Impact of demethylation inhibitor (DMI) fungicides on clipping yield and rooting depth of creeping bentgrass

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Demethylation inhibitor fungicides (DMIs) have been used to manage a wide range of turfgrass diseases for many decades. Unfortunately, this class of fungicide can have unwanted plant growth regulator (PGR) effects on amenity turfgrasses. Recently, a number of new DMI fungicides have been registered for turfgrasses and are seeing expanded use. To determine if differences exist in the PGR-related activity among products, a 2-year field study was conducted examining six different DMI fungicides. Fungicides were applied to creeping bentgrass maintained at 0.33 cm and applied five or six times every 14 days at equivalent active ingredient rates. The results demonstrated that although paclobutrazol statistically reduced clipping weights, there was very little effect from DMI fungicides. In the first study year, propiconazole did produce higher clipping weights on two rating dates but this was not observed in the second year. Rooting depth was unaffected by any of the chemicals in either year. Although phytotoxicity may be a concern of turfgrass managers when applying DMI fungicides during the summer, it seems unlikely that these materials applied without the additional use of labeled PGRs will have any noticeable negative effects on foliar and root growth of creeping bentgrass in New England.

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