Biphenyl — also called diphenyl — is a fungicide that inhibits fungal sporulation, used mainly against surface mould on stored citrus. Residues sometimes persist through the storage period, so maximum residue limits apply and post-harvest treatments must follow good agricultural practice. It is classified by the Environmental Protection Agency as slightly toxic (EPA Toxicity Class III). Treated citrus must be labelled or declared according to market regulations, and packing houses manage application to protect fruit without excessive residues. Its long history illustrates the balance between post-harvest loss prevention and consumer exposure in fresh-produce supply chains.