Hello, Our string beans have a silvery film and holes on the leaves. What can...
The foliage of your beans has been subject to feeding by the Mexican bean beetle. In your photo you can see the yellow larvae crawling on the stems of the beans. Larvae and adults feed on the underside of the leaves between the veins which produces a lacy look to the foliage. See our Vegetable Pest Profile for monitoring and prevention/control http://extension.umd.edu/growit/insects/mexican-bean-beetle