Paul Backman, Tom Cook, Gwen Stahnke, and Eric Miltner

Introduction

Earthworm casting on golf course fairways is one of the most challenging turfgrass management issues facing superintendents in western Washington and western Oregon. Extensive earthworm casting on golf course fairways interferes with proper maintenance practices, playability of the turfgrass, and the overall aesthetic value of the affected fairways. Specifically, casts cause an uneven playing surface, surface sealing which reduces infiltration, and a muddy mess when the casts are mowed over (Baker, 1995).

At Washington State University Puyallup and Oregon State University, our objective is to incorporate several cultural practices into an Integrated Casting Management Program specific to the environmental conditions and earthworm species present in the Pacific Northwest. The project, which was initiated in October 1997, includes a series of short and long term field studies. To meet our objective, the initial investigation focuses on: 1) identifying which species are present and learning more about the biology of these earthworm species that cause casting problems in western Washington and western Oregon, 2) reevaluating several cultural practices that have been shown in previous research to be detrimental to earthworm activity in other regions of the world, and 3) experimenting with new strategies that have not been previously evaluated for casting reductions. This projected is funded by the Northwest Turfgrass Association and the Western Canada Turfgrass Association.

For the second phase of the project, several superintendents with severe casting problems have committed to allowing us to implement integrated casting management programs on entire fairways. We will begin this phase after the first full year of the evaluations. These integrated programs will be initiated in the spring of 1999 at Everett Golf and Country Club, Trysting Tree Golf Course, and Oakbrook Country Club.

Background

Casting occurs when earthworms ingest organic matter, leaf clippings, and mineral soil; mix the fractions within their guts; and excrete the material as casts on the turfgrass surface. It is important to note that not all species of worms in the Northwest deposit casts on the surface; many species excrete material within the profile. The seasonal pattern and severity of casting varies from year to year depending on fluctuations of temperature and soil moisture content (Baker, 1994). Casting damage is most severe during cool, wet weather in the fall and winter. This is in part because the recuperative ability of the turf is at a minimum, as the growth rate of the turf has greatly decreased.

Several environmental and cultural factors affect earthworm activity, populations, soil distribution, and species. The most critical soil properties include an adequate food supply, moisture, aeration, temperature, texture, and pH (Lee, 1985). Cultural factors can be used to manipulate the soil and turf environments to create conditions less conducive to earthworm activity. A few of the turfgrass management practices which have been reported as antagonistic to earthworm activity include the use of ammonium sulfate fertilizer to acidify the soil (Potter et al., 1985; Jefferson, 1955), avoiding lime applications in the fall (Escritt and Lidgate, 1964), clipping removal (Dawson, 1959), pesticide applications (King and Dale, 1977), and increasing sand topdressing (Lee, 1985). We will evaluate each of these cultural practices individually and in combination in attempt to develop an integrated casting management program.

Research Projects

The cultural practices we will initially evaluate include acidifying effects of fertilizers, liming, clipping removal, sand topdressing, and pesticide applications. Controlled field studies are being conducted at Trysting Tree Golf Course (Corvallis, OR), Oswego Lake Country Club (Portland, OR), and Inglewood Country Club (Seattle, WA), to look at fairway fertilization (pH), liming, and clipping removal. At the WSU Farm 5-Puyallup and the OSU Louis Brown Research Facilities we are also looking at small plot evaluations of fertilizers, topdressing sand, and clipping removal. In addition, some new strategies being tested include mustard irritants to bring the worms to the surface for physical removal, and the Rootzone Injection System to blast the worms and disrupt their burrowing system.

The initial steps for each project include soil sampling for evaluation of pH (0-2 and 2-6 cm), organic matter content, and particle size analysis. We will perform the labwork for the soil testing using an Orion SA 250 pH Meter, loss at ignition method, and the hydrometer method, respectively. In addition, earthworms will be collected from each site twice per year and identified to the species level to monitor if species shifts occur as a result of the treatments. Earthworm sampling will be completed using an extraction technique that combines hand sorting (Lee, 1985) with the addition of a mustard powder solution as an irritant (Fox, 1997). In the following sections, I describe our research plans and methods for each of the cultural practices to be evaluated in the project.

Effects of Soil pH on Casting

Several authors have reported declines in earthworm populations directly related to declining soil pH. Our objective is to evaluate the acidifying effects of ammonium sulfate, ferrous sulfate, and elemental sulfur for their ability to reduce earthworm casting.

Research was initiated in October of 1997 at three golf course sites: Inglewood Country Club, Oswego Lake Country Club, and Trysting Tree Golf Course. Each experiment is arranged as a randomized block split-plot design with four replications (two replications per fairway). Whole plot treatments include four fertilizer sources and a low nitrogen control. The whole plots are a minimum of 6 m by 27 m depending on the width of the fairway. Sub-plot treatments are half the length of the whole plots and will receive 100 lb lime/1000 ft²/yr vs. no lime.

