Fears rise over Kiwi flatworm threat to crop yields

New Zealand flatworm

Declan O'Brien

April 06 2021 02:00 AM

An unwanted Kiwi visitor could seriously reduce grass and crop yields on Irish farms by undermining the organic matter content of soils.

The New Zealand flatworm (arthurdendyus triangulates) can cut grass yields by around 7pc as a consequence of their impact on the native lobworms or large earthworm, experts have estimated.

The invasive species feeds on the unfortunate earthworm and can reduce numbers by up to 70pc where infestation levels are particularly high.

Since first being identified in the Belfast area in 1963, the New Zealand flatworm is now found throughout most of Northern Ireland and much of the South.

Dr Archie Murchie of the Agri-Food and Biosciences Institute in Belfast said Fermanagh was the only county in the North that did not appear to have New Zealand flatworms.

While the exact level of infestation nationally is not known, Dr Murchie said reports from the general public suggested that the flatworm was “pretty widespread” in coastal counties, where it is prevalent in gardens in most towns and villages.

Research in the North found that while the New Zealand flatworm was present in just three of 75 fields surveyed in 1991, eight years later this figure had increased to 60 fields.

A similar level of spread has been noted in the South, according to Dr Michael Gaffney of Teagasc.

The main impact of the flatworm from a farming point of view centres on the reduction in lobworm numbers.

Given the importance of the earthworm in regenerating soils, a severe infestation of flatworms reduces organic matter content and consequently hits the ground’s yield potential.

Dr Murchie said grass yield could be reduced by around 7pc because of the “hit to biomass”. While he said that this was “purely a calculation”, he pointed out that earthworms were “pretty beneficial to the soil and the recycling of nutrients”.

Since the New Zealand flatworm has few natural predators in Ireland, apart from ducks and some beetles, there is no way of controlling numbers.

Native earthworms face a further threat from the Australian Flatworm, which is also present in Ireland and Britain. Smaller than the New Zealand flatworm, the Australian variety tends to operate in groups, Dr Gaffney said.

“The National Biodiversity Centre has started compiling records for both [the New Zealand and Australian flatworm] in the last few years and I encourage people to report their findings to it as it’s probably the best way to fully appreciate how widespread this pest actually is,” Dr Gaffney said.