Factors affecting herbicide performance

Sprayer decontamination

There is a risk of crop damage from traces of some herbicides left in the sprayer after treating the previous crop. Using the decontamination process described here will reduce the risk of damage. The potential contaminators are the sulfonylureas (Glean^®, Logran^®, Ally^®, Seige^® and Brushoff^®) and hormone-type herbicides such as 2,4-D, MCPA and picloram. 1% of the recommended rate of these herbicides can cause damage to lupins and pasture legumes.

Chlorine bleach cleaning

This method should be used to remove sulfonylureas and most other pesticides from sprayers.

Chlorine is a powerful oxidising agent and will decompose most organic molecules.

1. To each 100L of water in the tank, add 300mL of 4% bleach, 100mL of 12.5% or 6g of 65% pool chlorine. Agitate and circulate solution through all lines. The sprayer can be run briefly to fill the boom.
2. Let the unit stand for 15-30 minutes, then drain.
3. Repeat step 1. The solution may be left to soak overnight for an especially thorough cleaning.

Alkaline cleaning

This method is recommended after use of acidic chemicals such as 2,4-D, MCPA, dicamba, picloram and triclopyr (e.g., Garlon^® ). The alkaline solution can dissolve these herbicides and if they were ester formulations, strong alkali is able to hydrolyse the molecules, converting them to a water soluble form that is more easily removed. Ester formulations are particularly bad contaminants, because they penetrate rubber and plastic seals and hoses. From there they can be gradually released into subsequent sprays and cause damage.

Water soluble amine formulations

1. Add either 800mL of household ammonia, 250grams (g) of sodium carbonate (washing soda), or 200g of sodium hydroxide (caustic soda) to each 100L of water in the tank. Agitate and circulate the solution through all lines. Run the sprayer briefly to fill the boom.
2. Let the unit stand for two to three hours, then drain.
3. Repeat step 1. The solution may be left to soak overnight for an especially thorough cleaning.

Ester formulations (emulsifiable concentrates)

Proceed as above, but only use sodium hydroxide, not ammonia or washing soda. Also add 200mL of wetting agent.

Precautions

• Chlorine bleach should never be mixed with ammonia. Chlorine reacts with ammonia, destroying the cleaning power of both. Volatile, acrid nitrosamines are formed, which can cause eye irritation.
• Caustic soda solution will corrode aluminium, brass and galvanised parts. These should be removed or isolated from cleaning solutions of caustic soda. Ammonia solutions at the concentrations recommended will not affect these metals.
• Sulfonylureas may be difficult to remove from damaged or cracked fibreglass tanks. Tanks should be repaired and cleaned thoroughly before the start of the spraying season.