Rust spots are usually not life-threatening for a plant. However, if too many of a plant’s leaves become affected and go untreated, the plant may lose too many leaves to continue growing healthily. It is a good idea not to cut off more than 1/3 of a plant’s leaves at a time. If more than 1/3 of a plant’s leaves are affected, it may therefore be difficult to bring the plant back to health, and it may need to be disposed of.