ALWAYS water flush the spray system at the completion of mixing or spraying. 

One of the most critical steps in reducing the level of residue in the tank, pump and plumbing is to ensure the sprayer and mixing equipment are completely clean after use. Thoroughly flush the mixing and transfer system with water as soon as mixing has taken place, and flush the spray equipment with clean water immediately after spraying has been completed. Delaying the water flush by even an hour can more than double the amount of product that may bind to tank linings, hoses and other fittings. 

Most products will require further cleaning and decontamination using an appropriate cleaning agent, even after the water flush has been completed. 

There are a range of commercial cleaning agents available for decontaminating spray equipment. It is essential that spray operators refer to product labels and manufacturers’ technical information to ensure the correct cleaning agent is used. Always ensure that chlorine-based products are ‘fresh’ and other agents are used before the recommended expiry date. 

Steps in the cleaning process 

Step 1: Select a suitable area for the wash-down and cleaning process Cleaning the sprayer can present risks to the person doing the cleaning, bystanders and to the environment, through build-up of residues in the soil or from run-off into water courses. Always use appropriate personal protective equipment (PPE) and select an area that is well grassed, where run-off from the washing process cannot 

enter water courses. It is useful to identify several appropriate locations on the farm so that the cleaning site can be moved to prevent the build-up of residues in the soil.  

Step 2: Remove external residues from the sprayer before starting 

If booms and nozzle bodies are covered in dust and chemical residue, pressure- wash the boom, nozzle and filter bodies and tank exterior before starting the decontamination. 

Step 3: Immediate water flush Knockdowns 

Start with an empty tank. Plan ahead for the final load of any spray job by only mixing as much product as is required for that load. As soon as spraying has stopped, complete an in-field water flush and spray out the remaining contents of the tank onto a suitable fallow paddock. 

Residual herbicides 

Residual herbicides pose a significant risk to future crops and the environment so require special attention to minimise those risks.

It is still critical to conduct an in-field water flush, however disposing of the diluted product may present a significant risk when compared to other products with little or no residual effects. 

If the operator has a dedicated disposal system then tank contents should be drained into this. However, the majority of growers still don’t have these facilities, so an alternative strategy needs to be used. 

The most common approach to disposal of tank contents after the water flush has been completed is to spray them out onto the paddock where the original mix has just been applied, provided the application will not exceed the maximum registered rate for the product and the plant-back period will not be significantly affected.  

Step 4: Pre-clean the spray system and mixing equipment with water 

Pre-cleaning is an additional step to the in-field water flush and is important to dislodge any built-up residues from the spray system and tank. In some instances where salt or amine formulations of phenoxy-type products (Group 4) and some suspension concentrates have been used, it may be necessary to add a softening agent (usually cloudy ammonia, unless cleaning with chlorine bleach as the cleaning agent) to help remove hard or stubborn residues. 

Add clean water to the tank to about one-quarter to one-third of the full capacity, and add the softening agent where appropriate. Run the solution through the lines and nozzles for about two to three minutes, then, with the nozzles turned off, run the sprayer agitation and tank-rinse nozzles at the same time for at least 15 to 20 minutes. 

Spray out the tank contents onto an appropriate field or fallow area and drain the tank completely at the selected cleaning site. 

Inspect tank and spray system for any residue remaining on ledges and sumps. Pressure-wash with clean water (ensuring correct PPE is worn) and flush and drain the tank at the selected cleaning site. 

Step 5: Use cleaning agents (where recommended), or complete this step with clean water for those products not requiring a cleaning agent for decontamination 

Add enough of the recommended cleaning agent(s) to clean a full tank. If products were mixed using an induction hopper, add the cleaning agent and some fresh water through this system. Where a separate mixing vat was used, decontaminate this system separately from the sprayer. 

Add enough clean water to fill the tank to about one-quarter to one-third of the full tank volume. Agitate the mix and run the solution through the lines and nozzles for about two to three minutes, then, with turned nozzles off, run the sprayer agitation with the cleaning agent for at least 15 to 20 minutes. If a tank-rinse nozzle is fitted, use this at the same time. 

Remove and clean nozzles, drain filter bowls, and remove the filters and o-rings. Remove the diaphragm from non-drip nozzle bodies. Clean the fittings, nozzle bodies and other areas where components have been removed. 

Soak o-rings, filters, diaphragms and nozzles in a separate bucket with the cleaning agent for at least 15 to 20 minutes. Rinse with water, then clean again with warm soapy water. Inspect all items then rinse again with clean water. 

Tip

Do not leave plastic nozzles in chlorine (bleach) solutions for more than half an hour, as some may become brittle.

Fill the tank with clean water (in addition to the water and cleaning agent already in the tank) to the point of over flow, close the lid and ensure it is in contact with the tank contents. Allow this to stand for several hours, preferably overnight. Fill the induction hopper to the point of overflow and also allow this to soak for the same period of time. 

After soaking for an extended period, drain the induction hopper and flush with clean water. Agitate the tank again for 5 to 10 minutes, then flush the lines with the contents of the tank (water and cleaning agent), run the boom one section at a time, with the end tap open. Turn the boom valves on and off several times to ensure they are working and cleaned. 

Replace all o-rings, filters, diaphragms and nozzles. 

Spray out any remaining contents of the tank (to a previously unsprayed fallow area). 

Step 6: Inspect the internal surfaces of the tank 

If residues are still found on ledges and other areas of the tank, use a pressure washer to remove these and allow the contents to completely drain. 

Repeat step 5 again, then move to step 7. 

Repeating step 5 is particularly important for many Group 2 herbicides (especially sulfonylureas) and some other pre-emergent products, suspension concentrate formulations, some Group 1 herbicides and especially for Group 4 herbicides. 

Step 7: Final water rinse – internal 

Once the tank is clean, fill the tank to about one-quarter to one-third of its capacity with clean water and repeat the high-pressure flush of the whole boom, followed by flushing individual sections one at a time. 

Check nozzle patterns while flushing with clean water, note and replace any with a poor spray pattern or changed flow rate. 

Drain the water and rinsing from the tank onto a well-grassed area, ensuring run-off cannot enter a water course. 

Rinse with clean water, flush the spray system and completely drain the tank and system. 

Step 8: Final clean – exterior 

Use a pressure washer to clean the exterior of the sprayer and booms to remove any remaining residues and dirt from the entire spray rig.