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There may be environmental reasons. Not a long enough or cold enough dormant period.
If the plant seems healthy otherwise, I would not worry.

Yellow dusting could be pollen that has fallen from flowers. This would be normal and no issue to resolve.

Sometimes Rust fungus could be described as yellow so I'm giving you links with information on how to treat.

https://www.gardeningknowhow.com/plant-problems/disease/learn-about-plant-rust-disease-and-rust-treatment.htm

Spring would be the best time to plant and start seeds.

https://www.gardeningknowhow.com/ornamental/vines/wisteria/grow-wisteria-seeds.htm

I would check for crown or root galls. Here is some information on them that may be helpful: https://www.gardeningknowhow.com/plant-problems/disease/how-to-fix-crown-gall.htm

If that doesn't turn up anything, it may have a fungus. Treat the plant with a fungicide. I like neem oil, as it will also deal with any pest issues the plant has and it is safe for people and pets. Here is more information on it: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm

Roundup probably will kill it either way. However, why don't you dig up the plant, once it is dormant (usually after the first frost) and give it to someone who would like it?

You won't be able to grow the cutting from there but will have to root it if you want to keep that part. This article will help with this: https://www.gardeningknowhow.com/ornamental/vines/wisteria/propagating-wisteria-cuttings.htm