You already know why you need a properly cleaned sprayer: residue that has been left behind from a previous spray can harm a crop and ruin your next application. The damage might not show up for more than a week, and it usually takes longer to identify that the symptoms and damage patterns are from chemical residue. So how do you know when your sprayer is really clean enough?
It starts with prevention and ends with a complete clean of all parts, while following best practices along the way.
Cleaning a sprayer is a lot like doing the dishes. Using the right detergent, soaking the hard stuff, being thorough, and rinsing properly – they all matter².
It all starts, though, with preventing the problem in the first place.
The main culprits that cause sprayer contamination from the mix itself have the following properties:
- Dry formulation
- Poor water-solubility
- Potent in low doses
- Poor solubility at low pH
Many products in herbicide Group 2 mode of action (MOA) have these properties and are worth keeping a close eye on when tank mixing. Why?
Because most herbicides are weak acids. Problems occur when you involve tank mixing with weak acid herbicides, including glyphosate, but especially those formulated as emulsifiable concentrates (oils, EC). Two problems can occur with weak-acid herbicides:
- The weak-acid herbicide lowers the pH of the spray mix, possibly reducing the solubility of the problematic Group 2s.
- The oily formulation can adhere the herbicide to plastic and rubber sprayer parts such as tanks, connectors and hoses².
Our free downloadable spraying guide has more on common modes of action and how they affect your spray applications.
The best advice on preventing a clean-out problem is to make sure the product is fully dissolved or suspended — and that takes proper mixing technique and time.
Screens and strainers
Once properly mixed, you may still encounter problems with nozzle screens or strainers. Dry formulations require a screen mesh of 50 or coarser (according to product labels), but many sprayers contain 80 mesh screens, some 100 mesh².
All screens should be inspected before, during and after spraying these products. Screen residues cause longer-term contamination, so cleaning them is an important part of the entire process.
Source: Hofman, V., & Solseng, E. (2004). Spray Equipment and Calibration, Agricultural and Biosystems Engineering North Dakota State University.
After spraying, the cleaning process relies on three main steps²:
Step 1. Remove as much of the mixture as possible.
The best way to remove the remainder is to spray it out in the field you’ve just treated. You can overspray some products again, but it’s never a good idea to drain the tank without thinking through how it will drain off.
Step 2. Dilute the remainder as much as possible and use it to clean the boom plumbing.
Next, dilute the remaining mix, using tank cleaning adjuvants like ammonia (this raises the pH and helps remove those products whose solubility benefits from a higher pH) and detergent (this removes the oily layer formed by EC formulations). You can find commercial cleaners that combine these properties in one jug.
Diluting is most effective when done in multiple smaller batches, as long as you can verify you’ve reached the entire surface area of the tank walls. Wash-down nozzles installed in your tank can do this for you.
Here's an example scenario²:
Let’s assume your sprayer has a 150-gallon clean water reservoir. It’s tempting to empty the whole thing into the tank, but let’s calculate the precise diluting power of doing it this way versus in batches:
If we had 10 gallon remainder in the tank and added 150 gallons water, the remainder would be diluted by a factor of 16. After spraying this out, we would then have to refill the rinse tank, if we wanted to do more.
If we rinsed in two 75-gallon batches (add 75 gallons, agitate via wash-down nozzle, spray out, repeat), we would dilute by a factor of 72.
And, better still…
If we did three rinses of 50 gallons each, our final dilution factor would be 216. That’s the same dilution as adding about 2,150 gallons to the first 10 gallon spray tank remainder. It’s also about 14 times better than dumping the whole 150 gallons in at the beginning.
You can improve diluting power by adding a separate clean water pump. Commercial applicators will often introduce clean water to the tank as “rinsate” (the mixture of pesticides diluted by water, solvents, oils, commercial rinsing agents or any other substances) is sprayed out, reducing boom water use even further.
Step 3. Ensure anything that came in contact with the spray mix has been cleaned.
Lastly, pay attention to the things you can’t see: screens, boom lines and boom ends. The total inside surface area of black rubber boom hoses on a 100-foot sprayer with seven sections can be as much as 30-50 square feet (or 3-5 square meters) and this surface can bind residues². This job requires detail: scrub screens, soak boom lines and flush boom ends.
What the Pros Know
- Upgrade to more steel components (tanks and booms). Stainless steel is easier to clean than plastic.
- Flush your boom ends. Traditional ball valves do a decent job, but there are some nozzle body end caps that do it automatically. These inexpensive units eliminate the dead space in boom ends, and as a bonus, bleed air from the lines on the go.
- Have defoamer handy, since adding a surfactant or a commercial cleaner can generate a lot of foam.
- Use a bucket to help collect and clean screens. Drop them right in!
Done well, sprayer cleaning doesn’t have to be unpleasant, difficult or time consuming. And, it certainly results in a better night’s sleep before your next application.
Hofman, V., & Solseng, E. (2004). Spray Equipment and Calibration, Agricultural and Biosystems Engineering North Dakota State University. Retrieved from https://www.ag.ndsu.edu/publications/crops/spray-equipment-and-calibration/ae73.pdf
Wolf, T. (2015). An Easier Way to Clean Your Sprayer.
Retrieved from https://sprayers101.com/an-easier-way-to-clean-your-sprayer/
Ozkan, E. (2016). Selecting the Best Nozzle for the Job. Retrieved from