Clematis: wilt or just the result of too much rain?, 0 by picante

picante wrote:
My clematis Ernest Markham gets this every year. It starts at the bottom, and by August it's completely brown. It is not from chemicals. The nursery owner knows quite a lot about plant diseases, and I took him some leaves recently. He told me it is not fungal. He thinks it's a phosphorus deficiency. I've tried high-phosphorus bat guano, Tiger Bloom, a liquid starter fertilizer... all with no results.

Could it be some other deficiency? We have alkaline soil (pH 7.8-8.3) amended with compost. It continues to produce blooms even after it turns completely brown.