The only trouble with Curse is his coverage, far too many things are 4x resist or immune to Grass, Poison and Ground, or a combination of. That and he's still susceptible to Burn, which is everywhere, and not a bad idea since he's immune to Toxic and Leech Seed anyway. It's why I enjoy mixed Growth sets more which are harder to wall. Get a turn in Sun somewhere to get +2 in both and you get mixed Edgequake coverage with Earthquake and HP Rock. PEtal Blizzard is more accurate than Power Whip and has better PP, so its a far safer option.