If you are trying
to attract the Japanese Beetles, you can hang a trap that uses pheromones but that will have all the neighbor's JBs in your yard near the trap and closer to your plants. I guess if you had a decent amount of Geraniums/Pelargoniums surrounding the trap you maybe could make it work.
If you think about how ants work...they send out scouts to hunt for food, they 'mark' a scent trail and then other ants follow. Japanese Beetles do something pretty similar. At the very beginning of Japanese Beetle season, if you could sit in your garden all day and happen to be looking when the scouting party shows up, you may be able to catch and destroy the scouts before they can mark your plants.
Keep a pail/bucket of soapy water nearby. Pick each JB and drop it into the bucket. Leaves the bucket in place as the aroma of decomposing JBs will deter new beetles from snacking. If you have pets or small children you might add some hardware cloth to keep out the curious. Don't worry about the standing water attracting mosquitoes because the soap in the water takes care of that problem.
If you plan ahead you can apply milky spore which is a bacteria (Bacillus popillae or it is Pacenibacillus popillae?
); it will kill the JBs at the grub stage and the bacterial will multiply in your soil... but (in my opinion) it takes a village...meaning that all your nearby neighbors should agree to apply milky spore at the correct time; over time this will destroy the JBs. The good news is that milky spore is effective for a long time. Initial investment seems high but the result is well worth it.
You could add nematodes to your yard and garden. Steinernema carpocapsae, S. glaseri, S. anomali, Heterorhabditis bacteriophora and others. There are many kinds of nematodes and each works to some extent to destroy soil dwelling stages of JB and other grub thingies. But for the nematodes to work well the garden/yard/lawn needs to be watered regularly (like every day) and nematodes don't work as well if the soil is heavy with clay or extremely sandy. I think maybe scientists can understand how to make the nematode work effectively in the soil - it's all pretty complicated for my old brain. To my way of thinking...if I am gonna stand in the garden and water for 1 - 2 hours each and every day, it would be more effective to just hand pick the beetles and save on the water bill.
You can make a homemade spray using Cedar oil. Eastern Red Cedar/Juniper virginiana if possible. If you buy the Cedar oil it needs to be diluted (sorry, I don't know the ratio yet). I found an article telling that you can buy some Eastern Red Cedar lumber, cut it into manageable pieces and place in a bucket; add hot water and allow to steep like tea for 24-48 hours. Pour the undiluted liquid into a sprayer and spray the Roses or other desirable plants. Too lazy to soak cedar wood or dilute the Cedar oil? There is a ready-to-use product available for purchase in the US and Canada which uses Cedar oil here: http://www.cedarbugfree.com/pr...
Another option is to attract birds to your yard, specifically the type of birds that like to eat Japanese Beetles. I don't have a list for the birds, but maybe make a post over on the 'bird' forum and see which birds like to eat the JBs.