Catchment News

Tackling Invasive Species in Offaly

Knotweed is Priority for Offaly

The focus for work on invasives in Offaly is predominantly on Japanese knotweed with two sites of Himalyan balsam. We are very fortunate that we do not have the task of tackling Gunnera or Giant hogweed. There are a small number of recorded patches of Gunnera, still in the original setting where they were planted. We are examining Himalayan balsam along the Camcor river in 2017 which is of increasing concern.

Recording, Monitoring and Awareness

The vast majority of the Japanese knotweed sites in Offaly are roadside with just a couple of sites along riparian zones beside waterbodies. This makes treatment easier as access, permissions, monitoring and health and safety are more straightforward than riparian work. We work closely with NPWS rangers, the botanical recorder for the Botanical Society for Britain and Ireland (BSBI) in Offaly and the Offaly Naturalists’ Field Club to monitor the range of invasive species. We have been promoting awareness of invasive species since 2008 when we held Biodiversity Training for Offaly County Council staff. The first key message was ‘Do Not Disturb’ as it was clear that hedge and verge cutting was a factor in the spreading of knotweed. Staff throughout the Council have reported sites with litter wardens, clerk of works, area engineers and roads teams all being to the fore. This has resulted in close to 40 sites being logged for treatment.

Treatment – Persistence is the key!

We commenced county wide treatment and 2017 will be the fourth year. Persistence is definitely the key! Having sprayed in 2014 there was practically no re-growth in 2015 except for one or two shoots emerging at the edge of treated patch where the rhizomes (continuously growing horizontal underground stems which put out shoots and roots at intervals) may not have been reached the previous year. However in 2016 we had some shoots of weak, knarled growth at a number of the sites. They have all been treated again and we wait to see what happens in 2017. Stem injecting is the most effective treatment but it is very time and labour intensive. We have done this at a couple of sample sites and also at one site adjacent to a river as Synero is not recommended close to water. We have been spraying with a number of different brands for the past three years. All have been effective to varying degrees. We find that Synero has the advantage that it can be effective when sprayed during the summer as well as after flowering in late September.

Awareness

We issue Facebook posts, newspaper articles and do radio interviews to raise awareness and for the past number of years we have included information about Japanese knotweed in the hedge cutting notices to landowners. The Offaly Tidy Towns network is also a key group that we work with. As Heritage Officer I will call to private landowners if knotweed is on their land and check the land register to contact them otherwise. This is not so practical perhaps in other counties where there is a much higher density of sites but our aim has been to tackle the matter before it became a major problem. Once information has been given to landowners the success rate of dealing with it is very high. There has been a definite change in awareness in the past five years with the vast majority of people I have called to now being aware of the issue of Japanese knotweed but perhaps not recognising it as being on their land. This has been greatly assisted by national media running a number of features. In 2016 the Council put up notices at East Offaly sites to draw attention to the locations. These are on 1.5m high metal post with permanent signs that certainly are being noticed by passersby, but also by drivers of hedge cutting machines. This is also important as while we may achieve no re-growth above ground, we do not know what condition the rhizomes are in – they may be stunned but not dead. Ongoing monitoring is essential and awareness of the location of treated sites so that they are not disturbed accidentally thus spreading the rhizomes.

Amanda Pedlow, Offaly Heritage Officer