Brown rot may refer to:
- Ralstonia solanacearum - is a plant pathogenic soil bacterium. It colonises the xylem, causing a bacterial wilt in a very wide range of potential host plants. It is known as "bacterial wilt", "southern bacterial wilt" and "Granville wilt" when it occurs in tobacco
- Colletotrichum coccodes - is a fungal blemish of potatoes and tomato roots that are often only just visible to the naked eye. It is known as brown rot on the fruit of tomatoes, aubergine and pepper.