Be water wise before you spray

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At this time of year, the Department of Agriculture and Food (DAFWA) gets plenty of calls from people asking whether they can use dam or bore water to mix with pesticides (herbicides or insecticides).

Generally, the answer is ‘Yes’, but it depends on which chemicals are being used and what the water quality is like. The following is a list of water quality factors that can cause problems with some pesticides.

Hard water

Hard water is linked to the presence of large amounts of dissolved minerals. These can interfere with pesticides by the process of inactivation, breakdown or precipitation (the chemical falls out of solution and settles at the bottom of the tank).

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Products such as ammonium sulphate or prepared liquid formulations are available to soften hard water.

You can test to see if your water is hard by using a bar of soap and seeing how easily it lathers. This is not an exact test, but if you are not creating many suds, it will give an indication of a problem.

Saline water

Saline water contains high levels of sodium chloride (NaCl). As with hard water, saline water can interfere with chemicals through inactivation, breakdown or precipitation.

To reduce the effects of salty water, mix with other water sources. You can taste water to get an idea of any salinity problems; if your water tastes salty, DAFWA can test water salinity and pH at a cost. Contact your nearest office for more information.

Water pH

As a general rule, pesticides are more stable at a neutral pH of 7.0. Highly alkaline (high pH) water may cause some pesticides to undergo hydrolysis (large molecules are divided into smaller ones, rapidly degrading the pesticide).

For this reason, some herbicides and insecticides should not be left in the tank overnight.

Scheme water or water that has been stored in concrete tanks may be alkaline. One group of chemicals, sulfonylurea herbicides, will break down more quickly in acidic (low pH) water.

Measure your water pH with a cheap pH meter, pool-testing kit or contact the department for locations where you can take a sample for testing. Muddy water

Muddy water usually contains suspended clay or silt particles that can absorb and bind the active ingredients in some herbicides, especially glyphosate and Spray.Seed. The general rule of thumb is that if you cannot see a coin at the bottom of an eight-litre bucket, the water is too muddy.

Particles can be removed by treatment with lime or alum, which settles out the particles so they sink to the bottom. Dirt also blocks nozzles, lines and filters and reduces spray equipment life. Settling out of water should be done to the main supply tank or can be done in the spray nurse tank, but not the boom tank.

Water temperature

High water temperatures can accelerate the process of hydrolysis.

Cold water can result in gelling problems — that is, chemicals do not mix as well in cold water. This can be overcome by agitating the mix.

For more information, contact the Small Landholder Information Service on 9733 7777

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