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Climate change and "new" allergy triggers extend pollen season

MedUni Vienna Pollen Service: Ragweed and mugwort cause stress
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Bild: MedUni Wien/Bastl
Blühender Ragweed

(Vienna, 29 July 2024) Allergy sufferers in Vienna have to be prepared for pollen release in summer and fall, mainly due to immigrant species such as ragweed and certain types of mugwort as well as climate change. The weed ragweed, which is a major problem for the health and agricultural sectors, begins to flower in August. Since last year, there has also been a second flowering phase of mugwort in September and October. This was reported by MedUni Vienna's Pollen Service Vienna.

The mugwort pollen season in Vienna started in the beginning of July and the flowering period usually lasts from July to September, although the first flowering individuals may appear before July. The widespread pollen release is mainly caused by the local mugwort species, the common mugwort (Artemisia vulgaris).
Mugwort pollen allergy is the most common pollen allergy among weeds in Vienna (ahead of ragweed) and ranks third among pollen allergies. Mugwort is therefore a potent allergenic weed.

Change in the mugwort pollen season
In autumn 2023, Maximilian Bastl from MedUni Vienna's Pollen Service Vienna noticed a striking change: "Suddenly, mugwort pollen concentrations increased in autumn, culminating in a higher peak pollen concentration than in summer. This has never happened before in Vienna."
After scientific research, it became apparent that two neophytic species of mugwort, which had been established in Vienna for some time but had not previously flowered so prominently, were the most plausible causes of this phenomenon: the Kamchatka mugwort (Artemisia verlotiorum) and/or the annual mugwort (Artemisia annua). A neophyte is a plant that has established itself in an area where it was not originally native. These plant species have been deliberately or unintentionally introduced into new regions by human activity and have gained a foothold there.

Which species or whether both species of immigrant mugwort flower to the same extent has not yet been researched. A study from northern Italy (South Tyrol region) has identified these two species as the responsible source in the autumn pollen count there, where the second flowering phase has been around for some time. As there were unusually high temperatures in the fall of 2023 and, according to Geosphere Austria, the warmest September in recorded history in Austria, a second flowering phase of mugwort from September to October can also be expected in Vienna in the future under similar conditions.

Ragweed - an early season and cross-border cooperation
Ragweed (Ambrosia artemisiifolia) has long since established itself here and is also a neophyte. Typical sites include roadsides, highways, building sites and fields. The pollen season lasts from August to October, depending on weather conditions. Earlier flowering is expected this year. This is consistent with reports from one of Austria's neighboring countries, Hungary, which is heavily infested with ragweed. In Vienna, increased ragweed pollen counts must be expected, especially when winds blow from the south-east and east, as the populations are even larger there. The Pollen Service Vienna of MedUni Vienna is a partner of the Hungarian "Ragweed Pollen Alarm System (R-PAS)". The data from MedUni Vienna's pollen trap is made available in return for the use of the Hungarian forecasting model.

Maximilian Bastl from MedUni Vienna's Pollen Service Vienna sums up: "Without neophytic species and climate change, the pollen season in Vienna would already be as good as over, but now people with allergies must expect symptoms in the fall too."