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Pests aren’t usually too much of a problem on outdoor crops, but in greenhouses commons pests include aphids, glasshouse whitefly and red spider mite (properly known as two-spotted spider mite). Commercial growers use biological control agents to manage these pests and these are available to gardeners: where to buy. Soft soap is useful for reducing the numbers of pests – use distilled, rain or soft tap water to dilute it. You can also use yellow sticky traps.
There is more guidance here: Pesticides for Home Gardeners RHS Advisory Service February 2015
Did You Know?
2.5 million native British Bumblebees (Bombus terrestris ssp. audax) pollinate all the tomato crops in the UK. That’s 24 billion wing beats per minute in British tomato greenhouses.