Answer: It is not only unwise, but illegal, to use any pesticides in a manner contrary to what is on the label. Do not use pesticides labeled for use on lawns on edible crops!
There are other ways to address your problems. Japanese beetles are a difficult pest to control. Your best bet is a two-prong approach: one to deal with the larvae, one to deal with the adults. Japanese beetle grubs are best controlled by spraying beneficial nematodes on the lawn and garden area. These microscopic worm-like creatures attack only the grubs in the soil and not plants, animals or humans. Spray them in spring when the temperatures are above 55F and you should see a difference that summer. For adult beetles, I'd try a new product called whole neem oil. This is different than the Bioneem in that it is a stronger concentration of this organic spray.
I would avoid using those Japanese beetle traps. In some cases, it appears that they actually draw beetles to them from the surrounding area--and you don't need to be attracting extra beetles!
As far as your root crops, it's important to identify the culprit. If the onions are have tiny holes, it's most likely the onion maggot, the larva of a small, black fly. The adult fly overwinters on crop debris and emerges in spring to lay white eggs on young onion plants near the soil line. The white larvae burrow into the base of the onion, causing it to rot. Onion maggots like soils high in organic matter and cool, damp conditions. Avoid applying manure, compost or even mulch in spring. Wait until the weather gets above 60_F to topdress with compost and apply mulches. If using manure, apply it in the fall and till it in right away. Fall tilling also buries the overwintering pupae. Applying diatomaceous earth around the onion transplants can be effective, although you must reapply it after rain. Row covers placed tightly over an onion bed can prevent flies from getting to the plants, but in a badly infested area, onion flies can emerge, mate and lay eggs all under the cover so check periodically.
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