Inadequate drainage, soil compaction, reduced fertiliser use, and increased rainfall levels could be causing rush infestation in upland areas, according to a group of scientists.

The researchers from Lancaster University, Natural England and the University of Liverpool state that increased rush covers are having a negative impact on the agricultural and environmental value of marginal grasslands.

As part of a study published in the scientific journal Annals of Applied Biology, satellite images of the West Pennine Moors in northwest England were surveyed over a 13-year period.

The study found that the area of land covered in rushes had increased by 174%. In 2005, 57% of plots had no rushes, but this had reduced to just 35% by 2018.

Rush dominance results in a reduction in grassland biodiversity and farm productivity

The scientists state that the findings are consistent with anecdotal evidence from across the UK that rush covers within marginal grasslands have “increased considerably in recent decades”.

“Rush dominance results in a reduction in grassland biodiversity and farm productivity,” the researchers confirm.

Previous studies have found that a 15% rush infestation in a grassland sward can reduce annual grass yields by 1.25tDM/ha, which brings an estimated economic cost of up to £78/acre/year.

Increased rush covers also lead to declines in plant and bird biodiversity in upland areas. For example, grasslands where rush covers exceed 30% becomes a suboptimal nesting habit for wading birds.

A single rush stem can produce between 4,500 to 8,500 seeds each year

Rushes grow in wet, acidic soils and their seeds can remain dormant for up to 60 years. A single rush stem can produce between 4,500 to 8,500 seeds each year, which can lead to over 4m seeds per square metre on rush-infested ground.

Various reasons are suggested by the researchers for the recent increases in rush covers. They include the high cost of drainage, low stocking rates, and reduced management intensity (often due to the terms of agri-envionment schemes) resulting in lower applications of fertiliser, manure and lime.

The move away from grazing native cattle and cutting fodder, could be detrimental to rush control

Also, upland farmers now mainly focus on keeping sheep, which tend to be more selective grazers than cattle. The move away from grazing native cattle and cutting fodder, could be detrimental to rush control, the research paper states.

Finally, climatic factors could be at play too. The researchers quote Met Office data which shows north west England was 3% wetter between 2005 and 2018 than it was between 1981 and 2010, and there was 7% more rainfall than in 1961 to 1990.