Wormwood ragweed is an exotic plant native to North America. The increase in the number of plants in the Netherlands causes various kinds of nuisance.
health problems
The high risk of hay fever complaints is the main health problem caused by Wormwood ragweed. The plant produces an enormous amount of pollen, which are also extra allergenic. Even in the presence of a single plant, the complaints can be very serious. In addition, wormwood wormwood flowers late in the season, considerably extending the period during which hay fever complaints can occur. The number of places where the plant occurs has also increased enormously in recent years, which leads to more nuisance. In addition, Alsemambrosia can give a reaction on contact with the skin, so it is best to wear gloves to remove the plant.
Danger for organic farming
Wormwood ragweed also causes nuisance in agriculture. The plants can reduce the yield and quality of low crops such as potatoes and beets due to competition for light, water and nutrients. In tall crops such as maize, sunflowers and cereal crops, there may be a loss of yield if wormwood ragweed grows in the field. The plant thrives under disturbance and low coverage by the crop grown, when plenty of sunlight is available. Wormwood is already causing major problems in southern European countries. Perhaps the most problematic is the species in Hungary, where the sunflower fields are particularly affected. Here no herbicide can be used, because Sunflowers and Wormwood are too similar.
The plant is also popping up in the Netherlands. For example, on the De Weele estate near Boekelo (OV), where in 2014 there was an explosion of wormwood plants. There is also a field near Bergeijk (NB) where the plant is proliferating. The latter case was caused by the fact that the seeds of Alsemambrosia were also present in a seed mixture for flower-rich roadsides. This has caused a large seed stock of wormwood in the field, but due to intensive management with mowing and hoeing, the seed stock is slowly decreasing. Alsemambrosia is not as much of a problem in the Netherlands as it is abroad, and we would of course like to keep it that way. However, due to climate change, the plant can also expand more and more in the Netherlands, and if we give the current plants the opportunity to form seed, this will also become an increasing problem here. That is why it is important to identify the plant at an early stage and then treat it properly.
combat
The best way to prevent the spread and nuisance of Wormwood wormwood is to prevent the plant from flowering, let alone the ability to form seeds. Seeds in the soil can remain germinating for up to forty years. Removing wormwood ragweed before it begins to flower and set seed is therefore most effective. This also prevents a lot of nuisance for people who are allergic to the plant. Be careful, because the plant can be confused with some native species, such as Mugwort and Tansy. This identification key (pdf: 9.4 MB) and video help distinguish between these two plants and Wormwood ragweed.
Report observations
The number of sightings of Alsemambrosia has increased sharply in recent years, more and more sites are being added. We just don’t always know how many plants have been found, although this is important to gain insight into the large, permanent growth sites and to combat the plant properly, for example by addressing the manager. We therefore ask that you also state the number of plants when making observations.
Webinar
On Thursday 7 July at 3:00 PM there will be an online webinar about identifying and combating Alsemambrosia. This webinar is hosted by FLORON and anyone interested in recognizing and combating wormwood the right way is welcome to participate. You can register via this form.
Help mee!
Action is needed to keep this hay fever plant under control and to reduce hay fever complaints in the autumn. Everyone can help:
Need help with recognition?
Text: Elske Koppenaal & Baudewijn Odé, FLORON; Jenneke Leferink & Johan van Valkenburg, NVWA; Arnold van Vliet, The Nature Calendar, Wageningen University; Letty de Weger, LUMC; Maurice Martens, Flora of the Netherlands; Arno Vlooswijk, Pollennieuws.nl
Photos: Arnold van Vliet, Willemien Troelstra, Johan van Valkenburg
Figure: Distribution Atlas / NDFF