Spider Mites

This is being caused by a spider mites. These tiny spiders (can only be seen with a magnifying lens) suck plant sap and chlorophyll from the leaves, causing the speckled appearance we see on these leaves. You may also see some very fine, disorganized, webbing with mites in the web. If you confirm, you can use insecticidal soaps or horticulture oils to control them, but don’t over-use these products because you’ll probably be killing other beneficial mites that are natural enemies of these mite pests. When many of the predatory/natural enemies are killed, the spider mite pest population can sky rocket and get worse. You can also help keep the population of pest mites down by occasionally washing off the leaves of the affected plants early in the morning (and allowing them to dry throughout the day). Here are a couple of web-links with more info:
http://www.ipm.ucdavis.edu/QT/spidermitescard.html
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7405.html