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Red spider mite, also known as two spotted spider mite, is a very common sap-feeding mite that can be found on many different plant species indoors and outside. They are around 1mm in length, yellowish-green in colour with two dark green spots on their backs and active throughout the warmer months. During the cooler months with shorter day lengths, the mites change to a red colour and become dormant, congregating within protected locations such as cracks in brickwork, the middle of bamboo canes and under dry leaf material. In spring, they emerge from their resting period and the females begin laying small spherical eggs across the undersides of newly developing leaves. This will continue through the summer months and as the population becomes larger, infested plants become covered in fine webbing and their leaves begin to die.
Initially the leaves become mottled where spider mites are feeding. This increases as the infestation builds up. Leaves can become completely necrotic and die. Plants become increasingly more covered in fine webs. Heavily infested plants will eventually wilt and die.
Where spider mites have been present the growing areas need to be thoroughly cleaned during the cooler months. Old canes and pots should be soaked in an appropriate cleaning agent or destroyed.
Due to the speed at which red spider mites breed, it is often difficult to completely control. Heavily infested plants and leaves should be removed and destroyed if possible. If using biological control, the predatory mite Phytoseiulus persimilis will predate on red spider mites and can be obtained from commercial suppliers. As a last resort, organic products containing fatty acids or plant oils/extracts are also available from garden suppliers. Always ensure that the label instructions are adhered to.
Regular spraying of plants with water and watering around the base will also help to reduce infestations as red spider mites do not like high humidity.