Those yellow traps can be effective if a large number are deployed over several acres. A couple years ago, I put 15 traps out over 5 acres and put a dent in the
local beetle population. Milky spore can be effective at killing the beetles that come out of your ground, but does little to stop the beetles that emerge from your neighbor's property and fly onto yours.
Chickens also have a good reputation of killing the beetles.
Switching over from biological control to chemical/physical control, Neem oil and Chrysanthemum based pesticides (PyGanic, etc) supposedly knocks down the beetle population while Kaolin clay (Surround WP) may make the leaves irritating
enough so the beetles move on to other trees/plants. Four O'clocks allegedly attract the beetles and are slightly toxic to them. This year I am trying out a combination of PyGanic and Surround WP, but the preliminary results have not been particularly encouraging.