My new cucumber plants that I grew from seed (and even covered with gardening...
My new cucumber plants that I grew from seed (and even covered with gardening cloth) are showing light spots and areas where there is a "thinning" of the leaves. Can you let us know whether it is pest or disease damage and how to act quickly to protect the plants? Thank you.
The cucumber foliage in the photo looks like it was subject to minor sucking insect damage not a disease. At this point no control is necessary.
Continue to monitor the plants. You should be aware of other insect pests such as the cucumber beetle which can spread bacterial wilt. http://extension.umd.edu/growit/insects/cucumber-beetles-spotted-or-striped
and downy mildew, a disease http://extension.umd.edu/learn/downy-mildew-cucurbits-spinach-and-brassicas