Disease Enhancement and Kentucky Bluegrass Quality As Influenced By Fungicides

Abstract

AbstractDeleterious non‐target fungicide effects in turf need better documentation, while beneficial effects should be exploited. The main objectives of this field study were to identify turfgrass quality and non‐target disease enhancement effects of five fungicides applied to four Kentucky bluegrass (Poa pratensis L.) cultivars. Fungicides were applied monthly from April through September between 1983 and 1987 to turf grown on a Chillum silt loam (fine silty, mixed mesic Typic Hapludult). Quality of Kentucky bluegrasses (KBG) was improved significantly when fungicides controlled injurious diseases. Most notably, triadimefon [l‐(4‐chlorophenoxy)‐3,3‐dimethyl‐ l‐(lH‐1,2,4‐triazol‐l‐yl)‐2‐butanone] improved quality by providing therapeutic activity against stripe smut [Ustilago striiformis (West.) Niessl.] in ‘Merion’; and summer patch (Magnaporthe poae Landschoot and Jackson) in Merion and ‘Sydsport’ KBG. Chlorothalonil (tetrachloroisophthalonitrile) and thiram (bis[dimethyl‐thiocarbamoyl]disulfide) were associated with a significant increase in stripe smut in Merion, and chlorothalonil increased summer patch in Merion, Sydsport, and ‘Vantage’. Triadimefon and benomyl ([methyl l‐(butylcarbamoyl)‐2‐benzimidazoIe carbamate]) increased leaf spot [Drechslera poae (Baudys.) Shoem.] in ‘South Dakota‘ KBG. Iprodione [3‐(3,5‐dichlorophenyl>‐^V‐(l‐methylethyl)2,'Mioxo‐limidazolidinecarboxamide] did not exacerbate any disease, provided long residual leaf spot control, and elicited a color enhancement. Except for leaf spot in South Dakota, these non‐target increases in disease by fungicides did not recur annually in each cultivar.