Why mix drenches and adopt annual rotation?
Two effective methods of slowing the development
of drench resistance are combining drenches and
drench rotation. The more effective a drench is
when used in combination, the greater the effect
of delaying resistance. Growers shouldn't wait
until a drench starts to fail before using it in
combination.
Experts agree that it is more effective
to use a combination of two or more effective drench
families than using these drenches on their own
sequentially. Modelling studies have demonstrated
that combining two or more drench families in one
treatment can significantly extend the effective
life of drench families. (Barnes EH, Dobson RJ,
Barger IA. Worm control and anthelmintic resistance:
adventures with a model. Parasitol Today 1995;
11: 56–63.)
Furthermore, given the increased reliance
on the ML drenches and the fact that resistance
is developing to this group, experts agree that
if an effective combination that does not contain
an ML is available, it should be alternated with
combinations containing an ML. (Dobson et al. Australian
Vet Journal, November 2001.)
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