These tiny, sap-sucking pests may be only 0.5mm long but they can wreak havoc in a greenhouse or on houseplants indoors. For most of the year they are a pale green colour with two dark spots on their back; it’s only in autumn and winter that they turn orange-red. They thrive in hot, dry conditions so life in the greenhouse, or a centrally-heated home, suits them just fine. If the temperature stays above 12 celsius, they can breed all year round.
Leaves and stems of plants covered in fine webbing. The upper surface of the leaf is mottled, while mites and eggs can be seen with a magnifying glass on the undersides of leaves. The plant may die.
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Improve air circulation in the greenhouse and boost levels of humidity by misting plants with tepid water and standing bowls of water on the benches between plants. Damping down the floor of the greenhouse with water will also help. When daytime temperatures in the greenhouse hover steadily around 21 celsius, you can try releasing the predatory mite, Phytoseiulus persimilis on to your plants. Alternatively, use sprays containing, fatty acids or plant oils.