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Pests: find out more SPIDERMITE
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The Pest
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Glasshouse spider mite or two spotted mite (Tetranychus urticae) is one of the most damaging pests which attack horticultural crops. A wide range of crops are affected, both protected and field grown. Spider mites have a rapid reproduction and development which make resistance to chemicals more likely.
The mites feed by sucking sap from the under surface of the leaf. This produces groups of small white speckles which are clearly seen from the upper surface of the leaf. When mite numbers become high these spots coalesce, giving a bleached appearance to the affected tissue. This can affect both plant appearance and reduce photosynthesis which may in turn result in plant death. Spider mite also produce webs and some strains have toxic saliva which can cause serious damage when only few mites are present (toxicity is most common on tomato plants). |
Spidermite eggs and
larva
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Life Cycle
There are 5 development stages: egg, larva, two nymphal stages and the adult. Fertilised eggs produce females, unfertilised eggs produce males. Spider mite can vary from light green to brown in colour. The duration of the life cycle is very dependent on temperature and varies between 14 and 30 days. At 18ºC it takes 21 days and at 21ºC it takes 15 days. Adult female spider mites hibernate through the winter in the glasshouse structure or in crop debris etc. Hibernation is induced by decreasing day length and/or poor plant condition, and at these latitudes will start in August. Hibernating mites are orange-red in colour and generally hibernate close to where they were feeding; therefore outbreaks in the new crop almost always occur in the same area as in the previous year. Spiders usually emerge when the temperature and day length increase. In heated protected crops mites will appear as soon as the heat is turned on, but damage is often not seen until early January. This can be earlier if the gap between crops is short and the cleanup procedures insufficient.
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Spidermite and webbing
Spidermite adults |
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