Hessian experts warn against a further spread of the heat-loving ragweed plant because of possible allergies. "It is increasingly becoming a health problem", says Aljoscha Kreb from the Climate Change and Adaptation Center of the Hessian State Agency for Nature Conservation, Environment and Geology (HLNUG) in Wiesbaden.
The pollen of the mugwort ambrosia could trigger serious respiratory allergies and even asthma in sensitized people. The plant is benefiting from man-made global warming.
Low concentrations are sufficient for allergic attack
Originally, ragweed artemisiifolia (mugwort), as it is scientifically called, originated in North America. It is "a newcomer with a particular health hazard", judges the Julius Kuhn Institute, a research institution of the federal government.
"Even people who are not otherwise allergic to pollen can develop an allergy." Even low concentrations of five to ten pollen per cubic meter of air were sufficient to trigger an allergic attack.
Ragweed: blooms from July to October
The plants can grow up to about two meters tall, but most specimens are less than one meter high. Their flowering period is from July to October. This prolongs the pollen season. Total pollen concentration.
This can mean a longer period of suffering during the year for allergy sufferers. "In private gardens it is found mainly under bird feeders", explains the Julius Kuhn Institute. This is because birdseed can be contaminated with ragweed seeds.
Ragweed grows mainly along roadsides or at construction sites
After initial surveys between 2006 and 2017, experts had again examined the stocks in Hesse last year. The result: Despite some control successes, ragweed is still present in almost 90 percent of old stands, according to the HLNUG. In addition, a third of the occurrences in some cases show a strong increase.
In addition, nine new large occurrences have been discovered, mostly on construction sites and earth deposits, as well as more than 30 new small occurrences, for example on roadsides. "The species can cope with many sites, but prefers sandy soils, such as those often found in southern Hesse.", explains Kreb.
Legal options for ragweed control are lacking
For Hesse, there is still the possibility to limit the spread of ragweed by consistent action with manageable costs.
"This will prevent long-term allergies and as a result, the health care system can avoid the expected high economic costs." However, the legal possibilities to effectively combat ragweed are currently still lacking.
The Climate Change and Adaptation Center plans to launch a roundtable in the fall of 2022 together with representatives of the state administration and affected municipalities.
The focus will be on how to limit the spread of the plant. Kreb referred to other German states, such as Brandenburg, where entire regions are now colonized by the invasive species, leading in some cases to crop failures. In Bavaria and Brandenburg there are already programs in place to combat the problem.
Ragweed pollen is "highly aggressive"
As far as the threat posed by ragweed is concerned, there are certainly different opinions in science. It has not been proven that their pollen is a particularly strong allergen, says the chairman of the German Pollen Information Service Foundation, Karl-Christian Bergmann, in Berlin.
The allergens were more than 80 percent consistent with its sister plant, mugwort. In the professor's opinion, it is difficult to distinguish exactly which pollen a patient reacts to. Patients with ragweed allergy are extremely rare.
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The assessment of Ludger Klimek, President of the Medical Association of German Allergists in Wiesbaden, is quite different: "We are seeing more and more allergy sufferers suffering from." Particularly endangered are all humans, who already have other breath way allergies. Ragweed pollen is "particularly small and highly aggressive".