Sick potatoes--help! I need disease ID! :(

Hi!
This is my first year growing potatoes.
I planted them May 23, I think, so they are about a month and a half old. I'm in Pennsylvania, if that helps for disease ID.
They started laying down, but I thought that was just natural (aka getting a bit tall for themselves) they still looked super.
They looked happy and healthy and then this morning 2 of them were wilted BAD--obviously dying.
I decided to remove them. Their roots were basically gone. Soggy rot. It HAS been raining a lot. Leaves also yellowed and browned a bit. The healthy ones have a bit of brown, too, not much...Japanese beetles have been chewing  a little.
Please help me identify what's wrong!!
Mostly, I'm worried about my small potato patch spreading a bad disease to my HUGE tomato patch nearby, & eggplants & peppers:0

My "seed potatoes" were a grocery store bag or organic eating potatoes. I realize this could be why they have disease.
Also, I recently (week or 2 ago) heavily hill-ed them with composted manure dirt.

Thanks everybody (in advance!!),
--McKennaugh

To me that looks like root rot, usually from too much moisture for too long a time period.
I don't see any evidence of potato grubs or root maggots.
I expect Kola Lofthouse will chime in and he will have much better knowledge than I.

We grow our potatoes in above ground tubs, mostly for ease of harvesting but if your soil is staying pretty wet, it might be a good way to grow for you too.
We also use a light mix for growing potatoes in that allows for fast exit of excess moisture.

Redhawk

It will be hard to say for sure, given the location and conditions that you describe, to ascribe the problem to one or more disease pathogens.  The clip below was taken from Penn State's website and may hold more information for you:  http://plantpath.psu.edu/research/areas/plant-disease-management-and-adaptive-research/penn-state-potato-research-program

As that website notes, if this is blackleg on your spuds, you may be succumbing to a resurgence of this disease in Pennsylvania in recent years, even though your tuber seed was from unknown origin.  In some regards the leaf symptoms look a bit like late blight, but with the amount of wilt occurring from the root infection, all bets would be off.  At a lost for a remedy...even if you did opt for using a chemical application, you would be pretty limited for this bacterial disease.  You may need to just harvest what you can, make this summer a "diagnostic" experience to learn what you may have to battle down the road, and try to plant (and save seed from) varieties with better resistance to those diseases.  Good luck!

I like growing potatoes in poor soil. Rich soil seems to promote rotting and diseases: especially super-wet rich soil. I'd guess the problem originated as a combination of composted manure dirt and lots of rain. I don't pay much attention to diseases... I can't ID them. I don't have names for them. If a variety doesn't grow well in my garden, with my existing conditions, then I grow different varieties until I find some that work for me.

I agree the roots look rotted. Did you have a soil test done before you planted? If not, I would highly recommend you have an analysis done by a local lab or university before you plant there again. That way you'll have a better idea of what's in the soil which may explain the symptoms of your sick plants. Most soil tests cost about $10-20 and it's well worth it. I do it every year.
If you planted on 5/23 and if the plants grew healthy they probably were not ready to harvest now. I planted my Northland Reds on 4/10 and they're just about ready to be pulled up. Most potatoes need at least 90 days in the ground before harvest.
Also I wouldn't wait to hill them after they lie down. You actually want to prevent them from lying down. Hilling them often or at least when you start to see them leaning toward the ground promotes root growth and therefore larger yields. I've hilled mine about 4 times since I planted. Hope this helps