New Zealand Journal of Agricultural Research abstracts

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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

PDF file of entire paper: medium quality (538K); (scanned from paper original: notes about this process)

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