Garden Pests

Red Spider Mite

The red spider mite is a common sap-feeding pest which causes mottled leaves on greenhouse plants, houseplants as well as garden plants. Common victims are: vines, peach, nectarines, cucumbers, tomatoes, aubergines, peppers, poinsettias, orchids and Impatiens.


These red spider mites love warm, dry conditions, and so will thrive in a greenhouse throughout the year. Outdoor, problems occur in late summer especially when the weather is hot and dry.

Prevention is the best cause of action with these pests, so remain vigilant and spot them earlier as it is much easier to control them before they take hold.


How to spot

Despite their common name they are yellowish-green with a pair of darker markings and are therefore sometimes called the glasshouse two-spotted spider mite. They only become orange-red in the autumn and winter resting period.

The mites are small, up to 1mm (less than 1/16in) long, and are only just visible to the naked eye when found in large numbers.  You may need a magnifying glass to see them. Look on the lower leaf surface and you’ll find their spherical eggs. To see them more clearly you can hold a piece of paper under the plant leaf, shake it and the mites will fall onto the paper.

Heavy infestations are easier to spot, as you will see a fine silk webbing on the plants and leaves lose their green colour, dry up and fall off.


How to treat


These little mites breed very quickly when the conditions are warm. Mist your foliage regularly to create a cool moist environment to help reduce their numbers. However, don’t overdo it as you may have a case of fungal disease on your plants.

Try refined plant oils, such as those derived from rapeseed and sunflower. These work by blocking the breathing pores of small insects and mites, such as aphids, whitefly, and red spider mites.

Also, try Phytoseiulus persimilis – a predatory mite that feeds on the eggs and active stages of red spider mite. It works best when temperatures reach 20°C for a few hours each day. Repeat applications every 2-3 weeks in hot weather. Apply early in the season to keep the pest controlled. Phytoseiulus persimilis can eliminate up to 5 adults or 60 eggs a day.

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