1. The Impact of Water Quality on Pesticide Performance:
The Little Factor that Makes a Big Difference
Kerry Richards, PhD
University of Delaware
Pesticide Safety Education Program
I like to start the presentation by interacting with the audience.
When was the last time you made a pesticide application and the results were less than what you anticipated?
Today, we will look at a little factor that can make a big difference.

2. Factors that Influence Product Performance
Product Selection
Label instructions
Equipment Calibration
Application Timing
When you were not satisfied with your pesticide application:
Who or what did you blame?
Did you blame the product for non-performance?
Perhaps you thought “I should have used a different product”.
Did you believe the wrong rate was used?
Did I match right rate with the pest?
Did you think the calibration of the sprayer was wrong?
Was my timing not the best for the pest I was trying to kill?
Is the pest even on the label?
All of these are valid considerations to ensure the pesticide application gives you the maximum results.

3. We Also Learn from: Trial and Error University Recommendations
Industry Recommendations
Other Applicators
We learn how to achieve maximum performance from our pesticides from a number of sources. These include our own trial and error. What I call learning the hard way.
University recommendations are a good source when trying to decide between products.
Industry recommendations can be a good source of information, but also keep in mind, their built in bias.
Of course, we talk to other applicators and learn what they have done.

4. What about the Quality of the Water Used to Spray Pesticides?
Over 95% of the spray solution is water!
FACT: Research clearly shows that the quality of water used for spraying can affect pesticide performance!
This is one factor that doesn’t get much attention when it comes to pesticide performance.
Even though water often comprises 95% or more of the spray solution.
Did you know research clearly shows the quality of water used for spraying can affect how pesticides perform.

5. Why is this Seldom Noticed?
Water is viewed as a relatively clean input.
Concise, easy-to-read information on water quality and the effects on pesticide performance is scarce.
So why is it that we seldom notice something as obvious as the quality of water used in the spray tank?
For the most part, water is viewed as a relatively clean input; if it runs clear, we don’t give much thought to its purity.
Concise, easy to read information on how water quality affects pesticide performance is scarce.

6. What Kinds of Problems Can Poor Water Quality Cause?
Interact with product
Reduce solubility of pesticide
Decrease absorption by target pest
These performance issues may not be obvious! We tend to blame other factors!
What kinds of problems can poor water quality cause?
Water quality factors such as acidity and dissolved minerals can interact with the active ingredients also the additive ingredients of the pesticide product.
Poor water quality can adversely influence the pesticide by reducing solubility thus decreasing absorption by the target pest. This alone can cause poor results and the need for re-treatment.
The reduced product performance may not be obvious. In some cases, the influence of water on the pesticide reduces its effectiveness only slightly, but it can be enough that tolerant or tough to control weeds, insects, and diseases are not well controlled.
Sometimes, applicators increase the rate of the pesticide, which will mask the effect of the water on the product’s performance.

7. Checking Water pH is Important!
An overview of water pH
Testing methods
Options to improve the pH of water
Checking water quality is important. Your time spent checking the quality of water used in the spray tank can pay big dividends.
In this presentation we will take an overview of
water pH and how it can affect pesticide performance
the various testing methods available
and the options available to improve the pH of water

8. Acidic or Alkaline?
The pH value describes the acidity (concentration of hydrogen ions) or alkalinity of any solution.
First, what is pH?
As you can see here, pH describes the acidity (the concentration of hydrogen ions) or the alkalinity of any solution. The scale ranges from 0 to 14.
It is important to remember that small changes in the pH scale represent large changes in acidity. For example, a pH of 5 is 10 times more acidic (i.e., contains 10 times more hydrogen ions) than pH 6 and 100 times more acidic than pH 7.
The 10X relationship between the values is the same whether going up or down the pH scale. An example, a pH of 9 is 100 times alkaline than a water solution at pH 7.

9. The pH Scale pH = 0 pH = 1 pH = 2 pH = 3 pH = 4 pH = 5 pH = 6 pH = 7
Acidic
Basic
Neutral
pH = 0
pH = 1
pH = 2
pH = 3
pH = 4
pH = 5
pH = 6
pH = 7
pH = 8
pH = 9
pH = 10
pH = 11
pH = 12
pH = 13
pH = 14
Battery acid
Orange juice
Bananas
Pure water
Some examples of pH of commonly known items (see slide).
Baking soda
Soapy water
Liquid drain cleaner

10. pH Value
Most herbicides, insecticides, and fungicides perform best in slightly acidic water.
A pH of 4 to 6.5
However, some pesticides, such as sulfonylurea herbicides perform better in water that is slightly alkaline.
A pH above 7
When it comes to pH and the affect on pesticide performance, there are some general rules or guidelines. Of course, there are exceptions.
Most herbicides, insecticides, and fungicides perform best in slightly acidic water, that is a pH of 4 to 6.5
One exception to this, the sulfonylurea herbicides perform better in water that is slightly alkaline, a pH above 7.

11. pH Rule
When water pH falls outside of the preferred upper and lower boundaries, product performance can be compromised.
In some cases, the pesticide will precipitate out of solution.
Keep in mind there is a range of pH where the product will perform best. When water pH fall outside of the preferred range, product performance can be compromised.
In some cases, the pesticide will precipitate out of solution.

12. pH Rule pH can influence how long a pesticide product remains active.
The effect of pH usually proceeds faster as the temperature of the water increases.
The pH of the solution also can influence how long a pesticide molecule remains intact. A higher or lower than optimal pH causes some pesticides to begin degrading or hydrolyzing.
When a weakly acidic pesticide is placed in water that is slightly acidic, it stays largely intact. Certain insecticides and fungicides have been shown to break down in alkaline water, and the effect of pH usually proceeds faster as the temperature of the water increases.

