Red spot disease
So gehst du gegen die Rotfleckenkrankheit vor
Several reddish spots spread on the leaves of strawberries, usually the affected leaf parts are or turn yellow.
Treatment
To contain the fungal infestation, remove the affected leaves at an early stage. Red spot often occurs together with white spot disease. This causes the reddish spots to turn whitish. The spread can also be reduced by spraying horsetail tea on several consecutive days.
Rasbak, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons