Have received several questions from golf course superintendents over the last few days about potential phytotoxicity from the use of Daconil Action (cholorthalonil + acibenzolar) on golf course greens and fairways. I have worked with Daconil Action for 7-8 years and have not seen any “unique” phytotoxicity associated with that product compared to chlorothalonil itself.
Having said that, we have seen phytotoxicity (thinning and bleaching of foliage with chlorothalonil products in general) at very close spacings and high rates on greens height annual bluegrass when applied during the summer. We ran an experiment last year and were trying to keep anthracnose out without using a penetrant fungicide that might affect turf physiology. We noticed phytotoxicity after 8 weekly applications of Daconil Ultrex 82.5WDG @ 5 OZ/1,000 SQ FT. This is way off the label rate, so it did not surprise me to see toxicity during hot weather. However, I have not seen phytotoxicity with Daconil Ultrex, Daconil Action, or any other product containing chlorothalonil at labeled rates or recommended intervals, especially if these products are alternated with other chemistries as we recommend.
The take home message is that turf mangers should keep the rates of any fungicides within label specifications, take mix and alternate chemistries to improve disease control, reduce the possibility of resistance and to prevent phytoxicity. Finally, avoid spraying any fungicide during the heat of the day.