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Putting the pH in pH-ungicide mixology

By and |  January 8, 2018 0 Comments

Four runs of the experiment were conducted in field plots on creeping bentgrass maintained at greens height.

Fungicides are mixed with water and applied as a dilute spray to control diseases on golf course turf. Although published reports show that water quality can influence the performance of certain herbicides, evidence of similar effects on fungicide efficacy is weak and largely anecdotal.

The objective of this research was to investigate the influence of water pH on the efficacy of fungicides commonly used against dollar spot (Sclerotinia homoeocarpa), a problematic disease of creeping bentgrass (Agrostis stolonifera L.) We considered three fungicides (metconazole, thiophanate-methyl and iprodione) mixed with water stabilized at three pH levels (pH = 5.0, 7.0 and 9.0) in in vitro and field experiments. We also considered a time factor, i.e., the time between mixing and application, where time = 0 indicated that fungicides were applied immediately after mixing, and time = 24 indicated that fungicides were applied 24 hours after mixing.

Results from field experiments revealed no difference in fungicide performance when mixed in acidic (pH = 5.0), neutral (pH = 7.0) and alkaline (pH = 9.0) water. In addition, the time factor revealed little or no difference for all fungicides and water pH levels.

Results from in vitro work supported field observations — we observed few differences in pathogen growth for pH and time factors. Therefore, water pH is not likely to influence performance of these three fungicides, even when time between mixing and application is 24 hours.

Although tank mixing products to neutralize water pH may be important for other reasons, such as compatibility with other tank-mixing products, results reported here support that water pH does not influence fungicide efficacy for control of dollar spot on creeping bentgrass.

Trevor Stacy and Rick Latin, Ph.D., Purdue University. You may reach Trevor Stacy at for more information.

Photo: Trevor Stacy

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