Treatment applications are made in 0.5-1.0 lb N/1000 ft² increments to obtain approximately 4-5 lb N/1000 ft²/yr. Supplemental applications of potassium and phosphorous will be made equally to all treatments using muriate of potash and diammonium phosphate. Below is a list of the treatments:

Whole Plots:

• Ammonium Sulfate (21-0-0) (24% Sulfur) Elemental Sulfur (99.5% S) + Urea (46-0-0)
• Polymer Coated Urea (44-0-0) (43-0-0) (42-0-0)
• Control (low nitrogen with no sulfur)

Sub Plots:

• Lime at 100 lb/1000 ft²/yr (applications made in 25 lb /1000 ft² increments)
• No lime

In this study, we will use earthworm casting counts as an indirect measurement of earthworm activity. The counts will be completed using a 1 m x 1 m frame quadrant (constructed of 1.5 inch PVC) divided into 25 sections. Castings will be counted on four-week intervals during the fall and winter months when casting damage is severe. A total of eight random counts will be made from each plot, four per sub-plot. Visual analysis of turf quality will be made three times per year on a scale of 0-9, with nine being highest quality.

The earthworm species Lumbricus terrestris has been identified as the main casting source at all three golf course sites. This species typically burrows deep within the soil profile. However, due to regular irrigation and constant food supplies (clippings) on fairways, they tend to remain active near the surface. Initial pH’s from the three courses taken in October ranged from 5.6 to 6.3 at 0-2 cm and 5.8 to 6.4 at 2-6 cm. PH measurements will be taken again in October 1998. Initial casting counts were taken in October and February of 1997. Casting counts will be taken monthly from October through February 1998.

Effects of Clipping Removal on Casting

Earthworms feed on dead and decaying plant material and the free bacteria and fungi present during the decay of the tissue. Previous research has shown that the amount of food on the surface can directly influence earthworm populations. The goal of our research is to determine if clipping removal from fairways will reduce earthworm castings in the fall and winter.

Two projects will be conducted. First, a project at Oswego Lake Country Club has been set up with four replications, one replication per fairway. Plots are approximately the width of four passes of a triplex mower (6 m) by the width of the fairway. The treatments include clippings removed using the triplex approach mowers and clippings returned with the fairway mowers. Ratings will be taken at four-week intervals using the same procedures as the soil acidification study. This trial was initiated in May of 1998. The second project will be established at Farm 5 in September 1998 and will look at clipping removal with a combination of other treatments which are yet to be determined.

Effects of Sand Topdressing on Casting

Worm populations are greatest in light and medium loams, with smaller populations in heavy clays and coarse sands. It is believed that the abrasiveness of sand particles and their susceptibility to drought influences both species composition and earthworm numbers in the soil (Lee, 1985). Our project will evaluate sand topdressing at a rate of 3/4 inch sand/year in combination with other treatments to determine if sand is an effective cast reducer, and if so, the amount of sand required before a reduction is observed.

The trial was established at the WSU Farm 5 in Puyallup, WA. The treatments are arranged in a randomized complete block design with three replications. Plots are 1.5 m by 1.5 m, and ratings will be completed using the 1m x 1m frame quadrant device, which will be placed, in the center of the plot, providing a 1 m buffer between plots.

Conclusion

Earthworm casting is a very serious problem on many golf courses in the Pacific Northwest. There is an urgent need for management programs that create a less conducive environment for earthworm activity and casting, while still maintaining quality turf. Our goal of designing a casting management program for golf course superintendents is achievable but will take some time and coordinated efforts. In the initial phases of this project, we have learned a lot about the biology of these organisms, in particular the species which deposit casts on the turfgrass surface. There were no immediate reductions in casts on the surface from the fertilizer or sand treatments. This fall and winter, when casting is most severe, we will be able to asses a full years worth of treatment applications.

References

• Baker, S.W. 1994. Aeration, earthworm control and golf standards: aspects of sports turf research in the United Kingdom. New Zealand Turf Management Journal. May, 5-6.
• Baker, S.W., J.A. Hunt and E.C. Kirby. 1996. The effect of soil acidification on casting by earthworms. I. Preliminary trials using sulfur and aluminum sulfate. Journal of Sports Turf Research Institute. 72:25-35.
• Dawson, R.B. 1959. Practical Lawn Craft and Management of Sports Turf, 5th Edition, Crosby Lockwood & Son, Ltd. London, 320 pp.
• Escritt, J.R. and Lidgate, H.J. 1964. Report on fertilizer trials. J. Sports Turf Res. Inst. 40: 7-42.
• Fox, C.A. 1997. Extracting earthworms from soil. http://res.agr.ca/lond/pmrc/faq/wormsoil.html.
• Jefferson, P. 1955. Studies on the earthworms of turf. A. The earthworms of experimental turf plots. Journal of the Sports Turf Res. Inst., 9: 6-27.
• King, J.J. and J.L. Dale. 1977. Reduction of earthworm activity by fungicides applied to putting turf. Arkansas Farm Research. 26 (5): 12.
• Lee, K.E. 1985. Earthworms. Their Ecology and Relationships with Soils and Land Use. Academic Press, New South Wales, Australia, 411 pp.
• Potter, D.A., B.L. Bridges, and F.C. Gordon. 1985. Effect of N fertilization on earthworm and microarthropod populations in Kentucky Bluegrass turf. Agronomy Journal. 77: 367-372.