Invasive plants: fleabanes
Canadian fleabane (Conyza canadensis or Erigeron canadensis) and annual fleabane (Erigeron annuus or Stenactis annua) are annual herbaceous plants belonging to the Asteraceae family and originating from North America. They exhibit all the characteristics of invasive nectar-producing plants: exotic origin; rapid growth; production of a large number of wind-dispersed seeds that can be transported over several kilometres; ability to germinate in the smallest crevices; and strong attractiveness to pollinating insects, including honey bees.
Although they are no longer marketed, they have become naturalised very rapidly throughout Europe since their introduction for ornamental purposes in the 17th century. Today, they constitute a real threat not only to ecology but also to the economy. These plants spread massively and form dense, monospecific stands that reduce biodiversity and the forage value of fields, not to mention the loss of floral diversity for bees.
Canadian fleabane bears a large number of tiny flowers that bloom from June to October; its hairy stem is highly branched at the top, and its leaves are also velvety. It is an edible plant that can be consumed raw or cooked and also has medicinal properties: its flowers and essential oil have anti-inflammatory and analgesic effects that are beneficial in cases of rheumatism.
Annual fleabane grows to a height of 30 to 100 cm, sometimes even up to 150 cm; its flowers, very similar to those of daisies, form a true floral carpet from June to October. The plant produces secondary metabolites that inhibit the germination and growth of surrounding plant species (allelopathy), thereby increasing its harmful impact on biodiversity.
Both species are very common in Valais, where they invade – in the subalpine zone – meadows, gardens, rubble, paths, railway lines, and warm, dry sites. As the nuisances caused by these plants far outweigh their benefits, it is essential to take all necessary measures to prevent their spread!
Sources
Infoflora.ch
J. Piquée, Melliferous plants month by month, 2014
2302_18 Cantonal concept for the control of neophytes.pdf