Controlling alien species

The control of the alien species of hogweed plants and the copper tops is currently organised nationwide


The most effective measures of combating alien species are the early detection of alien species, the rapid dissemination of information, and the rapid eradication of the alien species at an early stage of their spreading.


SOSNOWSKY’S HOGWEED. Photo: Eike Tammekänd
SOSNOWSKY’S HOGWEED. Individual Sosnowsky’s hogweed plants are easier to expulse than large colonies. Photo: Eike Tammekänd


However, if the species is already so widespread that eradication is no longer possible, control measures must be put in place. These are either lethal or non-lethal physical, chemical, or biological measures applied to expulse an alien species or to limit its population [1]. Pursuant to the Nature Conservation Act, the Environmental Board organises the regulation of the number of specimens of alien species that have entered the wild. Currently, the control of two species – hogweed alien species (giant and Sosnowsky’s hogweed) and the copper tops – is organised nationwide. The mentioned plants are aggressive alien species, but their spread can still be limited and they can be removed from the wild. Catching alien fish or crustacean species from the aquatic environment is much more difficult, if not virtually impossible. Hogweed plants are also dangerous to human health.


In Estonia, the national control of hogweed began in 2005 and since 2011, it has been based on a management plan. While in the first year, data were collected and control was performed locally, in 2006 it expanded across Estonia, regardless of the ownership and purpose of the land. By 2021, control measures had already been taken on approximately 2,500 hectares [2]. As the hogweed has been controlled for more than a decade, the viability of the colonies is already declining. This can be considered very successful, as without control work, the area of distribution of the hogweed would currently be at 7,000 hectares [3]; in Latvia, the area is about 10,000 hectares, according to the estimates. As of the end of 2021, hogweed had been declared extinct on 622 hectares and about a third of the colonies subject to control measures are on the verge of extinction [2]. Depending on the size of the hogweed colony, the control method is also chosen. For smaller areas and single plants,  pulling out the roots is recommended. In the case of larger colonies, manual poisoning is carried out [4]. In the fight against the hogweed, it would be helpful if the eradication of smaller hogweed colonies on private land was the responsibility of the landowner themselves. However, it must be kept in mind that hogweed sap is poisonous and, combined with exposure to light, can cause burns. Therefore, skin contact with the sap should be avoided and gloves should also be washed thoroughly after work [5]. Between 2005 and 2009, more than 20 million kroons (approximately 1.32 million euros) were spent on the control of hogweed plants [6]. Since 2010, the Environmental Board has commissioned works on the basis of a public procurement, which has reduced the cost of control, and in 2021, the budget was almost 400 000 euros [7]. Currently, the control of the hogweed is financed from the state budget.


In 2018, the management plan for the copper tops was approved. Although a beautiful flower, its rapid spread threatens native species. The copper tops is known to have spread across about 200 hectares, but is likely to be even more widespread. The copper tops is easier to control than a hogweed: it can be eradicated by uprooting the plants (or weeding, mowing, grazing, as well as by treating them with boiling water). The control of the copper tops begun in 2018 and initially it was done through campaigns, with the help of volunteers or community service workers. For the years 2019–2023, a total of approximately 35,000 euros is planned for the control and related activities on the basis of the management plan.


Prevention of the spread of alien species


The best way to prevent the spread of alien species is to not bring them to Estonia – this applies to mammals, birds, fish, as well as invertebrates and plants. An individual also has a great responsibility here: alien species must not be intentionally or unintentionally brought to Estonia or introduced into the wild here; pets must not be released into the wild either, although they (like the red-eared slider) might fare well in Estonia’s warmer winters. Alien earthworms and baitfish used for bait in fishing can also enter and survive in the wild.


Garden owners should prefer domestic species or ensure that no alien species are introduced into the wild with compost, garden scraps, or otherwise. When growing an alien species, you must first make sure that it is not included in the list of prohibited alien species. The roots and soil of plants imported from abroad must be inspected and it must be verified that no diseases or passenger animals have been brought along.


For example, the Portuguese slug has been brought to Estonia with planting material and it is highly likely that it is impossible to eradicate. For control, it is recommended to collect the slugs and pour boiling water over them [8], but chemical control agents are also available. The easiest way would be to check the soil brought into the garden and create conditions that are unfavourable for the reproduction of slugs (ash, mulched grass, ploughing the soil). If the slug already exists in the garden, it is important to start controlling or picking the slugs immediately in the spring in order to catch as many slugs as possible before they reproduce, so that the late summer slug flood can be avoided.


Additional information: the handbook on aquatic alien species and the handbook of terrestrial alien species.



Last modified: 17.03.2022



[1] EL määrus looduslikku tasakaalu ohustavate võõrliikide sissetoomise ja levimise ennetamise ja ohjamise kohta

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[5] Keskkonnaamet. 2019. Karuputke võõrliikide tõrje- ja ohutusjuhend.

[6] Holm, B. 2010. Karuputke (Heracleum) võõrliikide ohjamiskava. MTÜ Pärandkoosluste kaitse ühing. Tartu. 

[7] Võõrliikide tõrje 2019. aastal. SA Keskkonnainvesteeringute keskus

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