I initially planted 7 tomato plants in May. One plant started off well, but now the upper leaves are coming in deformed. I had a plant last year close to that corner of the garden, but not exactly in that spot that had similar symptoms and it ended up looking so sickly, I just pulled it out. This plant, is a Purple Brandywine, and is actually quite lush and growing well with the exception of the upper sections. The closest images I can find online is herbicide damage or cucumber mosaic virus, both of which seem unlikely to me. Any ideas?