Cure Plant cures a diseased Farming patch. However, it will not revive a patch that has already died from disease. It is only really effective with an earth staff or a lot of earth runes as a simple plant cure potion only costs 25 coins from a nearby farmer.
When a player attempts to use Cure Plant on a healthy patch, they are given with the message, It is growing just fine. If the patch is fully grown, players are shown the message, That's not diseased. If the player casts the spell on a compost bin, the message, Bins don't often get diseased. appears. Attempting to cast the spell on a patch with weeds triggers the message, The weeds are healthy enough already. Casting it on an empty patch generates, There's nothing there to cure.
Also, when a player attempts to use this spell on a dead plant, they are greeted with the message, It says 'Cure' not 'Resurrect'. Although death may arise from disease, it is not in itself a disease and hence cannot be cured. So there.
If the player casts the spell on any other object, such as trees, rocks, etc., the player exclaims in the chat box, Umm... this spell won't cure that!