and sulphur-coated urea were evaluated from 1991 to 1993 on a creeping bentgrass (Agrostis palustris) green and a Kentucky bluegrass (Poa pratensis) lawn for their effects on soil bacterial and fungal populations and dollar spot disease incidence. Over the 3 yr, fertilizers were applied every 4 wk at recommended rates from early June to September, and once again in November. Application of Ringer fertilizers, ammonium nitrate and sulfur-coated urea gave rise to significantly higher microbial populations on turfgrass leaves and in thatch and soil than most other fertilizers. In most experiments, Ringer fertilizers also improved water retention in thatch compared to other treatments. Ringer Greens Super®, Ringer Turf Restore®, or ammonium nitrate on the creeping bentgrass green significantly suppressed dollar spot disease compared to the other amendments or the untreated control, but for most of the season, they did not control disease as well as the fungicide chlorothalonil. Nitrate leaching from inorganic nitrogen fertilizers has the potential to be a significant source of nitrate contamination of ground water in urban areas where turfgrass is the major living ground cover (17). Frequent application of inorganic fertilizers such as ammonium nitrate can change the soil pH and consequently may alter soil microbial populations and affect plant growth (19, 20, 22). Concerns regarding environmental quality are prompting the development and use of various kinds of organic amendments or fertilizers to reduce or replace inorganic fertilizer and synthetic pesticide use. Organic amendments have been reported to suppress soilborne plant pathogens (6, 15). Recently developed organic turf amendments, such as Ringer Lawn Restore®, Ringer Greens Super® and Ringer Turf Restore® are derived from hydrolysed poultry feather meal, blood meal, wheat germ, potassium sulfate and bone meal. These products contain microorganisms that may be very important in the biological control of diseases caused by species of Phytophthora, Pythium, Rhizoctonia, and Sclerotium (18). They may also directly or indirectly affect the decomposition of thatch and nutrient transformations in soil. Turfgrass thatch is a complex of dead and living roots, stems and organic debris (2). Excessive thatch accumulation can be detrimental to turf quality and is normally controlled through verticutting and top-dressing (2). High microbial activity is important to thatch decomposition and nutrient recycling in turf (3). Cole and Turgeon (5) reported that 1 g of dry soil or thatch from turf of Kentucky bluegrass (Poa pratensis L.) can contain up to 2.8 x 10 8 bacteria and up to 2.8 x 10 6 fungi. Berndt et al. (3) found that application of a range of organic amendments reduced thatch thickness of Kentucky bluegrass, whereas Mancino et al. (11) found that addition of organic amendments increased thatch thickness and soil fungal counts. Soil bacteria and fungi can increase the availability of plant nutrients in soil, form symbiotic associations with turfgrass roots, produc...

The effectiveness of thatch control practices commonly employed in Ontario on Penncross creeping bentgrass turf maintained as a putting green was evaluated from July 1976 to October 1979. The most effective treatments were coring and vertical mowing followed by topdressing, and topdressing alone. The least amount of winter injury occurred in plots where coring was followed by topdressing. Coring reduced thatch accumulation more than did vertical mowing. Vertical mowing increased winter injury and annual bluegrass content in the plots more than did coring. Thatch accumulation was less at the 5-mm than at the 8-mm mowing height. Nitrogen treatments of 2 and 4 kg N. 100 m-2 did not influence thatch accumulation.

Under pot culture and field conditions, ethephon at rates up to 8 kg ha-t was more injurious to annual bluegrass than to Penncross creeping bentgrass. Ethephon significantly decreased the quality, spreading ability and shoot weight of annual bluegrass, whereas sward quality of the creeping bentgrass grown in pot culture was increased, spreading ability was unaffected and shoot dry weight decreased. Increasing the number of applications at all concentrations increased injury to annual bluegrass and a single application at I kg ha ' reduced annual bluegrass seedhead production. Mots cl6s: Poa annua, Agrostis palustris,6th6phon, qualit6 du gazon

KoHr-vEtn, G. P. eNo EcceNs, J. L. 1983

Hollow tine core cultivation is practiced for the management of creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.) Farw.; syn. A. palustris Huds.] golf course greens and fairways to increase water infiltration, increase turf root and shoot growth, and control thatch. Benomyl [methyl 1‐butylcarbamoyl)‐2‐benzimidazole carbamate] is commonly used on turf as a soil drench for the control of disease such as dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett). Our objective was to determine the effect of core cultivation on the movement of a systemic pesticide in thatch and soil and the uptake by turfgrass using benomyl as a model. Core cultivation was conducted 1, 7, and 14 d before benomyl application in a field trial during 1992 and 1993 to study the effect of coring and time of coring on the movement and uptake of benomyl and control of dollar spot disease. Fungicide levels in turfgrass clippings, thatch and soil were determined by bioassay. Core cultivation 1 d before benomyl treatment provided the longest lasting uptake of benomyl and control of dollar spot disease compared with 7 and 14 d before benomyl treatment. Clipping, thatch, and soil samples from areas close to the coring holes had significantly higher (P = 0.05) levels of fungicide residues than those farther from the coring holes. This study suggests that core cultivation shortly before benomyl application can increase movement of benomyl into thatch and soil, thereby increasing uptake of benomyl by turfgrass and improving disease control.