New Zealand Journal of Agricultural Research abstracts
Investigations of how phenoxy-resistant Carduus nutans
biotypes
survive herbicide spraying
K. C. Harrington
D. J. Woolley
Institute of Natural Resources
Massey University
Private Bag 11222
Palmerston North 4442, New Zealand
k.harrington@massey.ac.nz
Abstract Biotypes of nodding thistle (Carduus
nutans)
have developed within New Zealand that require over six times the
normal rate of MCPA, MCPB or 2,4-D to kill them. Radiolabelled 2,4-D
was applied to both resistant and susceptible nodding thistle plants to
investigate the mechanism of resistance. There was no difference in
penetration of the 2,4-D into the foliage of the resistant and
susceptible plants. However some minor differences in
translocation were detected, with the 2,4-D apparently less mobile
within the resistant plants. These differences were variable and
did not fully explain the resistance. Significantly more
radioactivity was released from the roots of susceptible plants. There
were also small but significant differences in the quantities of
radioactivity that could be removed from within the treated plants by
ethanol, suggesting more binding within susceptible plants.
Significant differences were detected in rates of metabolism of 2,4-D
within the root systems. More radioactivity was present as
water-soluble compounds in the resistant plants than the susceptible
ones. Of the ether-soluble components extracted, about 14 times more
2,4-D was estimated to be present in susceptible plants than in
resistant plants, with chromatography suggesting that compounds in the
resistant plants were metabolites of 2,4-D.
Keywords Carduus nutans; herbicide
resistance;
phenoxy; 2,4-D; mechanism of action; translocation; herbicide
degradation
A05039; Online publication date 26 October 2006 Received 19
September 2005; accepted 20 September 2006
New Zealand Journal of Agricultural Research, 2006, Vol. 49:
465–474
0028–8233/06/4904–0465 © The Royal Society of New Zealand
2006
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