Central European forests are under increasing pressure. Diseases such as ash dieback and Dutch elm disease, as well as mass outbreaks of bark beetles favored by climate change, are causing considerable damage in deciduous and mixed forests. Longer dry periods, heat, and repeated years of stress further weaken the vitality of many tree species.
Against this backdrop, new, complementary approaches to forest protection are coming into focus – especially those that do not rely solely on control or felling, but on strengthening the natural regenerative capacity of trees.
Ash dieback in Germany: a widespread challenge
Ash dieback (ADB), caused by the fungus Hymenoscyphus fraxineus, is one of the most serious tree diseases of recent decades. In Bavaria, as in other regions of Germany, almost all ash stands are now affected. Healthy, symptom-free ash trees have become an exception in many places.
Typical symptoms of ash dieback include dying shoots, crown thinning, and the formation of so-called secondary shoots inside the crown. In advanced stages, the trees increasingly lose stability and vitality, making them susceptible to further damaging factors.
Forestry experts point out that classic measures – such as the premature removal of damaged trees – reduce safety risks but do not offer a sustainable perspective for the preservation of ash as a tree species. Against the backdrop of climate change, complementary solutions are therefore increasingly being sought.
Practical trial at the Strogen near Salmannskirchen
Against this backdrop, a small practical trial was carried out in the area of the Strogen stream near Salmannskirchen/Tal. The aim was to test whether a biological treatment could positively influence the vitality of trees already affected by ash dieback.
For this purpose, four ash trees clearly affected by ash dieback were selected. Each of these ash trees received a one-time application of approx. 40 liters of watering water, enriched with a 3-per-mille addition of the biological plant stimulator Karrikin (bamboo distillate) from deNatura. The application took place close to the ground in the root area.
Visible changes were observed relatively shortly after the treatment:
- Increase in leaf mass
- stronger foliage
- increased chlorophyll content
- overall more vital crown structure
The treated ash trees are clearly visible in the accompanying photographs. A few dead branches are still visible, dating from before the treatment and documenting the previous course of the disease.
Further treated ash trees near Wifling
In addition, other ash trees affected by ash dieback were treated in a forest section near Wifling. The forest area belongs to Rainer Mehringer, chairman and managing director of the Waldbesitzervereinigung Erding (WBV Erding).
These ash trees also showed a significantly improved condition after the treatment. Today, the trees present themselves with dense foliage and a vital overall impression, without pronounced symptoms of active ash dieback.
Expert classification of the assessment
On October 29, 2025, the treated ash trees in the forest school of the Waldbesitzervereinigung Erding were assessed on site. The assessment was carried out by Peter Kellner, representative of the Waldbesitzervereinigung Erding w. V.
At the time of the assessment, the marked ash trees showed a predominantly vital condition. The crowns were fully foliated, and the shoots were developed up to the outermost bud. In the majority of the trees examined, no typical signs of active ash dieback could be detected.
The initial uncertainty as to whether all the ash trees assessed had actually been affected by ash dieback about 1.5 years ago was clarified retrospectively. Rainer Mehringer, chairman and managing director of the Waldbesitzervereinigung Erding and owner of the forest school, confirmed that all marked trees showed corresponding symptoms before treatment.
Peter Kellner summarizes his observations as follows:
"My managing director Rainer Mehringer confirmed that about 1.5 years ago, all marked ash trees were affected by ash dieback. During the assessment on October 29, 2025, I could not detect any signs of active ash dieback on any of the treated ash trees. Against this background, the conclusion is obvious that the treatment with Karrikin significantly contributed to the regeneration of the trees."
– Peter Kellner, Waldbesitzervereinigung Erding w. V.
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