If all you do is look at the photos below, you will learn what you need to know. You may have seen them before, but they are worth looking at again. They tell a powerful story.

These photos show what happens if you finish spraying one chemical and switch to another chemical to spray over a crop that is sensitive to the first chemical — and you don’t follow the clean-out procedures recommended on the herbicide label. There will likely be enough residue left to cause damage.

Following the triple-rinse procedure is important, says Fred Whitford, Purdue University Pesticide Programs. It’s not all that needs to be done to clean out a sprayer, but it’s an important step. Whitford studied sprayer clean-out and prepared Extension publication PPP-108, "Removing Herbicide Residues from Agricultural Application Equipment."

Pete Illingworth is familiar with the procedures Whitford outlines in the publication. Illingworth, an employee responsible for spraying at Purdue's Throckmorton research center, practices triple rinsing every time he switches chemicals.

Here are three examples from PPP-108 that show the value of triple rinsing.

• Rinse water from the first rinse still contains a considerable amount of herbicide residue. There will likely be enough residue left to produce stunting and cupping in sensitive plants. If the residue is glyphosate, for example, it can produce symptoms if sprayed on non-Roundup Ready beans. Recommended practice is to spray rinse water back over the crop. Make sure you spray it over the crop you just sprayed, not over a field of potentially sensitive soybeans.

STUNTING AND CUPPED LEAVES: There was still considerable residue left in the first batch of rinse water. It produced stunting and cupping. (Fred Whitford, PPP-108)

• The second rinse still has enough residue to cause some injury. There is enough herbicide residue left in the second rinse that it can likely still cause cupping on sensitive plants. There may not be enough residue to cause stunting.

STILL CUPPED: Note cupped leaves on these plants where the second rinse water was applied. There wasn’t enough residue left to produce stunting. (Fred Whitford, PPP-108)

• Third time is the charm when it comes to rinsing out the sprayer. If you have cleaned the sprayer properly and used the triple-rinse method, soybeans should look normal, even if they are sensitive to the chemical that was originally in the tank. You shouldn’t see cupping or stunting at this point.

NO STUNTING OR CUPPING: When the third batch of rinse water was applied on sensitive plants, there were no visible signs of damage. (Fred Whitford, PPP-108)