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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Friday 23rd March 2012

Heracleum mantegazzianum, giant hogweed

Heracleum mantegazzianum, giant hogweed
The way it used to be

The Tweed Forum Invasives Project (TFIP) has published its latest annual report The project is primarily concerned with Heracleum mantegazzianum, giant hogweed, and Fallopia japonica, Japanese knotweed, though it is, as far as possible, also trying to address the situation with Impatiens glandulifera, Himalayan balsam.


Though Japanese knotweed is a threat to infrastructure because of the strength of its roots and Himalayan balsam crowds out native plants, it is only giant hogweed that causes physical harm to humans so that is the plant I’m interested in.


I always talk about the idea that seeds of Heracleum mantegazzianum stay viable for up to seven years so any eradication programme has to be of that duration but, since this is the ninth annual report from TFIP, that has to be seen as a minimum.


Heracleum mantegazzianum, giant hogweed

Heracleum mantegazzianum, giant hogweed
In April 2004

The report is reasonably upbeat stating that invasives control has been delivered and that coverage of giant hogweed is greatly reduced though its map of coverage still has one small stretch of the Whiteadder Water where it is coded as ‘Abundant’ and five other short stretches where it is defined as ‘Dominant’. Quite a lot of the total is marked ‘Frequent’; by eye I’d say around 10-15% of the length.


The report makes clear that vigilance is still required in walking the whole network until such time as it is possible to be completely sure that there are no plants anywhere but it points out that a reduction in the amount of chemicals used for spraying demonstrates its success in reducing the number of plants.


The control programme starts in mid-April but, given the early start to growth this year, I wonder if more spraying will be required in 2012 as plants will be larger by the time contractors reach them.


Heracleum mantegazzianum, giant hogweed

Heracleum mantegazzianum, giant hogweed
In February 2012

Reading between the lines, there does seem to be a problem with cost control. I would assume that, when giant hogweed was more prevalent, you could make a correlation between chemicals used and contractors’ time but, with more time now being spent walking the ground in search of plants, it seems it is harder to verify the claims made by contractors. Indeed, the final section of the report ‘Tactics for 2012 control season’ begins with saying ‘we will make sure contractors tighten up their reporting in terms of what time they have spent where’ though it suggests this is more to do with correctly recharging costs to the responsible landowners than an inference that false claims are being submitted.


As someone who has walked the Tweed for some ten years, I know that there is far less Heracleum mantegazzianum than there used to be and the days of having to abort a walk because the paths were overrun are gone. It is good to know that the TFIP is aware of the need to use its money wisely because there is, clearly, a danger that someone could decide the job is done and scale back its operations.