If you’re out in the Welsh countryside foraging with your youngsters this summer, beware coming into contact with giant hogweed.
It is an invasive and potentially harmful plant. The Royal Horticultural Society says chemicals in the sap can cause photodermatitis, or photosensitivity, where the skin becomes very sensitive to sunlight and may suffer blistering, pigmentation, and long-lasting scars.
Giant hogweed, (Heracleum mantegazzianum), is a tall, cow parsley-like plant with thick, bristly stems which are often blotched with purple. It is often found on riverbanks, but has spread inland since it was first brought to Britain by Victorian gardeners.
The flowers are white and held in umbels, (flat-topped clusters), with all the flowers in the umbel facing upwards. The flower heads can be as large as 60cm (2ft) across.
It can reach a height of 3.5m (11.5ft) and has a spread of about 1m (3.5ft).
Giant hogweed is usually biennial, forming a rosette of jagged, lobed leaves in the first year before sending up a flower spike in the second and then setting seed. True biennials only live for two years, dying after flowering, but giant hogweed does not always behave as a true biennial and may flower in subsequent years.
The RHS says when controlling giant hogweed, you should always wear gloves, cover your arms and legs, and ideally wear a face mask when working on or near it. Cut plant debris, contaminated clothing and tools are potentially hazardous too. Wash any skin that comes in contact with the plant immediately.Protect yourself from any skin contact with the sap, especially your face, when cutting stems, and carry out control measures in overcast weather avoiding sunny periods. Wash off any sap as soon as possible.
Larger scale areas are probably best left to the professionals, who should wear full protective clothing, especially if they are using a strimmer. As strimmers send sap and fragments flying, face protection is essential.
The NHS says: If you touch a giant hogweed, cover the affected area, and wash it with soap and water. The blisters heal very slowly and can develop into phytophotodermatitis, a type of skin rash which flares up in sunlight. If you feel unwell after contact with giant hogweed, speak to your doctor.