Q.common vinca management
love my vinca, but has become very woody with white stuff on wood and leaves. Can I cut all to the ground level and will it come back nicely in the spring? SW Missouri.

You can do a hard prune on your plants. You can cut them to 4 to 6 inches above soil. Some gardeners actually mow the plant to make this hard prune.
Here are some links to help you.
It sounds like your plant may have Powdery Mildew.
https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
https://www.gardeningknowhow.com/ornamental/groundcover/periwinkle/growing-periwinkle.htm