13. What Does Half-Life Mean?
The amount of time for one-half of the substance to break down.
Example:
1 to 1/2 to 1/4 to 1/8 to 1/16
100% % % % %
This breakdown of the pesticide is usually measured in terms of half life, that is, the amount of time for one-half of the pesticide to break down.
So for example, if the half life is 1 day, by the end of the first day you would have 50% of the active ingredient remaining.
At the end of the second day another 50% would disappear, leaving you with only 25% of the original amount and so on.

14. What Does Half-Life Mean?
The amount of time for one-half of the substance to break down.
Example: Thiophanate Fungicide has a Half-life of 1 hour (pH of 7)
At application = 100%
1 hour later = 50%
2 hours later = 25%
3 hours later = 12.5%
Another example of what half life means.
The amount of time for ½ of the substance to break down.
Ex: Thiophanate fungicide at pH of 7, half-life is 1 hour

15. Effect of pH on Pesticides
Another example: Flumioxazin Herbicide:
As pH varies, so does the Half-life:
pH 5 = Stable
pH 7 = Half-life of 24 hours
pH 9 = Half-life of 15 minutes
In this table, again some examples.

16. Effect of pH on Pesticides
Common/ Trade Name
Half-life with pH 5
Half-life with pH 7
Half-life with pH >8
Carbaryl / Sevin
did not find data
24 days
1 day
Chlorothalonil / Bravo
Stable
Chlorpyrifos / Lorsban
63 days
35 days
1.5 days
Phosmet / Imidan
13 days*
12 hours
4 hours
Simazine / Princep
96 days
Decreases 
Thiophanate / Topsin
80 hours
1 hour
Captan / Othocide
32 hours
8 hours
10 minutes
In this table, again some examples. Note the tends, as the water becomes more alkaline, the half life shortens.
* At pH 4.5
pH half-life data sources are listed at end of presentation.

17. Effect of pH on Pesticides
Selected Half-life of Common Pesticides
Captan / Orthocide pH minutes
Dimethoate / Cygon pH hour?
Phosmet / Imidan pH minute
Endosulfan / Thiodan pH Unstable? (12 hours)
Malathion / Cythion pH hours? (no data)
More examples

18. How to Combat Alkaline Hydrolysis
Know your pesticide products
Know the pH of your water source
Test regularly
Use a commercial buffering agent
Buffer-X
Buffer
Spray-Aide
Buffercide
How to combat alkaline hydrolysis
Know your pesticide products
Read the label and other information from the manufacturer
Know the pH of your water, test on a regular basis
Use a commercial buffering agent if needed

19. General Rule
The pH also can change the chemical charge of a pesticide molecule, limiting its ability to penetrate the leaf cuticle and reach the site action, hence reducing its efficacy.
General Rule: The other thing pH can do to the pesticide is to change the chemical charge of the pesticide molecule, this can limit its ability to penetrate the leaf cuticle and reach the site of activity, this will reduce its effectiveness.

20. Alkaline Hydrolysis
A chemical reaction that occurs when some pesticides in the presence of alkaline water (pH of 7 or above) degrade or lose their effectiveness.
For every pH point increase, the rate of hydrolysis will increase 10X.
Again, when we look at alkaline hydrolysis, pesticides that prefer an acid pH will quickly degrade and lose their effectiveness in alkaline pH.
Of course, for every pH point increase, the rate of hydrolysis will increase 10 fold.

21. General Rule
Check the label for any recommendations in regards to the addition of water conditioners, additives, or adjuvants.
NOTE: The pesticide label may or may not specify the need for additives!
Again check the label for any recommendations in regards to the addition of water conditioners, additives, or adjuvants.
NOTE: The label may or may not specify the need for additives.

22. Testing Your Water Use a professional lab:
Test for Iron, pH, and hardness?
What is the cost?
How much water to test?
Any special guidelines or containers for collecting and transporting the water samples?
Testing your water.
One of the choices you have is to use a professional lab.
Decide what you would like to test for.
pH, iron, hardness etc.
Find out the cost ahead of time
How much water is needed for the test
Any special requirements needed for the test Ex: special container, how to collect, how to transport etc.

23. Testing Your Water Do-It-Yourself Test Kits: Readily available
Reasonable priced
Easy to use and interpret
Reliable
You can also use do-it-yourself kits
Readily available
Litmus paper from swimming pool supply stores
Reasonable price
Easy to use and interpret
Reliable

24. Testing Your Water Test Meters: Quick Reliable
Finally, test meters are also available.
Slightly more cost upfront, but quick to use and reliable.
Cost is in the $75 to $100. range.

27. Any Questions?

28. Use of this presentation or parts of this presentation is encouraged as long as these credit slides are included.
Overall Reference:
Fred Whitford, Purdue Pesticide Programs. “The Impact of Water Quality on Pesticide Performance: The Little Factor that Makes a Big Difference.” November (
pH Half-life Data Sources:
Howard M. Deer and Richard Beard, Utah State University. “Effect of Water pH on the Chemical Stability of Pesticides.” July (
F. M. Fishel and J. A. Ferrell, University of Florida. “Water pH and the Effectiveness of Pesticides.” (
Mention the resources used in this presentation.
especially the Purdue Publication

29. Use of this presentation or parts of this presentation is encouraged as long as these credit slides are included.
pH Half-life Data Sources (continued):
Graeme Murphy, Ontario Ministry of Agriculture, Food, and Rural Affairs. “Water pH and its Effect on Pesticides.” September (
John Rinehold and Jeffrey Jenkins. “Spray-tank Adjuvants” section in the 2012 Pacific Northwest Insect Management Handbook. (
More resources.