Earthworm Casting on Golf Course Fairways (1998)
Paul Backman, Research Associate in Turfgrass Washington State University - Puyallup
Complete elimination of earthworms, even if it were possible, is not our objective. We must remember that earthworms provide far more benefits to the soil/turf environment that they do harm. The earthworm's burrowing and feeding activity initiates thatch decomposition, stimulates microbial activity, makes certain plant nutrients more available, increases soil aeration and in general improves overall soil quality. Our intention is to develop and Integrated Management System for reducing casting that (1) will initially reduce the size of the earthworm populations under the fairways, and (2) modify the soil environment so it's not so conducive to supporting an enormous earthworm carrying capacity.
After one full year of treatment applications through June of 1999, the cultural factors of increasing soil acidity, applying 5/8" sand topdressing and clipping removal has no significant effects on reducing earthworm casting. We have observed significant reductions in casting with the applications of three commonly used pesticides for both European Cranefly and fusarium patch disease. The more labor intensive practice of physical removal has also shown to be effective for immediate reductions in earthworm populations.
The issue of earthworm casting is one that surfaces over and over again in pro shops, clubhouses, and board and green committee meetings. At the heart of the issues is the "quality of turf" and how casting affects the type of lie a golfer has on the fairways.
Fairway casting, when severe enough, can affect the implementation of summer and winter rules, with earlier winter rules initiated in the fall and a later start on summer rules in the spring. The golfers and club members who prefer to "play the ball down" year round tend to be the most vocal about earthworm casting.
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Development of an Integrated Management System to Reduce Earthworm Casting on Golf Course Fairways (2000)
Washington State University: P.A. Backman, E.D. Miltner, G.K. Stahnke, and Oregon State University: T.W. Cook
There are no products designed or registered specifically for control of casting. Development of other strategies to reduce casting is critical; cultural factors must be evaluated as options. The cultural factors of clipping removal, hollow-core aeration, and acidifying fertilizers evaluated in this study had no impact on reducing earthworm casting caused by L. terrestris in the Pacific Northwest. Sand topdressing proved to be effective at reducing casting.
With clipping removal, it is possible that modifying the environment with these same cultural factors over a much greater period of time could have an impact on the reproduction rate of L. terrestris earthworms by effectively lowering the food supply and earthworm carrying capacity of the soil. Mature L. terrestris can produce hundreds of offspring each year. These offspring can reach maturity in one year and then begin reproducing. The fact that L. terrestris earthworms have been reported to live easily for up to 6-9 years in the soil means that modification of the soil/turf environment from some treatments may need to be in place for numerous years before the earthworm population decreases and casting reductions are observed.
The effects of increasing soil acidity had no impact on reducing casting. The response curve of earthworms to various soil factors is not the same for all earthworm species. The species of Aporrectodea calignosa, and Aporrectodea longa are much more intolerant of acidic conditions than L. terrestris. In addition, most earthworm species tend to remain in the top few inches of the soil, whereas L. terrestris burrows deep into the soil and is constantly moving up and down in the soil profile based on temperature, moisture and atmospheric pressure. This constant movement takes them out of the upper soil depths, where most of our treatment effects from soil acidity are observed. Likewise, an increase in casting was not observed after 2 years of heavy lime applications.
It has been reported that the abrasiveness of sand particles and sand's susceptibility to drought influences both earthworm species composition and earthworm numbers in the soil. In this project, sand topdressing resulted in dramatic reductions in earthworm casting after one growing season of sand topdressing. However, to achieve the full benefits of a fairway sand topdressing program, the objective is to apply a minimum of 1" of sand per year over 5 years. That program is recommended versus a one-year program for casting control. A second long-term project will be initiated with larger plots. As a side note, on the high sand plots (1.5" sand) we did observe an increase of fusarium patch through the fall and winter. The disease was a result of the increased shoot density on the high sand plots coupled with the new tissue being generated as the crowns were continually being covered with sand.
The issue of earthworm casting will continue to be a difficult management issue in the future. It is very unfortunate that there are superintendents that face extreme pressure from pro shops, members, and boards. After all, these earthworms prefer the same conditions that are required to maintain healthy turfgrass. For superintendents, it is extremely important to educate the parties involved on the biology of earthworms, benefits of earthworm activity, and the lack of products available for control.
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