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9 Ways Top Growers Manage pH to Save Money How managing spray tank pH optimizes greenhouse chemical performance

Like most growers, you probably understand the effects of pH on your growing media and how key it is to a plant’s ability to thrive. Likewise, you’re probably well versed in the methods and measures you can take to monitor and adjust pH in these situations, according to your growing needs.

But how well do you understand the effect of pH on those expensive greenhouse chemicals you apply? This is an area that often goes overlooked. In fact, many growers mistakenly attribute problems such as phytotoxicity or poor pesticide performance to an incorrect rate of application, pesticide resistance, or even the chemical itself, when in fact the real culprit may be improper pH of the water in your spray tank.

The pH of the water in your spray tank matters
The fact is, the pH of the water in your spray tank significantly affects the effectiveness of many greenhouse chemicals. Not optimizing for pH when using them is effectively pouring money down the drain—a lot of money.

Here’s why. As a rule, most fungicides, bactericides, insecticides, and herbicides have specific, targeted pH ranges that optimize their performance. Always read the label to find each product’s specific pH recommendation (it would also be a good idea to check its compatibility for tank mixing purposes at this time). You’ll find that most pesticides work best in slightly acidic solutions, but water used for spraying is usually alkaline.

The result? Failing to appropriately adjust the spray tank pH can dramatically shorten the half-life and effectiveness of many products, increase the likelihood of phytotoxicity, or simply waste valuable chemicals that aren’t being deployed at their full potential. None of these outcomes is satisfactory.

Here are nine things you can do to manage pH to get the most bang for your buck out of your greenhouse chemicals.

  1. Don’t just assume—know the pH of your source water
    Top growers check their source water pH frequently. Water quality can vary greatly and is affected by a number of factors, including geography, season, and water source. For example, rainwater and surface water tend to contain low levels of minerals, whereas water found in deep aquifers in coastal southeastern areas can contain relatively high levels of minerals. Mineral concentration in wells tends to increase in dry seasons and drop in rainy seasons, and surface water ponds will often contain organic compounds. These situations can create challenges for growers, and chemical performance can be adversely affected as a result. Knowing the water quality before mixing it with chemicals is crucial to growing healthy plants and to optimizing pesticide performance.1
  2. Collect and test a water sample to find its pH before mixing
    Use a clean glass jar or bottle (or other non-reactive container) to collect a water sample, but do so only after allowing the water to run a few minutes; you want to make sure any standing water has been flushed from the hose and pipes so that the water you’re testing matches the water you’ll be using in your spray solution. Find the water’s pH by using pH test strips or a pH meter immediately after collecting the sample.2
  3. Adjust the pH of spray tank water with buffers or water conditioning agents that are safe for you and your staff to use.
    There are many adjustment compounds on the market designed to modify spray solution pH to its desired range. It’s very important to get the water pH right before adding any chemicals. Check the pH after adding each chemical because each subsequent pesticide can alter the pH of the tank mix.
  4. Double-check the recommended application rate of the product you’re spraying against the setting on your sprayer.
    This is the growers’ version of the carpenter’s axiom, “measure twice, cut once”. You want to make absolutely sure you’ve got everything adjusted correctly before you begin spraying. For this reason, it’s a good practice to rinse the tank and sprayer before mixing, even if you believe it’s clean. It’s possible someone used it before you and either got busy and forgot to clean it, or simply didn’t clean it well. Mom was right, better safe than sorry.
  5. Always recheck the pH after you add the chemical to the tank to make sure you’re in the product’s “sweet spot,” and tank mix with care.
    Greenhouse chemicals have their own pH and can raise or lower the tank mix pH. Readjust the final solution pH to ensure that you are in the product’s sweet spot. Taking this added precaution will help ensure that the tank mix pH stays in a desirable range. And remember, not all pesticides are compatible, so tank mix with care, always carefully checking manufacturer labels. When in doubt, stop tank mixing and consider rotational sprays as an alternative. It’s very easy to make a mistake and unwittingly destroy hundreds of dollars’ worth of valuable chemicals.
  6. Always spray promptly after mixing chemicals.
    It might be a familiar scenario: you mix up your tank chemicals and then get interrupted or sidetracked by another project before getting a chance to spray. While it can and does happen, it’s never advisable to allow a solution to stand idle for several hours or overnight before spraying. Settling may occur, and pesticide performance will diminish over time. Make it a priority to mix, spray, and clean up as promptly as possible. You will be rewarded with optimal performance of your chemical sprays.3 (Note that even if you allowed your solution to sit for several hours, it’s still best to spray it to help prevent disposal and run-off issues.)
  7. Monitor the temperature of your spray tank.
    Heat kills, it’s as simple as that. A temperature increase of just 18° F doubles the rate of pesticide decomposition. A hot sun beating down on your spray tank will facilitate hydrolysis, and agitating the spray tank will further increase the solution’s temperature.4  An ideal spray tank temperature should fall between 70°F and 80°F.
  8. Invest in a good pH meter and keep it and your adjustment compounds up-to-date.
    Many models of pH meters are available. Be sure to select one that is accurate within +/- 0.2, has a resolution of 0.1 pH units, a pH range of 2 to 12, and has 2-point calibration capabilities when using a buffer solution of pH 4 and pH 7. Less expensive pH meters tend to be less accurate and will require frequent replacement. Since pH management is crucial to the performance of your chemicals, invest in a good quality pH meter. Buy calibration solutions of pH 4 and pH 7 and make sure to use them prior to their expiration dates.
  9. Refer to the product label of each manufacturer.
    Perhaps not as gripping as a Stephen King novel, but these threats are real. Always read and follow the directions on product labels.

Following these steps will help you get the most out of your greenhouse chemical applications and the money, time and effort you put into using them. Again, always follow the directions on the manufacturer label and make any pH adjustments needed. A pH that does not fall within the recommended range can reduce pesticide efficacy and cost you time, money and frustration, while increasing the risk of crop damage and loss. Take control of pH and know you’re getting the most out of your chemical applications.

 


  1. Bodie V. Pennisi, and Paul A. Thomas, “Essential pH Management in Greenhouse Crops: Part I. pH and Plant Nutrition,” The University of Georgia, Cooperative Extension, College of Agricultural & Environmental Sciences, http://www.caes.uga.edu/Publications/pubDetail.cfm?pk_id=7351&pg=np&ct=essential%20ph%20management&kt=&kid=&pid=&lid=17696.
  2. Tina Smith, “Effects of pH on Pesticides and Growth Regulators,” University of Massachusetts Amherst, The College of Natural Sciences, Agriculture & Landscape Program, Greenhouse Crops and Floriculture Program, http://extension.umass.edu/floriculture/fact-sheets/effects-ph-pesticides-and-growth-regulators
  3. Mark Halcomb, “The pH of the Spray Water is Very Important,” The University of Tennessee Extension, http://www.utextension.utk.edu/mtnpi/handouts/General/pH_of_Spray_Water.pdf.
  4. Ibid.

 

 

 

 

 

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