Shown here is a problem I have with leaves on all my plants since a few days. This picture shows the problem at a stage when I can first detect it. It will get worse within a few days. Please also note the next two pictures of the same problem at later stages. The problem first appeared on one of the older leaves but now spreads to younger ones, too. Is it a lack of water, a fungal or bacterial disease or something else? Any ideas are welcome! We had some really cold and wet weather from planting time until about the end of May but then we got several days around 90°F with no rain at all. I thought the ground was still wet and so I didn't water really much. But the plants never showed any signs of drought like drooping or wilting leaves, etc.