I really like druid idea of casting their own weapons, so I have a few suggestions
First of, at early levels (even lvl 1) all druids, either normal druid or blightcaster, should be able to conjure a wooden quarterstaff to beat up opponents. Any self respecting druid has control over the plants to do that, plus its the most iconic weapon for a druid to have (and the only two handed he gets to master without extra feats).
It doesn't need to have especially powerful enchantments at druids normal form, maybe give it spinters doing some small passive damage to opponent after getting hit or making it an implement. But since its our druids favourite weapon (cause that how I like him ) it will change form if druid is using fire or water elemental (do fire damage or ice damage) and like thornblade schimitar (poison/acid damage) while thorn or hive forms. As for animal forms, not sure, add a doublestrike and strikethrough chance or something. Obviously the quarterstaff gets improved as the caster grows, like schimitars do.
Second is thorn knight. The cool word for me here is Knight, so my suggestion is that our druid, while he is in that form (and only in that form, not even thorn kin), should be able to conjure not only a schimitar or 2 schimitars but also a schimitar and a shield. The shield should be wooden and maybe have some acidy/poisonous spikes on it to do some acid/poion damage with shield bash or any other shield attacks. Maybe giving him shield bashing too, but thats not necessary, if one wants to use thorn knight with shield they would already make sure to get the appropriate feats.
Third is hive master. Since in that form our druid is half normal, half a swarm he should get passivly the effects of feather fall and extra boost on jumping, you know to make him fly a bit. Or give him an action boost similar to the memory of flight (with differet name)
P.S.: I think thornblade is a bit too bright green, sure i get its because its acid and poison, but its a wooden weapon, just tone it down or make it woody with bright green edge.