Cashew production in Tanzania has declined dramatically since the mid‐1970s. Changes in socioeconomic factors have Influenced this, but previous work has shown that cashew tree yields have been substantially reduced by the occurrence of powdery mildew caused byOidium anacardii.This disease was first recorded from Africa in 1979 and is an apparently new introduction. Most of the cashew tree population in Tanzania appears to be susceptible to the disease, which has its most severe effect on the inflorescence and prevents fruit set. Characteristics of the cashew powdery mildew pathosystem are reviewed, and control strategies based on the use of fungicides and host plant resistance are discussed.