In a commercial vineyard with a vine that was planted last year? Yes. In a home garden, it depends. You will definitely get more vigorous growth if you cut back. But that particular cane in your photo looks almost thick enough to leave. How tall of a trunk are you trying to get? If it were mine, I would keep it and not prune back to two buds but keep only 4-5 well-positioned shoots near the top. In the vineyards I manage, if the vine was planted last year, we cut it to two buds in the spring regardless of vigor, but we need uniformity in our vines that a home grower doesn’t.
If you cut to two buds and the resulting shoot has enough vigor to reach the height you want your trunk early enough in the season, you can top it and start training out the shoots that will become your horizontals the same year.
Theoretically, any bud on 1-year-old wood can fruit, so a vine like yours is capable of producing. Any fruit you leave will be at the expense of vegetative growth, but on a vigorous plant, a cluster or two won’t hurt.
I totally agree, thank you @GrapeNut for the guidance. @zone7a seems like we’re in a similar position! Only I think I’ll actually trimming mine, since their pretty thin.
The top of the trellis is in full sun and at the base is quite shaded. Do you think the thinness is because of low light or is it just because the roots were brand new last year?
I only have 2 vines so a little extra maintenance isn’t a big deal for me, but it sounds like your expert opinion is to go ahead and cut and re-grow from 2 or 3 buds this year, so I’m planning on taking a deep breath and going for it!
Shade could cause the shoots to stretch a bit, but it being their first year of growth was probably the biggest factor.
If you decide to cut back, make sure the new shoots are protected from anything that will want to eat them. Slugs and rabbits are the biggest problems for us in young plantings. Once the shoots grow, let them get about a foot to 18 inches tall, tie them to a stake, then remove the extras. It’s important to tie first then remove, because in tying, sometime you can accidentally break off the shoot you want to keep. This way you have a back-up or two.