Thank you for the question. It sounds like you had a Japanese beetle problem last year and are wondering how best to control them this year on your raspberries and whether products used would prohibit human consumption of the fruit. The safest way to protect your berries if beetle population isn't overwhelming, is daily handpicking of the beetles and drowning them in a bucket of soapy water. If you routinely have many beetles, you could try covering the bushes with a light mesh to exclude the beetle but allow entrance of sunlight, air circulation, and rain.
There really isn't a "best" stage of control for these insects because the adults are such strong flyers that they can come to your property from miles around. Even if you succeeded in killing every grub and adult in your yard, control would be elusive. I'm sorry that this makes the situation sound hopeless but as long as you have plants the adults like, they will come. If you think you have a Japanese beetle grub infestation, the best time to apply grub killer is in the fall when the larvae are small and before they burrow deep to survive the winter. As the weather warms up, they start to come up to feed on lawn grass roots. An irrigated, lush lawn is ideal for grubs. They grow rapidly and are much harder to kill at this stage. Please read our publication on how to determine whether or not you have a Japanese beetle grub problem: http://www.extension.umn.edu/garden/insects/find/japanese-beetles/
There are many different products on the market that fight Japanese beetles at either the grub or adult stage. Many of the "main stream" items can be found at big box stores, but some of the different ones are probably best purchased on-line. The only way to know if a particular product is safe to use on foods eaten by humans is to read the product label and follow the advice and directions exactly. There are a few Bacillus thuringiensis var. galleriae, products available on-line that might be effective. You can do an internet search for beetleJUS, or beetleGONE! A beneficial nematode, Heterorhabditis bacteriophora, attacks JB grubs. Nematodes are microscopic parasitic roundworms that transport and feed on bacteria. When they find a grub, the nematodes penetrate the larva and inoculate it with bacteria, which quickly multiply within the grub's body. The nematode then feeds on the bacteria. Nematodes need to be applied to soil at night and the soil must be irrigated daily to keep it moist so the nematodes stay alive. Again, look on-line. There are a couple of other effective low impact insecticides that can help protect plants from JB, especially if only small numbers are present; Pyola and Neem oil. You still need to read the label to determine if your berries would be safe to eat. Insecticidal soap, extracts of garlic, hot pepper, or orange peels are not effective. Read more about the different products here:
Thank you for contacting Extension. Let's hope we don't have bumper crop of beetles this year!