Water hardness may cause pesticide molecules to bind to minerals. The wrong pH may cause products to degrade. Both can reduce control.
Fred Whitford has a challenge for you. And it could help you improve your pest and weed control every time you spray.
"Testing water hardness and pH, and adding a water conditioner if needed, improves the effectiveness of herbicides, insecticides and fungicides," says Whitford, Purdue University’s coordinator of pesticide programs. "It results in faster, more complete, longer-lasting control, with less chance of having to re-treat or of developing resistant pests."
Unfortunately, there has been little third-party or university research on the potential benefits of water conditioners in chemical application procedures.
"But the anecdotal evidence of improved control is almost overwhelming," Whitford says. "We’re hearing reports from everyone who uses pesticides—from farmers to lawn care experts to specialists in roadside maintenance. They all tell us that water conditioners make a tremendous difference."
Basic logic also indicates that those anecdotal reports are correct. Whitford explained why to the attendees at this past summer’s Farm Journal Corn College.
"Water hardness and acidity can interact with active ingredients or additives in pesticides to reduce control," Whitford says. "They also can reduce solubility and decrease absorption by a pest."
Water hardness. Calcium, magnesium and iron molecules will bind themselves to some pesticide products.
"The most common example is glyphosate becoming tied up with calcium and magnesium," Whitford explains. "That’s why we add ammonium sulfate to the spray tank when using glyphosate—to prevent this binding action."
When pesticide particles get bound up with minerals, the active ingredient may be unable to enter the pest. It may enter more slowly, or even precipitate out of the solution. "The more pesticide that is bound to minerals, the more diluted the product becomes in your tank," Whitford says.
The chemical characteristics of a pesticide may change when it becomes bound to a mineral, Whitford continues. "The pesticide may not dissolve in water, penetrate leaf tissue or attach to the site of activity in the pest," he says.
Carrier pH. The acidity or alkalinity of water—measured by pH readings—also affects product performance. The process is almost the opposite of the minerals’ binding action.
"Using water of the wrong pH can cause pesticides to ‘crack,’" Whitford explains. "You can call it neutralizing, deactivating or breaking down—the effect is the same. This is the reason we use ammonia, which is highly alkaline, to clean pesticide tanks—it breaks down the pesticides, so no chemical residues are left.
"Most herbicides, insecticides and fungicides perform best in slightly acidic water, with a pH of 4 to 6.5," Whitford continues. "The main exception is sulfonylurea herbicides, which work better in water that is slightly alkaline, from above 7 to around 8."
If water is outside the preferred pH range, a pesticide may fall out of the solution ratio, degrade or break down. Water pH can even change the chemical charge of some of the pesticide’s molecules. That limits the product’s ability to penetrate leaf cuticle, reducing its effectiveness.
- March 2011