Grass-type Pokémon are weak to several types of attacks, including:

• Flying-type: Grass-type Pokémon are weak against Flying-type attacks.
• Poison-type: Grass-type Pokémon are weak against Poison-type attacks.
• Bug-type: Grass-type Pokémon are weak against Bug-type attacks.
• Fire-type: Grass-type Pokémon are weak against Fire-type attacks.
• Ice-type: Grass-type Pokémon are weak against Ice-type attacks.

On the other hand, Grass-type attacks are strong against Water-, Rock-, and Ground-type Pokémon.