Microbial-based control of diseases is a burgeoning area of interest in agricultural production, and the potential of such materials in turfgrass management is an intriguing idea. One biological control agent studied for use in turfgrass was Pseudomonas aureofaciens strain Tx-1, a commercial biocontrol material designed to be grown at the golf course and then injected through nighttime irrigation.
It has been shown that Tx-1 is effective at inhibiting growth of the pathogens that cause dollar spot (Sclerotinia homoeocarpa F.T. Bennett) and brown patch (Rhizoctonia solani Kuhn), but this work has largely been done in the laboratory or greenhouse. There wasn’t much work that studied the organism’s effectiveness in the field. So, the turfgrass gurus and microbiologists at Purdue University designed a study that evaluated the effectiveness of Tx-1 applied through fairway irrigation.
The study was conducted on Crenshaw creeping bentgrass and Astoria colonial bentgrass fairways to study the impact of the Tx-1, nitrogen (N) fertility and fungicides on dollar spot (creeping bentgrass) and brown patch (colonial bentgrass) activity. Every night (May-September in each year), a fresh batch of Tx-1 was grown, and it was then injected into the irrigation system for subsequent application to plots receiving that treatment.
The Tx-1 treatments were applied separately and in combination with the other treatments of N fertilizer (21.4 or 43.7 pounds N/acre [24 or 49 kilograms N/hectare], applied twice per year) and fungicide (none, preventive, curative and a second biological, Trichoderma harzianum). Preventive fungicide treatments were labeled rates of rotated chlorothalonil and propiconazole, while the curative treatment was labeled rates of chlorothalonil.
In addition to these two experiments, a third trial examined the efficacy of Tx-1 in extending fungicide effectiveness on dollar spot, with eight fungicides and two rates of Tx-1 evaluated. For all three studies, the collected data was disease severity, recorded as the number of dollar spots, and percent area of affected turf (for brown patch). This data was transformed into data called Area Under the Disease Progress Curve (AUDPC).
For brown patch, the application of Tx-1 never affected AUDPC and had little effectiveness on brown patch development in the field. Similarly, N rate had no effect on brown patch. Application of fungicides, both preventively and curatively, reduced brown patch.
For dollar spot, in the first year, application of Tx-1 reduced dollar spot 37% when compared with dollar spot infection in the untreated control plots. However, this reduction was not observed in the second year of the experiment, when application of Tx-1 had no effect on dollar spot. Application of the higher N rate reduced dollar spot, and application of fungicides (curative or preventive) reduced dollar spot by up to 94%. Combinations of Tx-1 and N fertilizer did not improve control, as compared with only N application.
In the third experiment, did the application of Tx-1 extend the effectiveness of fungicides for dollar spot control? Yes, to a small degree. The effectiveness of applied Tx-1 (and ability to extend fungicide effectiveness) only occurred in early June when dollar spot pressure was low. There were never any negative interactions between any of the fungicides and the applied Tx-1.
So, for dollar spot, field studies indicated some marginal ability of the biocontrol material Tx-1 to control dollar spot, but only when disease pressure was low. It also showed some benefits for extending the duration of fungicide disease control. Even though there were some slight benefits, the authors concluded that the practical issues of delivering this organism through golf course irrigation (dilution, uniformity, handling) produced a product with marginal practical value.
It should be noted that the commercial system to deliver this biocontrol is long gone from the commercial marketplace, and, as of this writing, there appears to be no research activity with this particular material. But this work clearly demonstrates the kinds of effort needed to appropriately test biocontrol materials and to identify future compounds that will work more effectively and efficiently and will benefit golf course superintendents.
Source: Hardebeck, G.A, R.F. Turco, R. Latin and Z.J. Reicher. 2004. Application of Pseudomonas aureofaciens Tx-1 through irrigation for control of dollar spot and brown patch on fairway-height turf. HortScience 39:1750-1853.
Editor’s note: Read all of Beth Guertal’s recent Verdure columns.
Beth Guertal, Ph.D., is the Rowe Professor of Soil Fertility in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and past president of the Crop Science Society of America. She is a 22-year member of GCSAA.