“Here’s looking at you, kid,” is not in the script of the movie Casablanca, first seen in U.S. cinemas in November 1942.
It is said that Humphrey Bogart ad-libbed the words in conversation with his co-star, Ingrid Bergman, and Director Michael Curtiz decided to leave them in the soundtrack. Whatever the truth of that, the word ‘you’ is deliberately rendered as ‘ewe’ in the title of this piece, for it is about giant hogweed. Are you with me so far?
In February 2008, I wrote these words: “Pick up any book about British wildflowers and you won’t have to read many entries on plant genera, species and sub-species before you encounter phrases like, “garden escapee”, “escaped from cultivation” or “has become widely naturalised”. These phrases mean what they say … that the family of plants in question, or a specific member of that family of plants, is not native to the United Kingdom but came here as an immigrant and has become established in the British countryside, where it has found the conditions to its liking.”
And one of the plants which has found conditions in the United Kingdom very much to its liking is giant hogweed - Heracleum mantegazzianum to give it its Sunday name. A native of the temperate areas of eastern Asia, this tall waterside plant was originally introduced into this … and many other European countries … by enthusiastic gardeners in search of exotic plants to make their gardens more exciting and more special than those of their neighbours. But giant hogweed spread into the countryside, finding lots of streams, waterways and rivers where it could flourish, where its tall height allowed it to form dense stands, often stifling native plant communities. And, being non-native, it was thought to have no natural enemies in most European countries and was able to spread virtually unrestricted even by the owners and by the users of waterways, for another of its endearing characteristics is that the seeds germinate very readily, so that it was seen as being virtually impossible to eliminate the problem once the plant had colonised an area.
But surprisingly late in the day, a Danish academic paper catchily entitled, “The giant hogweed best practice manual. Guidelines for the management and control of an invasive weed in Europe,” by C. Nielsen, H.P. Ravn, W. Nentwig & M. Wade has come to the attention of the British media. First published in 2005, this paper reviewed research which - and I quote, “showed that grazing with domestic livestock is a very effective method of control of large stands of invasive hogweed. Evidence for the effects of grazing came mostly from the use of sheep, but giant hogweed is also very palatable to cattle. These grazers eat most above ground plant parts, thus greatly reducing photosynthesis and depleting energy resources stored in the root. Sheep and cattle prefer young and fresh plants, and the most efficient control is obtained by commencing grazing in the spring when the plants are small.”
So giant hogweed actually does have natural enemies in Scotland – sheep! By nibbling the young shoots … and the landowner needs to cut down established plantations of the stuff to allow young, fresh plants to spring up … the sheep keep the ground clear of this invasive plant, allowing the native grasses to re-establish themselves and so encourage grazing by other species of farm animals, which in turn inhibits the facility for hogweed seeds to germinate and grow. And, while few large-scale gardeners who have regretted introducing giant hogweed into the wetland areas of their estates will want to bring in sheep to deal with their problems, I expect that many land-owners will be very interested in this development.
Sandy Simpson, Polmont Horticultural Society