A version of this article appears in GreenMaster Oct/Nov 2000
 

Biological control of turfgrass snow molds with the fungus Typhula phacorrhiza

Dr. Tom Hsiang, Dept. Environmental Biology, University of Guelph
Summary

For the past six years, we have been working on a biological control system for turfgrass snow mold diseases. We started out in 1994 looking for better strains of a fungus that could suppress gray snow mold disease caused by the fungi Typhula ishikariensis and Typhula incarnata. Dr. Lee Burpee, formerly at Guelph, and Dr. Naoyuki Matsumoto in Japan had found that some strains of a fungus named Typhula phacorrhiza could inhibit gray snow mold disease. We collected strains of T. phacorrhiza from corn fields all over southern Ontario. By 1997, we had identified five strains out of several hundred that work as well at suppressing gray snow mold as conventional fungicides. This work during the first three years was supported by the Canadian Turfgrass Research Foundation with matching funds from the Ontario Ministry of Education.

In 1998, we started on a new phase of this research with funding from the Canadian Turfgrass Research Foundation. This money was matched by Nu-Gro Corporation who are interested in commercialization of this product. Then funding from both organizations was matched by a federal program, the Natural Sciences and Engineering Research Council of Canada. As a result of the increased funding, we were able to expand the study to sites across Canada and begin more intensive work on biological processes involved in suppression. Although T. phacorrhiza can be found in abundance in corn fields after spring snow melt, the large majority of these isolates have little or no effect against gray snow mold. Since 1998, we have also tested and observed suppression of pink snow mold by T. phacorrhiza. Our continuing work is to develop ways of growing and formulating the inoculum of a select isolate of T. phacorrhiza (TP94671) that is antagonistic to both gray snow mold and pink snow mold, and well as studying the biology of the interactions. We are hoping for a registered product within two years formulated as a granular that can be applied with conventional turf management equipment.
 

Snow molds

The disease gray snow mold is caused by two species of fungi known as Typhula ishikariensis (with tiny dark black sclerotia) and Typhula incarnata (with small red sclerotia). The disease pink snow mold is caused by the fungus Microdochium nivale. These diseases can be found on grasses and cereals and are common in areas with heavy and persistent snow cover. For a review of the biology and management of of snow mold diseases, see Plant Disease 83:788-798, 1999, . In Canada, these diseases are commonly controlled with fungicides containing mercury, quintozene or thiram.  The costs of applying these synthetic fungicides coupled with environmental concerns led us to investigate alternative management approaches.
 

Typhula phacorrhiza

The fungus Typhula phacorrhiza is a close relative of the organisms which cause gray snow mold. It is known as a saprophyte which is a type of organism that lives on dead organic matter. It can be found all over the world in regions which typically have abundant organic matter (such as forest litter) and at least a few weeks of snow cover or near-freezing temperatures. In Canada, this species has been found most commonly associated with corn stalk residue after snow melt. It is a psychrophile which means that it likes cold temperatures. Under laboratory conditions, the fastest growth rate for this organism can be found near 15C. In many ways it is similar to the gray snow mold fungi, but it is not known to cause disease of turfgrasses although it has been found to be associated with dead patches of grass after winter snow melt.
 

Experimental Results

In the first years of research, we collected several hundred isolates of Typhula phacorrhiza and tested them in the lab for growth rate and production of resistant structures known as sclerotia. It is the sclerotia that allows this organism (and other organisms with sclerotia) to survive unfavorable conditions. After winter field testing of some of these isolates, we found that they have a large variation in their ability to suppress gray snow mold. However, the most active Typhula phacorrhiza isolates are suppressive to gray snow mold caused by either Typhula ishikariensis or Typhula incarnata in replicated and inoculated field trials. These results were consistent in three years of field tests (Canadian Journal of Botany 76:1276-1281, 1998).

We also examined the residual efficacy of the best Typhula phacorrhiza isolates, and found, after 5 years of field testing, that a single application of Typhula phacorrhiza in the first year can suppress gray snow mold disease for the next three years to an aesthetically acceptable level (Canadian Journal of Plant Pathology 21:382-387, 1999). In the fourth and fifth years, although suppression was still evident in some plots, the level of suppression was not aesthetically acceptable and less than that of a fungicide check treatment.

