Wet summer prompts warning
Last summer was probably the worst sheep blowfly season for nearly 20 years according to Livestock ealth and Pest Authority district verterinarian Dan Salmon, who is hoping to avoid a repeat.
To be sure, he said there are a few lessons we should learn.
Dr Salmon said although a repeat of last year is unlikely, the forecast of another wet summer should make producers think seriously about how they are going to manage sheep blowflies.
‘‘One thing that we learnt last year was very few of the problems were due to chemical resistance,’’ he said.
‘‘The chemicals which have been working for the past thirty years still work, and the chemicals which have not worked properly for the last thirty years still don’t work.
‘‘New chemicals work, although some of them are not as good as their manufacturers would like us to think.
‘‘There are some good chemicals available for sheep blowfly control, but none of them are perfect and all of them require a certain amount of management to get satisfactory results in a bad fly year.’’
For instance, Dr Salmon said cyromazine still works as well as it did in 1972 but heavy rain such as we saw last summer will wash it out of the wool and allow flystrike.
Dicyclonil is extraordinarily effective against flystrike, he said, but it has a very long with-holding period so that it has to be applied with a view to when the sheep will be shorn or slaughtered rather than waiting for blowflies to become active.
‘‘If a producer is going to use dicyclonil use it early, that way the flies will never get a chance to build up,’’ he said.
‘‘There are good chemicals available to control blowflies and with the current good sheep prices the payoff is good, but trying to treat sheep in the middle of a fly-wave is a lot harder and less effective than taking a preventive approach.’’
Contact your local LHPA office for more information about blowfly prevention.