With the rain, new problems arise

With the rain, new problems arise

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Copper-based algaecides and herbicides will kill blue green algae, but they can also be toxic for other aquatic life. Photo by Shutterstock.

Copper-based algaecides and herbicides will kill blue green algae, but they can also be toxic for other aquatic life. Photo by Shutterstock.

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Issues that were problems last week are no longer a concern, while new problems have emerged.

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Is Blue Green Algae dangerous?

The wonderful rain that so many received has changed their outlook.

Issues that were problems last week are no longer a concern, while new problems have emerged.

However, sadly, some of us missed out on rain this time.

It reminds me of the bloke who only got 10 points when Noah got 40 days and 40 nights of rain.

Last week one of our main enquiries was about blue green algae (BGA) in dams.

Is it dangerous and what can we do about it?

For the folks to the north and east who were under rain, dams should be flushed and filled, taking care of BGA issues.

For these producers, one of the next issues might be barber's pole worm.

In our area, quite a few people have submitted dam water samples for testing.

Often the samples have been positive for toxic BGA.

So what can we do about this? Unfortunately treating BGA in dams is not simple.

We know that copper-based algaecides and herbicides such as simazine will kill BGA but they can also be toxic for other aquatic life.

Additionally, when the BGA is killed it can release toxins, increasing the risk to stock.

A district veterinarian reported that a year or two ago a producer lost 100 ewes near a dam shortly after he treated it with copper sulphate.

Some treatments including barley straw and alum tie up nutrients in the dam water, making conditions less suitable for algae to flourish.

Another recommendation is to stir and aerate the water by pumping it over rocks or a batter.

Some stock owners have no choice but to allow their stock access to BGA infested dams.

We usually find that experienced stock avoid the algae and drink from other parts of the dam.

We have found over the years that mortality is relatively uncommon given the number of affected dams.

That said, I spoke to a cattle owner recently who found five cows dead close to an affected dam and another producer has lost at least a dozen young ewes from BGA toxicity.

So the risk is genuine and it is best to prevent stock from accessing infested dams.

Battling barber's pole worm

As mentioned, for those people who did get rain, barber's pole worm (BPW) is now a risk.

BPW eggs hatch when it is moist and warm, so conditions are ideal for BPW worm eggs to hatch across many areas.

Many producers, especially from the north of the state, have experience in dealing with BPW but in previous years stock owners in areas where BPW have not traditionally been a problem have been caught, losing big numbers of sheep following unusual summer rain.

However, in many parts conditions have been so dry for so long that the number of worms on pastures will be minuscule and there may also be very few worms inside sheep to start laying eggs.

Soon it will also become too cold in many areas for BPW to hatch.

To avoid either drenching unnecessarily (and promoting drench resistance) or being caught with an escalating BPW problem I suggest doing worm egg counts, including worm type, on several mobs of sheep in the next few weeks.

This test will soon tell you whether your sheep are putting worm eggs out onto pastures with the potential to become a problem.

Please discuss with your local animal health adviser.

Local knowledge is so important in BPW control.

  • Bruce Watt is a district veterinarian with Central Tablelands Local Land Services, based at Bathurst. Email bruce.watt@lls.nsw.gov.au or call 6333 2300.
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