Know Your Water

March 12, 2011 07:14 AM
Know Your Water

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.

In addition, pH may affect how long it takes for a product to break down and lose its effectiveness. That period is called its half-life. "The effect of pH on a product’s half-life can be dramatic," Whitford says. "A product might have a half-life of two minutes at pH 9, compared with a half-life of 10 hours at pH 5."

Just because treated municipal water is safe to drink doesn’t mean it’s an ideal carrier for spray applications, Whitford adds. "Products that municipalities add to water often shift pH into the alkaline range, typically 7.8 to 8.5," he says.

Test on your farm. Here’s how to find out if water quality issues are hindering your pesticide performance:

"Ask your retailer specifically what is the optimum water pH and hardness for each product you use," Whitford advises. "Then go to a department store, aquarium shop or swimming pool supply house and buy a water test kit. It will tell you the hardness and pH of your water."

The kits, which utilize litmus paper strips, usually cost only $4 to $15, but they are very reliable, Whitford says. They contain enough litmus paper to last most growers an entire crop season.

When the crop conditions are right and you’re ready to spray, mix the water and product in your tank. Then measure the pH and hardness of the solution. "Use the information from your retailer to see how your water measures up as a pesticide carrier," Whitford says.

If a water conditioner is needed, apply one that is recommended by your dealer. "These products cost only 60¢ to $2 per acre," Whitford says. "You dealer won’t jeopardize all the business you do with him by selling you a product that doesn’t work.

"Buy $100 worth of water conditioner and apply a few tankfuls of product with and without the conditioner. The ideal test situations include low-rate products, where you apply only an ounce or so per acre; fields with hard-to-control or resistant weeds; and when you are applying less than full rates of pesticides."

Observe the results. "There will be cases where spending a few dollars on these products will be very beneficial, by helping you maximize the return on the money you spend on pesticide products," Whitford says.

"I’d like to hear how your test turns out," Whitford concludes. "Your experience can help me and others in Extension fine-tune our recommendations for growers." You can share your results by e-mailing Whitford at

Sediment in Carriers Can Reduce Control

Sediment in your water, like hardness and acidity, can reduce pesticide performance, says Purdue University pesticide programs coordinator Fred Whitford.

"If water contains sediment, pesticide particles may bind to the suspended solids, preventing uptake by pests," Whitford says. "Some products contain warnings against mixing them with muddy or murky water from ponds or ditches."

Some pesticides are more likely than others to get bound up with sediment and organic matter in spray solution. "Pesticides have indexes called the soil sorption coefficient [Kd] and the soil organic carbon coefficient [Koc]," Whitford explains. "Those coefficients reflect how strongly the pesticide binds to soil particles and to particles suspended in water. You can obtain these values from pesticide manufacturers."

Letting a sample of your water stand in a glass jar and seeing how much sediment settles out will indicate whether suspended solids are a problem in your water source.

Acidity Guidelines For Pesticide Carriers

The University of California–Davis, offers these guidelines for managing the pH of pesticide carriers:

  • A pH between 3.5 and 6 is satisfactory for most spraying and for storing for 12 to 15 hours in a spray tank. However, sulfonylurea herbicides require a slightly alkaline carrier, with a pH of above 7.
  • A pH between 6 and 7 is adequate for immediate spraying of most pesticide products. But don’t leave the spray mixture in the tank for more than one or two hours.
  • Most products mixed in alkaline water should be sprayed immediately.

Avoid Compatibility Problems When Mixing

"Careless tank mixing can lead to reduced pesticide performance, even if you’ve used a water conditioner, calibrated your sprayer and done everything else perfectly," says Fred Whitford, pesticide programs coordinator for Purdue University.

"Generally, you should run water into a clean tank and then add pesticides in this order: wettable powders and dry flowables; liquids and flowables; emulsifiable concentrates; microencapsulates; and, finally, surfactants," Whitford says. "Agitate the wettable powders and dry flowables before you add the other products."

If you are ever in doubt, mix small samples of the products in a jar to see if they are compatible or not. "Many labels offer specific advice on how to do jar tests," Whitford notes.

Don’t mix two pesticides with different water pH requirements, such as sulfonylurea herbicides and most other products. "Accommodating one will diminish the performance of the other," Whitford warns.

"If you have to mix two such products, decide which one is most important. Make the water ideal for that product to maximize its performance. Use the full rate of the other product, and apply as quickly as possible after mixing," Whitford says.

Corn College 3More Events to Make You More Bushels

Head to the field with Farm Journal Agronomists Ken Ferrie and Missy Bauer. In response to reader and attendee requests, we’ve added new trainings to our event lineup. Be sure to sign up early!

Corn College "Classic"

near Bloomington, Ill.

  • Retailer/Consultant Session
    Monday, July 18
  • Two-day Session for Farmers
    Tuesday and Wednesday, July 19 to 20
  • Two-day Session for Farmers
    Thursday and Friday, July 21 to 22

Corn College "Fundamentals"

Coldwater, Mich.

  • Two-day Session for Farmers
    Wednesday and Thursday, Aug. 3 to 4

For details and to register, go to or call (515) 254-0289.


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