SHB traps are good, full sun is good. Soil controls (ground drench, nematodes, etc) are questionable. The bees carry the larvae out and drop them in all directions for 100's of feet from the hive, so it makes it pretty prohibitive to cover all the ground that the bees cover with some sort of soil control. The beetles also are capable of flying for miles and home in on hives by detecting alarm pheromone. Recently it has been discovered that they infect the pollen stores with a yeast that generates the same pheromone and allows even more SHB to be attracted. So far, I have found that the combination of hygeinic bees, full sun and traps offers the best control.
"The UNKNOWN, huh? That would be SNORBERT ZANGOX over in Waycross."