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Insects, diseases and weeds, oh my! Keeping these pests at bay on a golf course is a constant challenge, but good results are increasingly achievable with the help of modern pesticides. Still, sometimes pesticides do not deliver the results one might expect. Perhaps the treatment timing was off, or the rate applied was too low? Maybe the product selected is not an effective control option, or a large percentage of the pest population has developed resistance? These issues are often the first things that come to mind when a product comes up short. What is often overlooked, however, is the role that water quality plays.

It should come as no surprise that water quality plays a key role in the effectiveness of an application. After all, the vast majority of a given spray mixture is comprised of water – often more than 95 percent. Despite being such a huge percentage of what is applied to the turf, the water itself often receives little thought when planning an application. Measuring a specific volume during the mixing process to achieve a desired dilution is typically the only attention water gets.    

Superintendents could learn a thing or two from farmers, who routinely adjust the water carrier before adding a pesticide to the tank. This is a simple, low-cost step that can increase the effectiveness of certain pesticides. So, what water issues are farmers trying to overcome and how do they make their water better?

The two main attributes to consider when evaluating water quality that can negatively affect pesticide performance are pH and hardness. 

 

Water pH

Everyone should remember from science class that pH ranges from 0 to 14. A pH of 7 is considered neutral, pH less than 7 is acidic, and a pH greater than 7 is alkaline.

Certain pesticides are sensitive to pH and will begin to break down when they react with water through a process known as hydrolysis (hydro-, meaning “water”, and lysis, meaning “to unbind”). Basically, the pesticide’s active ingredient is broken into smaller molecules and rendered useless. Hydrolysis can occur from the moment a product is added to the spray solution and once a pesticide molecule is broken, it will no longer be effective.

Organophosphorus and carbamate insecticides have been shown to be sensitive to alkaline hydrolysis (Fukuto, 1990). Therefore, if you are going to be using a popular product like carbaryl to control chinch bugs, you will want to ensure that your water pH is below 8. This recommendation is stated within the carbaryl label.

It’s not just insecticides that are at risk for hydrolysis, herbicides like metsulfuron-methyl are also vulnerable. However, unlike the carbaryl example, researchers found that a moderately alkaline pH between 8.2 and 9.4 is not as problematic as an acidic pH of 5.2 to 6.2 for metsulfuron-methyl (Sarmah, 2000). Thus, hydrolysis can occur in basic and acidic solutions, so it is important to understand the unique label instructions for a given product regarding water quality. 

Superintendents need to know any specific water pH recommendations for pesticides they plan to use. Some products might call for the addition of a buffering agent.

Water carrier pH can also reduce the efficacy of commonly used herbicides like 2,4-D, dicamba, and glyphosate, which are weak acids. When such herbicides are mixed in an alkaline water they can become negatively charged and not readily absorbed past the leaf cuticle and cell membrane (Chahal, 2012). Less active ingredient entering the plant reduces the likelihood of delivering a lethal dose and may ultimately lead to poor weed control.

Fungicides are less impacted by water pH than insecticides and herbicides. The only two fungicides that have been reported to be less effective at certain pH ranges are captan and thiophanate-methyl. Captan use in turfgrass systems is quite limited and most superintendents aren’t even familiar with this chemistry. Thiophanate-methyl, on the other hand, has been used in the turf industry for numerous years and is commonly applied for summer patch control.

Savvy superintendents will note that thiophanate-methyl labels have some language about avoiding water carriers with alkaline pH. However, the amount of published data supporting this recommendation is quite limited and based on a single-year study (Fidanza, 2009). Researchers from Purdue University found that pH of spray carrier water had no effect on the efficacy of thiophanate-methyl and metconazole against dollar spot on creeping bentgrass (Stacy, 2020). They did observe a slight reduction in efficacy of iprodione at a pH of 9, but only after it was left in the solution for a period of 24 hours prior to application.

This is an important principle to keep in mind when mixing pesticides. The longer a product is left in solution, the more vulnerable it will be to pH issues like hydrolysis. Every effort should be made to finish an application within a few hours of mixing a tank. Do not store tank mixes of products overnight as they will not work as well. Following this best practice alone could help improve the efficacy of your applications.

