Now I'm trying to plant stuff in these beds and I'm finding big, fat, c-shaped, white grubs everywhere I dig. Even little 6-inch holes have at least 2 grubs each! They are so Disgusting!

I know we had bad japanese beetles problem earlier, but the backyard was mostly void of grass (new yard). Except for these prepared beds, the backyard consisted mostly of assorted weeds and bare soil.

So here are my questions:
1. what did these grubs in the beds eat to get so disgustingly fat? I thought they eat grass roots, which we didn't have much of a few months ago? And what are they doing in my beds? I thought they were only a lawn menace?

2. Will they chomp up the roots of my newly planted babies? Will they migrate to the newly grown grass and decimate those?

3. What should I do now? I did notice a few grubs in July and sprinkle some sevin on those beds then, but not the lawn, since there was no lawn to speak of then. Guess that didn't work ...

Thanks very much for any advice you can offer!

Are you seeing any plant damage? Lots of times a population of grubs isn't something to be concerned about as not every population is going to harm plants or turn into something bad.

However, if damage occurs or you just want to proactively get rid of them the Sevin should work. Read the instructions though as the effectiveness of most grub control products is dependant upon timing of the application. A lot of the products have to be applied before the adult lays the eggs. A BT strain which paratisizes the grubs is a good choice as well, but often the soil has to be warm (70F) at application time. So, you will have to read up on your options and choose accordingly. Your county extension service probably can suggest what will work well for you as many products that have been shown very effective in one area did poorly in a another. Soil chemistry varies widely from one place to the next which is a likely reason for the differing performance so a call to the extension office or a chat with a master gardener in your area is probably your best source of info for this.

That said, the adults -- large green clumbsy flyers -- feed on *over-ripe* tomatoes and tree fruits.

link is to gov't info on japanese beetles, which answers most of your questions, and has photos including one of the grub (larva).

I have found milky spore to be of the most help, but it does take a while to be effective (about 2 years). And you will probably always be fighting JBs since they will travel to get food. But there is a difference between spending fifteen minutes hand-picking the all critters in your garden and seeing more beetles than leaf (which is what happens when you don't try any controls).

"... During the feeding period, females intermittently leave plants, burrow about 3 inches into the ground--usually into turf--and lay a few eggs. ..."

Also
"... In early spring, the grubs return to the turf and continue to feed on roots until late spring, when they change into pupae...."

Beyond that, grubs are *next to impossible* to ID from a photo on the web, or even in a book. Particularly when info re size, and distribution of the hairs on its butt, are lacking.

We forum folks are long-distance guessers when it comes to IDing one of these confusing insects -- among them grubs.

In such instances, in order to obtain a confirmed ID, one may need to take a sample to a local expert, among these are a University Extension Office, a county or state agricultural commission/department/agency, and/or a large independent garden center or farm store.

"the female wasp digs into the soil, paralyzes a beetle grub by stinging, and then deposits an egg on the grub. When the egg hatches, the emerging wasp larva consumes the grub."

Go girl, chomp away! Now, that's my kind of wasp :) The BT and nematodes sounds promising too. I'll look into their availability here.

But it's a relief to know that I don't have to be out there spraying stuff just because I've got grubs. The plants all seems to be doing fine right now, but I'll start thinking about grub control for next year. Thanks very much everyone for your input!

Their eggs are laid in turf. The grubs (youngsters ) eat the roots of turf. They're not interested in mulched beds.

I doubt you have any reason for concern. When you find them, stomp them, or cut them in half, or feed to birds, or something else. And have fun with your new garden bed!