Sony Discs

Are the Sony discs manufactured by Taiyo Yuden?

I assume you're talking about blanks.

It probably depends on the batch, but the past two spindles of Sony DVD+Rs I've been using were Taiyo Yuden manufactured.

Check the packaging to see if they were made in Japan (not China). If so, it's more likely that they're Taiyo Yuden (though still not guaranteed).

Some of the Japanese Sony DVD recordables are Sony manufactured. They're a great disc anyway, in my opinion as good as Taiyo Yuden, the Taiwanese ones manufactured by Sony are supposedly reasonably good, but be careful as Sony does outsource to Acer/BenQ. If they're made in Japan you'll get a good disc regardless of the brand.