Answer: Sounds like a bacterial or fungal leaf spot, perhaps brought about by environmental stress. Yellowing leaves can be a sign of iron deficiency, not meaning that there's not enough iron in the soil, but that it's bound up for some reason - perhaps very alkaline conditions. Iron chelate is the form that's most available to plant roots, but your jasmine may need foliar sprays, as well. If it were my plant I'd wait until spring, then prune away the affected plant parts to keep the disease from spreading, and to promote healthy, new growth. Full sun to part shade are the best exposures for jasmine. Water regularly during the growing season and pinch or prune to encourage healthy new shoots. With some extra TLC this spring and summer, your jasmine should regain its health.
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