Citrus rust mite attack the outer exposed surface of the fruit. Fruit blemish occurs from infestation of huge numbers of mites on green, immature fruit in summer/autumn. Symptoms of citrus rust mite are a slightly rough, greyish-brown blemish with outside edges turning a deeper brown. The blemish shows up prominently when the fruit colours and becomes more severe the longer the fruit remains on the tree. Rust mites can also cause bronzing of leaves and green twigs.