Japanese beetles are devouring the leaves of all my plants despite fewer beetle traps and repeat treatments of diazinon on the lawn.
Healthy plants are less likely to suffer from stresses caused by the weather, insects or disease.
Next, stop using diazinon unless you can verify you have a problem with Japanese-beetle grubs. Diazinon also kills beneficial organisms, so spot-treat only these areas with grubs. Milky-spore bacteria offers an organic approach to combating beetles, but if it sits on the shelf too long, the organisms may be dead. It's not a guaranteed control, so I don't like to recommend it. Be careful about using traps, they attract Japanese beetles to your garden before actually trapping them.