I have a couple of pounds of the food grade Diatomacious earth and I plan to use it on these guys this summer. Have you actually used it?
It kills all bugs and worms without mercy. I love the stuff.
He got it at Lowe's, comes in a good-size box. He used a mask and latex gloves because he didn't want to breathe it, wet down the plant (hisbiscus) with probably a fine spray on a hose (would do it on an overcast day) and just tossed the stuff on the plant, said it lasted for about a week then have to reapply but worth it if it works, better and safer than powerful chemicals.
They had come back from vacation, and there were 15 on his hisbiscus which is right across the fence from my pussy willow; those are preferred plants of the beetle among many others. A week later the count was only 3 which is pretty good considering I don't know if I'd treated my pussy willow with Sevin or not.
I'd need to use a lot more than he did so I'd try to find an applicator that will dispense dust but maybe try it first. You might want to do a little more research on it.
If those stink bugs like soybeans, that is a concern to me. I know the beetles like corn and get in the silk but that's usually self-pollinated before they ermerge; planting has been late this year though. Jap beetles emerge from the ground as adults and the larvae like to feed on grass roots, then burrow way down for the winter. You might have some luck with predator birds eating the larvae, think that's why I've seen so many brown woodpeckers around that had never been here before so don't chase them off. Starlings also like them as do turkeys and ducks.
I'm going to get some netting, too, the kind you use for party and bridal clothes and cover some plants won't look so nice but I don't care, got some baby raspberry plants I started from seed.
The biggest worry is have we reached critical mass? I'm told so far they haven't been that much of a problem with crops, but then nothing aggressive is being done to eradicate them around here.
You can bet if they get in the grape, almond and fruit crops in CA which they like, they will have to pull out all the stops. With the stink bugs, I did like the idea of finding the young and killing them. When I pick, I drown them in soapy water but came to be an exercise in futility and exhausting.
One more thing I did which may have helped some is treat my lawn with oh can't think of the name of it, got it at Home Depot in a big bag and used a spreader, best time to do that is between July 15 and Aug 15 and needs to be watered in. I got lucky and got a good rain, actually applied some when it was raining a bit. Wish I could remember the name, I just did, Grub X.
Whatever you try, good luck. I'm so fed up with these things,ruins my summer. I don't mind bugs generally but these things have come to creep me out. Just a few people try to get rid of them any way they can, but it takes a community effort. They got so bad downtown, they sprayed, and my daughter said there were hundreds of dead ones lying around, probably attracted by trees. They do treat the golf course and rose garden; nurseries don't have too much of a problem because they generally have to fly in because they can't gestate under asphalt.
I'm trying to share everything I've found out about them. Killing them is better than repellants (with the earth is) but anything that works is worth it. The damn beetles get up in my birch trees, start at the top, no way I can spray those; so far they just do damage but some places will get so bad they will defoliate a whole tree. They're a real problem with lindens.
Please ping me if there are any new developments. Massive outbreaks will get people's attention; the fact that the stink bugs feed on the actual fruit is not good.
Whatever you do, don't use Bayer products where the active ingredient is imidacloprid, the same stuff in Advantage for pets for fleas. That is residual on flower blooms and kills bees and wasps, and I partly but not totally blame that for the destruction of honeybees. There was a good article in the LAT about that class of chemicals called Bzzzzzzz Kill, then went into suspect products. They got in the grape crops in France, and settled a lawsuit with France over it, conducting more studies in Germany (where those products are mfr'ed).