Influence of Spray Programs with Phosphite Fungicides on Turf Quality in a Mixed Creeping Bentgrass/Poa Annua Soil-Based Green, 2004.

CREEPING BENTGRASS (Agrostis palustris ‘Penncross’) ANNUAL BLUEGRASS (Poa annua)

Anthracnose; Colletotrichum graminicola

Brown patch; Rhizoctonia solani

Leptosphaerulina leaf blight ; Leptosphaerulina trifolii

Vincelli, E. Dixon, D. Williams*, and P. Burrus*

Dept. of Plant Pathology

*Dept. of Agronomy

University of Kentucky Lexington, KY 40546-0312

Influence of spray programs with phosphite fungicides on turf quality in a mixed creeping bentgrass/Poa annua soil-based green, 2004.

The test was conducted on a Maury silt loam located at the University of Kentucky Turf Center near Lexington. The turf was maintained at 0.188-in. mowing height and fertilized with 1.5 lb N/1000 sq ft as urea on Oct and Nov 03, and with 1.0 lb N/1000 sq ft as urea on Jun. The green was intentionally maintained as nitrogen deficient through the test period, in order to evaluate performance of fungicides under low fertility conditions. Plots m easured 4 ft x 4 ft with 2-ft borders, and were arranged in a randomized complete block design with three replications. Fungicide sprays were applied using a CO2-pressurized hand-held sprayer fitted with Spraying Systems 8003E flat-fan nozzles delivering 1.5 gal/1000 sq ft. Treatments were first applied on 20 May, and continued biweekly until 28 Jul. Visual estimates of turf quality were taken on several occasions and included deterioration of leaf color and density as well as developing leaf necrosis from several diseases, but excluded damage from dollar spot in the assessments (except 26 Jul). Selected treatments comparing phosphite-based spray programs were evaluated on more occasions than all other treatments in this trial, in order to compare these treatments as thoroughly as possible. These additional assessments are presented in this report. The level of infestation by Poa annua was visually estimated 11 May, when color differences between the two grass species and the presence of Poa annua seed heads facilitated discrimination. The percent of Poa annua per plot averaged 41.3 % and did not differ significantly between treatments. Data were analyzed using ANOVA and Waller-Duncan k-ratio ttest, (k=100, P=0.05).

Weather was moderately favorable for disease development. On 7 Jul approximately 50% of the diffuse turf damage in the trial was due to brown patch, 35% anthracnose, and 15% Leptosphaerulina leaf blight. Significant differences in turfgrass quality were apparent among spray programs with phosphite fungicides (Chipco Signature , Alude, Vital, and Resyst). No phytotoxicity or growth regulator effects were noted in the trial.

^z Scored on a 1-9 scale, where 9= excellent turf health. Dollar spot damage was excluded from turf quality assessments.

^y ratings taken by observer A (Paul Vincelli)

^x ratings taken by observer B (Ed Dixon)

^w Means within the same column followed by the same letter are not significantly different, Waller-Duncan k-ratio t-test (k=100, P=0.05).

^v One of the two tank-mixes was applied alternately every two weeks between 20 May and 28 Jul.

^u DAT= number of days after treatment the data were taken.

^z Scored on a 1-9 scale, where 9= excellent turf health. Dollar spot damage was excluded from turf quality assessments.

^y ratings taken by observer A (Paul Vincelli)

^x ratings taken by observer B (Ed Dixon)

^w Means within the same column followed by the same letter are not significantly different, Waller-Duncan k-ratio t-test (k=100, P=0.05).

^v One of the two tank-mixes was applied alternately every two weeks between 20 May and 28 Jul.

^u DAT= number of days after treatment the data were taken.

^z Scored on a 1-9 scale, where 9= excellent turf health.

^y ratings taken by observer A (Paul Vincelli), Dollar spot damage was excluded from turf quality assessments.

^x ratings taken by observer B (Ed Dixon) Dollar spot damage was excluded from turf quality assessments.

^w ratings taken by observer C (Paul Burrus), included DS in ratings.

^v Means within the same column followed by the same letter are not significantly different, Waller-Duncan k-ratio t-test (k=100, P=0.05).

^u One of the two tank-mixes was applied alternately at two week intervals between 20 May and 28 Jul.

^t INT=interval between sprays in weeks.

^s DAT= number of days after treatment the data were taken.