Verdure: Spray water pH is all good

Purdue University Researchers examined the effects of water-carrier pH on fungicide performance.


Filed to: Fungicides

spraying fungicide

The concept of pH was first described and introduced by S.P.L. Sørensen in 1909. He was a chemist at the famous Carlsberg Laboratory in Copenhagen, Denmark, which focused on biochemical research to improve the brewing of beer. So perhaps we owe the discovery and use of pH to beer?

You may remember from chemistry class that pH refers to the acidity or alkalinity of an aqueous solution. The pH scale is 0 to 14, where < 7 is acidic, 7 is neutral, and > 7 is alkaline. The pH scale is logarithmic and inversely indicates the amount of hydrogen ions in solution, but that 0-to-14 scale makes it easier to use and interpret. For example, in pure water, the hydrogen ion concentration is 10-7 gram equivalents per liter, which reads as a pH of 7 on a pH meter. Of note, pH historically refers to the “potential of hydrogen” or the “power of hydrogen.”

When adding certain pesticides into a spray tank, the wrong pH of that water can cause those pesticides to break down and become ineffective. For example, organophosphorus and carbamate insecticides added to high-pH water carriers can result in alkaline hydrolysis, a chemical reaction that accelerates chemical decomposition. Similar examples occur with certain agricultural herbicides in very acidic or very alkaline spray water.

What about spray water pH and fungicides for turfgrass disease control?

Researchers at Purdue University (West Lafayette, Ind.) examined the effects of water-carrier pH on fungicide performance for dollar spot (Clarireedia spp.) control. Field experiments were conducted in the standard turfgrass test plot procedure with treatment randomization and replication. Three liquid fungicides — iprodione (FRAC = 2), metconazole (FRAC = 3) and thiophanate-methyl (FRAC = 1) — were applied at recommended label rates for dollar spot in a creeping bentgrass (Agrostis stolonifera L.) sand-based putting green. Mowing height was 0.135 inches (3.429 millimeters).

Each fungicide was added to water with a pH of 5.0, 7.0 and 9.0 (i.e., three fungicides each at three pH levels, for nine treatments total). The pH was adjusted by adding hydrochloric acid (to make it acidic) or sodium hydroxide (to make it alkaline) to deionized water (neutral pH). Buffering agents kept the pH stable. All treatments were applied immediately after mixing, and a second set of treatments was mixed and remained in the spray bottles then applied 24 hours later. All treatments were applied in 1.75 gallons water carrier per 1,000 square feet (713 liters per hectare) once then monitored for dollar spot control.

These field experiments were conducted twice during the summer of 2016 and repeated two more times during the summer of 2017. Combining the results from all four field experiments and with all three fungicides, water-carrier pH did not affect their ability to control dollar spot, and neither did waiting 24 hours before making the applications.

Laboratory experiments were conducted with the same three fungicides. In petri plates, various concentrations of the fungicides (i.e., 0, 0.01, 0.1, 1.0 and 10 ppm active ingredient) were amended into potato dextrose agar media. Those fungicides were made in stock solutions at those same three pH levels (5, 7 and 9). In the center of the plate was placed an isolate of the dollar spot pathogen, and its growth was measured over three days. Again, all three fungicides effectively suppressed the pathogen’s growth regardless of pH level.

Therefore, both field and laboratory experiments showed no differences in fungicide efficacy (i.e., ability to control dollar spot) from all three fungicides evaluated when mixed in spray water of pH 5 (acidic), 7 (neutral) or 9 (alkaline). Today, both liquid and dry pesticide products are formulated with various adjuvants, stabilizers, inerts and other technology to ensure the active ingredient(s) maintain their chemical integrity and perform as intended. But just to be on the safe side, make sure the water-carrier pH is near neutral (pH = 7) — and use a buffering agent if needed — before adding pesticides into that spray water. It is also a good idea to have the spray water tested by a reputable laboratory.

Incidentally, Momma Fidanza always says that water is the most important ingredient when making pasta.

Source:  Stacy, T., and R. Latin. 2020. The influence of water pH on efficacy of fungicides for turf disease control. Crop, Forage & Turfgrass Management 6:e20007 (

Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 21-year member of GCSAA.