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Evaluation of Treatments for Control of Dollar Spot and Brown Patch of Creeping Bentgrass

Richard Latin

Objective

The objective of this research was to evaluate the performance of several fungicides and a biological control against dollar spot and brown patch on creeping bentgrass.

Rationale

Dollar spot and brown patch threaten the appearance and playability of bentgrass putting greens each year. Most fungicides applied to greens during a given season are aimed at limiting the damage sustained by both of these diseases. Concerns over the economics and negative public perception associated with fungicides have increased interest in biological disease control products. Currently, information on the performance of biologicals is largely testimonial. This research was initiated to generate performance data necessary for objective comparisons among disease control products.

How It Was Done

Turf on the experimental site was maintained at a height of approximately 6 cm and received conventional golf course care. Treatments were applied to 1m x 2m plots arranged in a randomized complete block design with 4 replications. Fungicides were applied with a CO₂ powered boom sprayer that delivered 2 gal per 1000 sq ft through three Tee-Jet 8004 flat fan nozzles. The biological treatment (BioTrek 22G) was a granular formulation and was evenly distributed over the plot surface by hand. Dollar spot epidemics developed from natural inoculum. Brown patch development was fostered by inoculation with millet seed infested with the brown patch pathogen on 26 June 1997. Treatments were applied at 14:21 on 28-day intervals, or according to the Mills-Rothwell model. The Mills-Rothwell model advises fungicide treatments when the maximum temperature is greater than 77F and relative humidity is greater than 90% for 3 out of any 7 day period. All treatments were applied initially on 4 June 1997. Dollar spot initially became apparent during the last week of June. Brown patch out breaks occurred during the last week of July. Plots were evaluated for disease periodically throughout the summer. Dollar spots were counted in each plot. Brown patch development was assessed by visual estimates of the percentage of plot that expressed brown patch symptoms.

Results

• Dollar spot and brown patch evaluation results are presented in Tables 12 and 13, respectively. Unsprayed plots showed a steady increase from a few spots on July 2 to 140 spots on August 13. Differences among treatments were readily apparent on July 24. Brown patch did not develop until early August. Similar to the results with dollar spot control, fungicides performed well, and the biological did not differ from the unsprayed plots.

• In general, the fungicide treatments provided acceptable control of dollar spot; the BioTrek treatments performed well only when used with a fungicide. It is possible that any nutritional value of the biological contributed to increased vigor of the turf, and enhanced conditions for brown patch development.

These results represent data from only 1 season. Valid conclusions will be drawn after 2 or 3 years of similar experiments. It appears that biological control applications are influenced to a greater extent by physical and bilogical elements of the environment, while fungicides perform consistently over a variety of environmental conditions. The concept and potential benefit of biological control warrant further experimentation, especially with regard to the timing of the product applications. Further testing will be conducted in 1998.

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