Wait until leaves and vine die back. They need to rest for 10 to 21 days while starch converts to sugar (makes them sweet), don’t wash them until ready to eat. Always be gentle with them, they have very thin skins.

Yes I’m a Master Gardener.

Thank you, @Tropical_Willie.
So, I suppose that the yams won’t be ready for harvest until late fall, as the plants are still growing quite vigorously right now. Right?
I don’t know how deep the roots go. Is it better to use a shovel or a hand trowel to dig them up?

Use a digging fork put fork into ground about a foot away from leftover vine. Pull handle toward you and lift once the soil is loose.

OK, thanks!