While feeding, the beetles carrying the bacterium infect the plant. The disease quickly spreads throughout the plant, blocking water, causing the plant to wilt.
Other cucumber beetles are attracted to the infected plants and continue to vector the disease to healthy plants.
There is nothing you can do once the plant is infected with the bacterium. Remove and dispose of the plants.
You can prevent the damage from occurring by preventing the beetles from feeding.
Row covers are effective for excluding the beetles in the early part of the season. However, the covers need to be removed in order for bees to pollinate; row covers are not the best method at this point.
Sprays are most effective now but will need to be applied on a regular basis during this period of heavy feeding. This can mean spraying every two weeks during peak activity (which is in the beginning stages right now in my area of northern Clark County).
The beetles are pretty good hiders and might be hard to find. However, their damage is very visible on the leaf surface; tiny holes that turn brown around the outside edges are easy to see.
If you suspect cucumber beetles and can’t find them, take a piece of paper and place under the vine. Knock on the leaves gently and chances are you will knock them onto the paper.
I found mine the other night by knocking them off the plant and onto my black fabric mulch.
Use a garden insecticide that is labeled for vegetables and says it controls cucumber beetles. These products would contain permethrin, esfenvalerate or carbaryl.
If you have had a history with these beetles on your garden plants, next spring start early in the season at planting time using row covers. Remove for pollination and then switch to sprays.