Guignardia advice?

[MDBuch]

Katrina, they’re growing about four feet from a west-facing window.

Would that mean I’d need to cut this off wherever I’m seeing it? I’ve got eight plants by this window, and I’ve found small patches of it on a significant portion of the plants, probably around 40% of the leaves there have some kind of spotting. Not nearly as bad as those pictured, just a few spots, but they’re there nonetheless.

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Thanks Ray. Are there smaller quantities available? Should I just go through the Southern California rep? Is it only available for online order, or can I find it in any local nurseries?