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New Zealand Plant Protection 67 (2014): 331

Have wild oats in Canterbury become resistant to herbicides?

K.C. Harrington and R.J. Chynoweth


To investigate rumours that herbicide resistance has developed in wild oats (Avena fatua), seeds of this species were collected from eight arable farms (either one or two populations per farm) in Canterbury from which possible resistance to either fenoxaprop-P-ethyl or haloxyfop had been reported. Seeds were also obtained from two properties where no resistance was thought to exist. Seeds from these 14 populations were germinated using dormancy-breaking techniques and established individually in pots within a glasshouse in October 2013. When seedlings were 4 weeks old, they were sprayed with the recommended rate of fenoxaprop-P-ethyl, haloxyfop or flamprop-M-isopropyl. None of the populations were controlled adequately by flamprop-M-isopropyl because insufficient competition was exerted on the seedlings following application as required to make this herbicide work well. One of the 14 populations was poorly controlled by all three herbicides, suggesting it has developed resistance to these herbicides. The remaining populations were adequately controlled by fenoxaprop-P-ethyl and haloxyfop. However, seedlings of one of these susceptible populations were not treated with fenoxaprop- P-ethyl until they were 6 weeks old and these were not controlled, showing the importance of applying this herbicide early enough while seedlings are still susceptible.

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