Systemic fungicides applied to Kentucky bluegrass (Poa pratensis L.) turf often cause visible alterations in plant morphology. Compounds derived from 5‐pyrimidinemethanol and 1,2,4‐triazole may induce changes in color, growth rate, and density of the stand while also providing outstanding disease control. Because plant growth and stress responses contribute to the severity of many turfgrass diseases, nontarget plant growth regulating effects could influence the disease control activity of systemic fungicides. Studies were conducted to determine the effects of several systemic fungicides on Kentucky bluegrass morphology and physiology. Fungicides were compared, when possible, to growth‐regulating compounds with similar chemical and/or biological properties. Commercially available or experimental formulations were applied as soil drenches to greenhouse‐grown seedlings and as foliar sprays to field‐grown sod of ‘Merion’ and ‘Fylking’ Kentucky bluegrass. Application rates of the fungicides were as recommended for controlling Fusarium blight. Growth regulators were applied at rates comparable to the fungicides or at rates previously reported to have an effect on plant growth. Oven‐dry root weights, shoot densities (tillers plus nonemerged rhizomes), and leaf growth rates were measured. The chlorophyll content of young leaves was determined by extraction with dimethylsulfoxide. Chlorophyll retention of excised, mature leaves was measured following dark incubation. Total nonstructural carbohydrate (TNC) content in mature foliage was determined using the anthrone method. When applied to greenhouse‐grown seedlings, pyrimidinemethanol and triazole derivative fungicides reduced leaf growth rates, shoot densities, and root weights of one or both cultivars. Pyrimidinemethanols increased the chlorophyll content of Fylking and increased TNC contents of both cultivars. Triazoles also increased TNC levels while increasing chlorophyll retention of excised leaves. Chlorophyll retention was also enhanced by cytokinin analogs, including a benzimidazole fungicide. Results obtained from field experiments were inconsistent although similar growth‐regulating effects were observed following certain treatments. Our results show that the systemic fungicides studied have nontarget plant growth‐regulating activity on Kentucky bluegrass. These effects could influence the severity of stress related diseases such as Fusarium blight.

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Development of improved management strategies for controlling thatch on tuifgrasses is limited by an incomplete understanding of thatch biology. Mechanisms whereby fungicides cause thatch to accumulate in turfgrass were investigated, by evaluating the influences of fungicides on rates of tissue production and thatch decomposition. Fourteen fungicides, one nematicide, and five mixed‐fungicide programs were applied repeatedly (up to nine times annually), over a 4‐yr period, to a field‐grown Kentucky bluegrass (Poa pratensisL.) turf on a soil of the fine, illitic mesic family of Glossoboric Hapludalfs. Measurements were made of thatch depths, root and leaf clipping weights, shear strength of sod, and decomposition rates for thatch implanted into the turfs. Compounds that caused thatch to become deeper (p= 0.05) than in the nontreated control included benomyl, cadmium succinate, fenamiphos, iprodione, and mancozeb. Treatments in which these pesticides were used were characterized by sod shear strengths greater (p= 0.05) than in the control. Thatch accumulations were related mostly to the amounts of roots in the surface 4 cm. None of the studied fungicides significantly (p= 0.10) reduced the apparent rate of thatch decomposition. Fungicides in this study therefore appeared to induce thatchiness in Kentucky bluegrass by increasing the rates of root and rhizome production and not by reducing the rate of litter decomposition.

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Each year from 1991 to 1999, a disease matching the description of gray leaf spot (1) was observed in the central and north central regions of Illinois. Disease severity was low (<10% blight) from 1991 to 1994 and 1999 and was severe (>50% blight in some areas) from 1995 to 1998. The disease was observed on Lolium perenne (perennial ryegrass) golf course fairways and sports fields. Isolations of Pyricularia grisea were made from L. perenne collected from golf courses in Bloomington, Decatur, Kankakee, Pekin, Urbana, and Moline, IL. All isolates were collected from surface-sterilized, symptomatic leaves. Cultures were maintained on one-fifth strength potato-dextrose agar (PDA) and induced to sporulate on full-strength oatmeal agar. All isolates in culture displayed vegetative and conidial characteristics similar to those previously described for P. grisea (1). Twenty-five different L. perenne germ plasms were inoculated with isolate WF9826 (Kankakee) using a suspension of 1 × 105 conidia per milliliter. The 4-week-old lawns (100 plants per 3-cm-diameter cone-tainer) of each ryegrass germ plasm were inoculated by spraying foliage with the conidial suspension until runoff. Inoculated and uninoculated lawns were enclosed in plastic bags and placed in an incubator (16 h light; 28°C) for 7 days. Disease severity was rated using a scale of 0 to 10 (10 = 100% blight). Each treatment was replicated three times, and all experiments were repeated four times. Small blue-gray, water-soaked lesions with dark brown borders were observed on leaves of all inoculated ryegrass germ plasms. Advanced symptoms included blighting of much of the leaves. The mean disease severity rating was 3.8 (range 2 to 7) for all experimental units and all 25 germ plasms. P. grisea was isolated from leaves that were inoculated with WF9826. This is the first report of gray leaf spot of perennial ryegrass caused by P. grisea in Illinois. Reference: (1) P. J. Landschoot et al. Plant Dis. 76:1280, 1992.