"In recent years we've seen more crop damage - especially on soybeans - from herbicides," says Bill Johnson, University of Missouri-Columbia (UMC) weed control specialist. "There are several causes, but many times spray tanks had not been cleaned properly before soybean herbicides were applied."

With more postemergence weed control in both corn and beans and herbicides that are active at lower rates - good cleaning and maintenance of spraying equipment becomes more important than ever.

"It's critical with broad-spectrum products such as Roundup or Liberty," says Bill Casady, UMC ag engineer. "Even a small amount of herbicide left in the sprayer system can cause serious crop injury."

In fact, sprayer contamination can cause crop damage several months later, if a sprayer has not been cleaned well.

"Even if you'll be using the same chemical the next day, flushing a sprayer with clean water is a good idea," says Casady. "Try to end the day with an empty sprayer and refill it with fresh water. Chemicals can settle to the bottom overnight; some cause rapid corrosion."

Most custom applicators have secondary containment and a concrete apron where they clean equipment, reports Terry Knipmeyer, with Riggins Co., a spray equipment dealer in Marshall, MO. "They catch the rinsate and reuse it the next time they're mixing chemicals for that same crop. Not all farmers can afford that kind of setup, but it can save material for producers who spray a lot of herbicides."

For farmers who don't, the quickest and easiest way to rinse a sprayer and dispose of the rinse water safely is to carry along a drum or tank with 50 or 100 gallons of fresh water. When you're finished spraying, flush the sprayer in the field and spray the rinsate on the crop you have been spraying, says Casady.

"Even if you've emptied the sprayer, you'll have a gallon or two of material in the system," he adds. "But if you dilute that with 100 gallons of clean water, that reduces the concentration to only 1% of the original spray mix. Remember, though, that you'll still have some full-rate product in the lines, so you need to spray the rinsate where you aren't going to do any damage."

Between crops and at the end of the season, a more thorough cleanup is required. Casady recommends first filling the tank half full of fresh water, then flushing the tank, lines and nozzles for at least five minutes.

"Owning a good tank-cleaning nozzle is important," he says. "You need something to give you 360 degrees of high-pressure spray inside the tank. Most nozzle manufacturers have them, such as the TeeJet 27500E-TEF rinsing nozzle."

After thorough rinsing, refill the tank with water and add a commercial tank-cleaning agent (check the herbicide label for recommended tank cleaners). You can make your own by adding 2 quarts of household ammonia per 50 gallons of water.

"Or you can use 4 lbs of trisodium phosphate detergent per 50 gallons of water," says Casady. "Operate the sprayer long enough to make sure boom lines and nozzles are filled with the cleaning solution. Then let the solution stand in the system for several hours - preferably overnight. Agitate and spray the solution onto a safe area."

Remove nozzles, screens and strainers and wash them separately in cleaning agent and water. Then replace everything, rinse and flush the system once more with fresh water.

If you can, rinse the sprayer with clean water in the field and spray the rinsate on the crop you have been spraying.

"Check the herbicide label for any special rinsing instructions," says Casady. "And don't overlook a step. Good cleanup is more a matter of discipline than of technology. The idea is to head off problems before they happen."