Dynamics of Foliage and Thatch Populations of Introduced Pseudomonas fluorescens and Streptomyces sp. on a Fairway Turf

Populations of bacteria (Pseudomonas fluorescens A506 and Streptomyces sp. strain 93) applied to a creeping bentgrass/annual bluegrass fairway turf were followed over time on leaves and thatch. While introduced populations remained at detectable levels over a period of 11–25 days, they usually declined gradually and did not increase after their application to turf. Streptomyces rapidly disappeared from leaves while P. fluorescens was able to maintain similar population sizes on both thatch and leaves, after an initial decline of about 1-log unit, showing that it was actively colonizing the foliage despite loss of biomass from lawn mowing. Throughout these experiments, populations of indigenous microbes on foliage and thatch remained stable, about 10⁶ and 10⁸ cfu g⁻¹ for fungi and bacteria, respectively, and were not affected by the application of bacterial antagonists. Niche-clearing with hydrogen peroxide, which temporarily reduced the population size of indigenous microorganisms two-fold, caused population size of P. fluorescens to increase approximately ten-fold within 24 h, while it declined by about one log unit on untreated turf. It is concluded that the indigenous microflora competes with introduced bacterial antagonists and interferes with their establishment and persistence on turf. Additional studies with P. fluorescens revealed that its population size was inoculum dose-dependent and that solid top dressing was slightly more efficient than spraying liquid suspension in establishing the antagonist. It was possible to maintain P. fluorescens populations above 10⁵ cfu/g of thatch and leaves for 2 weeks or more with both top-dressing or spraying with about 1 to 3 × 10¹⁰ cfu m⁻².