Experts warn of a further spread of the heat-loving ragweed plant.

"It is increasingly becoming a health problem," says Aljoscha Kreß from the Center for Climate Change and Adaptation at the Hessian State Agency for Nature Conservation, Environment and Geology in Wiesbaden.

The pollen of the ragweed could trigger serious respiratory allergies and even asthma in sensitized people.

Originally, the Ambrosia artemisiifolia (mugwort ragweed), that is the scientific name, comes from North America.

She is "a new citizen with a particular health risk," reports the Julius Kühn Institute, a federal research institution.

"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 are sufficient to trigger an allergic attack.

Ragweed control

Plants can grow up to two meters tall, but most are only half that height.

They bloom from July to October.

This extends the pollen flight season and concentration.

This can mean a longer period of suffering for allergy sufferers.

"In private gardens, they are mainly found under bird feeders," explains the Julius Kühn Institute.

This is because birdseed can be contaminated with ragweed seeds.

After the first surveys between 2006 and 2017, experts in Hesse again examined the stocks in 2021.

The result: Despite successes in combating ragweed, almost 90 percent of the old stocks are still present, with a third showing a strong increase in some cases.

In addition, nine new large deposits were discovered, mostly on construction sites and earth deposits, as well as more than 30 new small deposits, for example on roadsides.

"The species gets along with many locations, but prefers sandy soils, which are often found in southern Hesse," explains Kreß.

Hesse still has the chance to limit the spread of ragweed with manageable costs.

“In this way, long-term allergies can be avoided and the healthcare system can avoid high economic costs.” However, the legal options were still lacking

split opinions

The Center for Climate Change and Adaptation therefore wants to set up a round table with the state and local authorities in the autumn.

The aim is to limit the spread of the plant.

Kreß referred to other federal states such as Brandenburg, where entire regions are populated by the invasive species.

In Bavaria and Brandenburg there are already programs to combat it.

As far as the threat from ragweed is concerned, there are also other opinions in science.

It has not been proven that the pollen is a particularly strong allergen, says the chairman of the German Pollen Information Service Foundation, Karl-Christian Bergmann.

The allergens corresponded to a good 80 percent with the sister plant mugwort.

It is difficult to distinguish which pollen a patient is reacting to.

Patients with ragweed allergy are extremely rare.

The assessment of the President of the Medical Association of German Allergists, Ludger Klimek, in Wiesbaden is quite different: "We are seeing more and more allergy sufferers." People with other respiratory allergies are particularly at risk.

Ragweed pollen is "particularly small and highly aggressive".