The difficult journey of the control of alien species: the giant hogweed and Sosnowsky’s hogweed in Estonia?

Systematic control of alien species in Estonia began with two species of hogweed: the giant hogweed and Sosnowsky’s hogweed. They were brought to us mainly as silage during the Soviet era, but have proved to be troublesome nuisances that have now been controlled for more than a decade.

The giant hogweed and the Sosnowsky’s hogweed are exceptionally mighty, their seed production is enormous (up to 100,000 seeds per plant), and the seeds are able to germinate in the soil after up to 10 years. Due to the very durable seed and powerful storage root, it is quite difficult to get rid of the giant hogweed and Sosnowsky’s hogweed. If allowed to reproduce and grow undisturbed, these species can occupy areas of several dozen hectares. No other plant species usually grows in these large colonies. Thus, they are alien plant species that pose a serious threat to our natural balance.

In addition, the giant hogweed and Sosnowsky’s hogweed are dangerous to humans because their sap contains substances that, when exposed to the sun, can cause severe burns to the skin. If the sap gets in your eyes, it can cause blindness.

Hogweeds have been controlled for more than a decade

As the giant hogweed and the Sosnowsky’s hogweed are dangerous to nature and humans, it was decided in 2003 that they should be eradicated. Initially, control measures were launched in Tartu County and Viljandi County. By 2006, control activities had been extended to the whole of Estonia, although it was not done in all colonies, but on about 605 hectares. Since 2010, national control has covered all known colonies. Thus, in 2010, almost 1,300 hectares of alien hogweed species areas were mapped all across Estonia. In February 2019, however, about 2,700 hectares of such areas were known. At present, more than 400 hectares of colonies have been destroyed, but these areas must be constantly monitored.

There are three methods used in the national hogweed control programme:

• manual poisoning,
• uprooting the plants,
• cutting the inflorescences.

The most common is manual poisoning with a glyphosate-based herbicide. This is often the most practical method, as in most cases, the control activities must be carried out in a very large number of areas and in a relatively short period of time. Efforts have been made to increase the share of plant uprooting as the most effective method. This method is the only possible option in water protection zones, on organic arable land, in outdoor areas, near childcare facilities and beehives, and is best in small and sparse colonies. Inflorescences are cut in very few occasions, because it requires precise timing. The controller must follow the work and safety instructions.

In addition to hogweed alien species, other foreign plant species that threaten our nature have been spreading in Estonia, such as the copper tops and the rugosa rose. They, too, need attention and control, but unfortunately the state lacks money.

Full article in the March 2019 issue of Eesti Loodus, pages 50–60, http://www.eestiloodus.ee/arhiiv/Eesti_Loodus03_2019.pdf

                                                                                                                     By: Eike Vunk

                                                                                                                     Edited for Loodusveeb by: Reigo Roasto