures across the eight biotypes. None of the measures of competitive ability
was significantly correlated with herbicide resistance across the biotypes. Our
results show no clear causative relationship between competitive ability as
measured in this experiment and herbicide resistance. Since resistant
populations are apparently of comparable competitive ability to susceptible
ones, cessation of herbicide use is unlikely to be followed by a significant
loss of resistant individuals from a population.
Keywords Carduus nutans; competitive ability;
herbicide resistance; nodding thistle; phenoxy herbicides
New Zealand Journal of Agricultural Research, 1998, Vol. 41: 291-297
0028-8233/98/4102-0291 $7.00/0 (c) The Royal Society of New Zealand
1998
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