If you have a magnifying glass try looking for spider mites or eggs on the underside of the leaves. Spidermites will also spin webs so look for that, might not be cobwebs. I'm not really sure if that's what that is, but it's worth looking for. Might be a nute deficiency by the way the veins of the leaves are turning white. Spider mights are attracted to the chlorophyll , green stuff. Keep an eye out and good luck, they look pretty, 7 leaf-er