Wormcast Problems for Turfgrass Managers

worm

Earthworm activity is becoming a significant challenge  for sportsturf managers across the UK, Ireland and increasingly across the US and Canada. With the absence of chemical controls, greenkeepers and sportsturf managers are searching for alternative control methods. This article discusses the dual nature of earthworms: their benefits to soil health and the negative aspects of excessive casting on high-quality turf surfaces. We delve into earthworm biology and assess scientific findings on current management strategies for casting. 

Ecological functions of earthworms.

There are 26 earthworm species identified in the UK, and up to 76 species in North America, the majority of these species do not produce surface casts, however, a minority of species do result in casting, potentially troubling for managed amenity areas and fine turfs. Earthworms  are essential to the ecosystem, enhancing soil structure by burrowing and breaking down organic  material, enriching and aerating the soil.  

In golf course management, where moist soil and organic matter are abundant, earthworms can greatly benefit turfgrass systems by preventing thatch buildup, promoting soil health, and enhancing water infiltration.

However, excessive casting on the surface complicates turfgrass maintenance, affecting playability, increasing susceptibility to weeds and diseases, impairing mowing efficiency, and diminishing the visual appeal of sports turf. The challenge lies in balancing the ecological benefits of earthworms with the practical needs of maintaining high-quality turf surfaces, necessitating a thorough  exploration of effective, sustainable management practices.

Controlling casting.

Until recently, surface casting was controlled by the use of a number of chemical options, these options have been withdrawn in many legislative areas leaving turf managers searching for viable alternative control strategies. Earthworm control in the past, that is from the early 1900s, firstly relied on Mowrah Meal, derived from the seeds of Bassia latifolia, which, when watered into the soil, irritated the earthworms, causing them to come to the surface where they were physically removed.

From the 1950s, controls involved a number of highly toxic chemicals, which John Dempsey PhD Wormcast problems for turfgrass managers although highly effective in controlling surface casting, were extremely hazardous to the  environment and humans. These included: copper sulphate, potassium permanganate, derris  dust (an extremely poisonous chemical to invertebrates), lead arsenate, and mercuric chloride  (extremely poisonous to humans and to other mammals).

In the more recent past: chlordane (organochlorine), was used from the 1960s to the early 1980s – very persistent in the soil lasting up to seven years or more in certain soil types such  as heavy clay-based soils, carbaryl and thiophanate methyl. Carbendazim, which was primarily sold as a fungicide, targeted casting species only, results were variable, but it was the mainstay for cast suppression and remained in use until recently. It was the withdrawal of  carbaryl that caused the current widespread concern among turfmanagers.

Research in worm cast controls.

With no effective chemical controls many turfgrass managers have resorted to brushing,  especially when conditions are dry and/or the use of rotary mowers which breakdown and  distribute the casting materials. 

What methods can be used to control earthworm castings, and how effective are they? Several strategies have been proposed and studied in recent years to manage earthworm castings.

Cultural controls have been  investigated as a way to suppress casting activity. These methods include removing grass clippings to decrease organic matter, thus reducing earthworms’ food sources, using acidifying fertilizers, and topdressing with angular sands or abrasive aggregates. 

Surface acidification

Surface acidification requires the application of compounds such as sulphate of ammonia,  ferrous sulphate, and sulphur. The Rutgers study mentioned above produced interesting and  relevant results in this area. They concluded that elemental sulphur applications had the most  rapid and dramatic effect, reducing earthworm casting within the first season of application  by as much as 97%, compared to untreated plots. The potential to scorch turf was a concern  with applications of elemental sulphur. Researchers initiated trials to identify the maximum  rate that can be applied without risk to the turf rates of 146 kg/ha elemental sulphur in a  single application during spring or late summer without damaging fairway turf. They found  the combination of sand topdressing and elemental sulphur was the most effective treatment  in their trials. 

Researchers at Rutgers University

explored various strategies to reduce castings, such as using different fertilizers, liming, sand topdressing, elemental sulphur applications, and a  combination of sand topdressing with sulphur. The study suggested that the effects of  fertilizers on casting became noticeable only after several years, with organic fertilizers  tending to increase castings and synthetic ones showing minimal effects. Despite the mixed effective in areas with high casting activity, reducing castings by 50% over three seasons in  specific cases, such as certain golf courses.

Research led by Paige Boyle, Ph.D.,

at Utah State University examined turfgrass ecology  and casting on fine turf surfaces and concluded that sand topdressing initially exacerbated  casting issues, contradicting previous studies that suggested a decrease in castings with topdressing. The study emphasized the importance of a consistent and prolonged topdressing regimen to observe positive outcomes. 

A Penn State University study found that measures like removing grass clippings and hollow-core aeration did not decrease casting volumes significantly. Instead, the study highlighted that saponins showed the most positive results, while sand topdressing did not have a consistent impact on reducing castings and could sometimes even increase them.  

Saponins

Products containing saponins derived from tea seed meal are now being marketed for turf  applications in countries like the UK and Ireland. When used as expellents, saponins irritate  earthworms disrupting the mucous coatings on earthworms, leading to their dehydration and  eventual demise. Studies at the University of Kentucky showed that a single tea seed meal application reduced castings by over 95% for at least five weeks. In another trial at the same location, casting was reduced by 98% after two days and by 83% after 30 days following tea seed application. 

For optimal results, saponin  treatments should be watered deeply into the soil and applied before each casting peak due to their limited residual effectiveness.  

Additionally, it should be considered that earthworms hatching from cocoons are not affected  by these treatments and may repopulate the area gradually.

Conclusion:

Earthworms are an important component of ecosystems – vital for healthy soils! They have  beneficial effects on soil structure, organic matter recycling and provide food sources for  many species. 

With the withdrawal of all chemical controls a number of other options have been explored  with a view to cast suppression. These include reduction of organic matter, sand topdressing,  surface acidification and the use of saponins. Of these, long term sand topdressing combined  with surface acidification with sulphur appears effective. The use of saponin-based products  also appears to effectively suppress castings, but these treatments need to be applied  frequently during peak activity. 

To date there have been outstanding results in ways to reduce casting. Trials remain underway searching for an ecologically friendly and sustainable means to solve this problem,  at the moment none are showing positive results, but the search continues!

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