Sure. Now probably would not be a good time since all the JB grubs that existed in your soil are now the adults that are flying around plus others from your neighbors. 'round about the first of August you can apply the milky spore disease and about the middle of August put the parasitic nematodes down, but you need to look closely at your soil to find out why your plants attract these buggers. Plants grown in a good, healthy soil are not bothered by pests and diseases.

It would be more effective if you apply nematodes and the spores in the lawn area, and use the remaining for the flower beds. The turf grass is where many more grubs concentrate to feed on roots. Nematodes and spores will need to travel down the mulch layer before the grubs can be infected. My preference is to remove the mulch to apply them, and then put the mulch back. But this is not practical in many ways. The spores and nematodes that you apply at the lawn area near the flower beds will eventually move (under ground) into the flower beds to give the protection as well.

"Plants grown in a good, healthy soil are not bothered by pests and diseases."

That's not true. Japanese Beetles actually PREFER healthy roses.