I noticed that fields of grape vines were covered with green plastic near Bakersfield, CA. Why?

To protect them from wet weather, you know how much rain we've had lately, and the grapes will mildew.(Arvin, Ca. resident myself)

Plastic Vines

It could be because they were anticipating rain at a time when the grapes could split because of too much moisture. Wine grapes can be especially damaged by too much or to little moisture.

Maybe to prevent them form bird pecks? When I worked on an orchard we put netting over the rows of grapes because the birds did so much damage to them when they tried to eat them.