The Influence of Carrier Water pH on Efficacy of Fungicides for Turf Disease Control.

Fungicides are most often mixed with water and applied as a dilute spray for controlling 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 efficacy of fungicides commonly used against dollar spot, a problematic disease on creeping bentgrass. 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 fungicides were applied immediately after mixing, and time =24 indicated that fungicides were applied 24 hours after mixing.   Results from field experiments revealed little or no difference in fungicide performance when mixed in acidic (pH=5.0), neutral (pH=7.0), and alkaline (pH=9.0) water. Also, the time factor was not significant for all fungicides and water pH levels.  Results from in vitro work supported field observations—few differences in pathogen growth were observed for pH and time factors.  Although tank mixing products to neutralize water pH may be important for other reasons, results reported here support the null hypothesis that water pH does not influence fungicide efficacy for control of dollar spot on creeping bentgrass.