We had a few hot days, and the leaves started to turn yellow and curl up. Now entire plants are dying off. It can't just be the heat. I don't see any signs of fungus or pests. We just harvested our first batch for pickling, and I was expecting several more batches, but now I don't know if I'll get them. The plant is still trying to produce runners and there are still flowers, but most of the plants look nearly dead. Any clues?