Cleaning Spraytanks

The proper procedure for cleaning a spraytank depends on several factors including the composition of the spraytank, pesticides used, and sensitivity of the crop to which pesticides will be applied following the cleaning. In some cases, triple rinsing with water will be sufficient, depending on the herbicide used. Typically, a detergent should be added to the water. Removal of many herbicides from spray equipment requires the use of ammonia or approved tank cleaners. Specific directions are included on herbicide labels; they should be consulted and used.

Some pesticides are more difficult to remove from spraytanks than others. These pesticides often have very low use rates (e.g., Aim and Sandea), or may stick to residues of other chemicals that remain in the sprayer. In some cases, additives such as crop oils or nitrogen solutions may allow the release of previously used herbicides, or enhance the efficacy of herbicides that remain in the tank.

There are numerous recommendations about cleaners for specific herbicides. Cleaners usually fit into the categories of detergents, ammonia, chlorine bleach, or commercial tank cleaners.

Ammonia increases the pH of the solution, which increases the solubility of many herbicides and the potential to remove them from the spraytank. Ammonia is commonly used to clean tanks.

Commercial tank cleaners generally raise the pH of the solution and act as detergents.

Chlorine bleach lowers the pH of the solution, which speeds degradation of some herbicides, but does not improve the solubility of many herbicides. Chlorine bleach is not usually recommended as a cleaning agent.

Never mix ammonia with chlorine bleach; this mixture creates dangerous vapors.

A Standard Triple-Rinse Procedure for Cleaning Spraytanks

1st rinse: Drain remaining pesticide from the spraytank and hose down the interior surfaces of the tank. Then flush tank, hoses, boom, and nozzles with clean water for 10 minutes.

2nd rinse: Fill the tank with water, add detergent or other recommended cleaner (see table), and recirculate for 15 minutes. Spray some of the rinsate though the boom and nozzles, then drain the tank.

Pesticide labels for very-low-use-rate herbicides (such as Aim) or growth regulators (such as Landmaster and 2,4-D) often recommend that the cleaning solution be allowed to stand for a few hours in the sprayer, sometimes as long as overnight.

Remove the nozzles and screens, and clean them separately.

3rd rinse: Drain the cleaning solution from the tank, rinse with clean water, then spray rinsate though the boom. Repeat steps 2 and 3 for difficult to remove herbicides.

Validating Spraytank Cleaning Methods

Sometimes, a bioassay can be used to test whether a spraytank has been thoroughly cleaned. The simplest method is to collect rinsate from the final rinse, then, using a sprayer or spray bottle, apply it to plants known to be extremely sensitive to the herbicide in question, then compare the effects on untreated versus treated plants. For instance, rinsate from a tank holding 2,4-D could be applied to tomato plants. A second option would be to fill the cleaned tank with water, then spray the water on a small area of the crop that will be treated.

The disadvantage of these bioassays is that symptoms will often take a few days to develop; in the case of sulfonylurea herbicides, it may take 2 to 3 weeks. Another drawback is that water and cleaners may not remove remaining residues in the spraytank in the same manner as herbicides and other adjuvants that might be used.

Some herbicides are difficult to completely remove from spraytanks and can cause serious injury to susceptible crops if even minute amounts of herbicide remain in the spraytank. Phenoxy herbicides fit this category because of the damage that herbicides such as 2,4-D can cause to tomato and other plants of the family Solanaceae. It is often prudent to simply use dedicated spraytanks to avoid the risk of injury from residues that may remain from other uses.