The use of pH adjusters can also help, though it is a good idea to consult the pesticide label before adding one of these products to the tank as some pesticides are already formulated to act as a pH buffer. If that is the case, you might not need to add anything at all to address water pH concerns. Contact the pesticide manufacturer should you have any questions as to whether the addition of an adjuvant would be beneficial.   

Another way to avoid pH-related water issues is using a different product that is less affected by pH. For example, switching from 2,4-D amine to a 2,4-D ester formulation can improve performance in high-pH water.

 

Water Hardness

Similar to pH, water hardness can influence the way pesticides perform. Hard water – caused by the presence of dissolved cations such as calcium, magnesium and iron – affects about 85 percent of the country and has been shown to reduce the efficacy of glyphosate and other weak-acid herbicides. The positively charged cations in hard water bind with the negatively charged herbicide molecules, resulting in less-effective weed control.

Fortunately, there is a simple, inexpensive remedy. When ammonium sulfate is added to hard water, it breaks down into ammonium and sulfate. The negatively charged sulfate binds to the positively charged cations in hard water. Conditioning hard water with ammonium sulfate in a sprayer before adding glyphosate, glufosinate, or other weak-acid herbicides can improve uptake and efficacy. 

Adding ammonium sulfate to the spray solution can improve herbicide performance for those dealing with hard water.

A water quality test will help determine whether you could benefit from conditioning the water and exactly how much ammonium sulfate is needed. The components within a water test we want to focus on are sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+) and iron (Fe2+). The amount of ammonium sulfate to add to the tank in pounds per 100 gallons = (0.005 x ppm Na+) + (0.002 x ppm K+) + (0.009 x ppm Ca2+) + (0.014 x ppm Mg2+) + (0.042 x ppm Fe2+).

Water with a hardness of 200 parts per million (ppm) or more should be treated with ammonium sulfate, unless stated otherwise within the pesticide label. As a general rule of thumb, one 51-pound bag of ammonium sulfate per 300 gallons of water is enough to combat issues with hard water. This is a tried-and-true method that has served farmers well for a number of years.

 

Testing Your Water

Water quality testing to determine the most appropriate conditioning steps is a great way to get the most out of your pesticides. Submitting a water sample to your local university extension testing laboratory for analysis is advised. The cost is relatively inexpensive ($35-$55), especially when you compare it to the average cost of a pesticide application. There are also a number of private laboratories that provide water quality testing for the agricultural industry. 

A water quality test is important for understanding the suitability of irrigation water and for determining what steps may be needed to avoid pesticide interaction issues.

Keep in mind that water properties can fluctuate in some areas throughout the year so testing two or three times over the course of the first year might be useful. Once a detailed test is completed, purchase a handheld pH meter if you don’t have one already. This is a great way to double-check the spray tank water immediately prior to mixing a pesticide. You should be able to pick up a unit for $125 or less. Avoid using the paper test strips as they are less accurate and less user-friendly.

Water hardness is not as easy to measure in the field and requires submitting a sample to a laboratory. Sampling one time each year should be sufficient once you have determined a baseline.

If you are looking for more information on identifying or solving water quality problems, please contact your regional USGA agronomist. They can help interpret test results and provide guidance on ways to improve your pesticide performance. 

 

John Daniels is an agronomist in the Central Region.

 

Sources

Chahal G. S., D.L. Jordan, D. Burton, D. Danehower, A.C. York, P.M. Eure, and B. Clewis. 2012. Influence of water quality and coapplied agrochemicals on efficacy of glyphosate. Weed Tech. 26: 167-176.

Fidanza, M.A., B.B. Clarke, and P. Majumdar. 2009. Evaluation of fungicides and water carrier pH for dollar spot control in creeping bentgrass, 2007. Plant Disease Management Report. 3: T070.

Fukuto, TR. 1990. Mechanism of action of organophosphorus and carbamate insecticides. Environmental Health Perspectives. 87: 245-54.

Sarmah, A. K., R.S. Kookana, M.J. Duffy, A.M. Alston, and B.D. Harch. 2000. Hydrolysis of triasulfuron, metsulfuron-methyl and chlorsulfuron in alkaline soil and aqueous solutions. Pest Management Sci. 56: 463-471.

Stacy, T., and R. Latin. 2020. The influence of water pH on efficacy of fungicides for turf disease control. Applied Turfgrass Sci. 

 

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