Sale marks latest step by the German pharmaceutical company to lower debt as it continues to defend legal claims in the U.S.

Bayer has been seeking to lower debt since its big bet on agriculture with its $63 billion acquisition of Monsanto in 2018 turned sour.

BERLIN—Bayer AG agreed to sell its pest-control unit to private-equity firm Cinven for $2.6 billion, as the German chemical and drug giant seeks to focus on its core agricultural portfolio and reduce debt.