We also tested the fungicide sensitivity of select Typhula phacorrhiza isolates. We found that the mycelium (fungal strands) is sensitive to all the snow mold fungicides; but Typhula phacorrhiza mycelium is less sensitive to the fungicide Arrest® (thiram/carbathiin/carboxin) than Typhula incarnata and and less sensitive to Tersan® (benomyl) than the pink snow mold fungus. What this means is that an integrated disease management program could be developed that incorporates both the the use of conventional synthetic fungicides such as Arrest® and Tersan® along with Typhula phacorrhiza.

After the winter of 1999, we observed strong suppression of naturally occurring pink snow mold by Typhula phacorrhiza in trials near Barrie, Ontario. Although we had previously observed the suppression of pink snow mold by Typhula phacorrhiza in trials at the Guelph Turfgrass Institute, we had not specifically tested for this effect since the main target in earlier research was gray snow mold. In 1999,we set out to test the effect of Typhula phacorrhiza on pink snow mold in replicated tests across the country. Unfortunately for snow mold fungi and for snow mold researchers, the duration of snow cover across most parts of this country has been less in winters during the past few years, so we were unable to obtain sufficient snow mold disease in most locations for a proper test of suppression. However, we did have excellent results high up at a Golf Course in the Rocky Mountains (Figure 1). We had asked the staff to leave a 30 m by 30 m sward of creeping bentgrass fairway untreated in the fall of 1999 in order to test snow mold control. In the back part of the test area (Figure 1) were fungicide trials with existing and new fungicides. The best suppression of snow mold by any fungicide in this test was less than 85% while some treatments showed little to no suppression of the the heavy disease caused by both pink and gray snow molds in this area. In the front part of the test area, we had a small separate trial with Typhula phacorrhiza and three other treatments (Figure 1). Only the four 1m x 1m squares of green are visible and these had been treated with Typhula phacorrhiza the previous fall. A close-up shows the contrast between plots treated with Typhula phacorrhiza and those without (Figure 2). On plots treated with Typhula phacorrhiza, disease suppression was higher than 95%. This demonstrated the Typhula phacorrhiza could provide protection against very heavy disease pressure caused by both gray and pink snow molds.

Since 1999, we have also been working on a registration package for Typhula phacorrhiza. In order for a pest control product to be sold in Canada, it must be approved by the Pest Management Regulatory Agency (PMRA) which is part of Health Canada. The PMRA requires the following information in order to review whether a product should receive registration in Canada: 1) product characterization; 2) human and animal toxicology of product; 3) environmental toxicology of product; and 4) efficacy of product.

As for product characterization, we have conducted molecular DNA tests (Mycological Research 104:16-22, 2000) and measured growth rates and growth conditions of select isolates (Canadian J. Botany 77:312-317 , 1999). We are able to distinguish our best isolates from other closely related isolates and this allows us to track the fate and dispersal of this organism.

The toxicology of this organism (that is, whether it causes problems for humans and animals) has not been studied in any detail. There are no reports of this organism or any closely related organisms causing harm to humans or animals. The requirement for full toxicological examination of biological control agents may be the major obstacle to their implementation since the costs are prohibitive.

We have abundant details on the efficacy of this product and this year will be expanding our research to sites across the full breadth of this country (Figure 3). Currently we are concentrating our research on the biology of Typhula phacorrhiza as well as ways to produce it in large quantities. We are hoping for a product within 2 years formulated as a granular that can be applied with conventional turf management equipment.
 

Figure legends
 

Figure 1: Snow mold trials at a golf course in the Canadian Rocky Mountains photographed on 27 April, 2000. The plots in the top half (background) are snow mold fungicide trials. The plots at the bottom half (foreground) are Typhula phacorrhiza trials composed of four treatments with four replications. The four green 1m x 1m plots in the foreground were treated with T. phacorrhiza on 23 October 1999.
 

Figure 2: Close-up of plots of the Typhula phacorrhiza trial taken on 27 April 2000 at a golf course in the Canadian Rocky Mountains.
 

Figure 3: Trials sites for winter 2000-2001 to test the control of snow molds by a select isolate of Typhula phacorrhiza.