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Since May I regularly harvest the leaves and shoot tips of my lemon balm in the herb bed. Cut into strips, I sprinkle the cabbage with the fresh citrus flavor in salads or put the shoot tips as an edible decoration on desserts like panna cotta with strawberries or ice cream. A refreshing treat on hot days is also enriched with lemon juice and a few balm stalks enriched mineral water.
The further the summer progresses, the more unfortunately the lower leaves of my lemon balm unfortunately show unsightly, dark leaf spots. After consultation with a specialist in plant protection, this is a leaf spot disease caused by the fungus Septoria melissae. In nurseries that grow these plants, this mushroom is even considered the most important harmful factor and can lead to massive yield and quality losses.
Damage of Septoria melissae to Zirona melissa
This is how to recognize the fungal disease
First, there are several dark, well-defined spots on the lower leaves, which quickly spread over the whole plant in humid weather. On the upper leaves, however, usually only small dark spots are visible. As the infestation progresses, the lower leaves may even turn yellow and die off. Spores that the fungus propagates in the plant tissue are spread by moisture such as dew or raindrops. Close together plants and a moist and cool weather favor the development and distribution of Septoria melissae.
Ms. Ed. Beate Leufen-Bohlsen
As a countermeasure, the expert advises me to consistently cut off the diseased leaves and to make sure that the plants are only watered from below. So that the leaves can dry off faster, I plant the aromatic herb in autumn to a loftier place.
Part of the stems will now be cut back just a few centimeters above the ground as part of summer care. The lemon balm then willingly replaces fresh stems and leaves.