Indian Hawthorne, whats wrong?

[L124C]

Near San Francisco (some fog, wind and clay soil). Most of the Hawthornes look great, but some look like this (branches withoutht leaves, black spots on leaves). Healthy ones are next to sick ones. Thoughts?

[img][url=https://img6.imageshack.us/I/indianhawthorne.jpg/][img]https://img6.imageshack.us/img6/418/indianhawthorne.th.jpg[/img][/url]
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[bullthistle]

Could be just genetics. It happens, some plants are healthier then others, just like family offspring. Sometimes there are no explainations other then genetics.