Plants no longer auto target nearby enemy champions who haven't been hit by one of Zyra's spells.
"Yeah, we're going to take some power out of Zyra in 7.3. The main change is that her plants won't auto target nearby enemy champions who haven't just been hit by one of Zyra's spells anymore (they currently do so up to 350 range)." - Meddler src.
Deadly Spines (Q) mana cost increased to 70 from 60.