There are several species of thrips that can cause damage in glasshouses and gardens.
Gladiolus thrips (Thrips simplex) Mainly affects gladiolus during July to September, but also on freesia, causing white flecks on foliage and flowers. Heavy attacks cause the petals to turn brown and buds fail to open. To prevent overwintering thrips from feeding store corms in a cool frost-free place.
Pea thrips (Kakothrips pisivorus) Found on garden peas during June to August; causes stunted growth with a silvery brown discolouration on the foliage and pods; the latter may remain flat with just a few peas developing at the stalk end.
Privet thrips (Dendrothrips ornatus) The adults are brownish-black with a banded appearance of white and dark markings on their wings. They feed on the leaves of privet and lilac during May to October, resulting in the gradual development of silvery-brown foliage by late summer, and may cause some premature defoliation.
Banded palm thrips (Parthenothrips dracaenae) Occurs all year round on various glasshouse and houseplants, especially those with relatively tough leaves such as Ficus, Dracaena, Citrus, Monstera, Schefflera and palms. A blackish-brown thrips with banded brown and white wings that causes extensive silvering of the leaves.
Western flower thrips (Frankliniella occidentalis) A North American species present in Britain since 1986. Attacks the foliage and/or flowers of many glasshouse plants, especially tomato, cucumber, streptocarpus, African violet, fuchsia, gloxinia, achimenes, pelargonium, cyclamen, chrysanthemum, verbena, Primula obconica and Impatiens. Feeding causes silvering of the leaves, stunted growth, flecking and premature senescence of flowers. When buying houseplants, check the flowers carefully and avoid any showing signs of thrips or pale flecking on the petals.
Onion thrips (Thrips tabaci) Causes a whitish mottling on the leaves of onion and leeks. It also feeds on a wide range of other plants, including carnation, chrysanthemum, begonia, cyclamen, dahlia, tomato and cucumber. It causes silvering of the foliage and on some plants, such as dahlia, feeding at the shoot tips results in severely stunted growth and distorted leaves.
Honeysuckle thrips (Thrips flavus) Found on many garden plants but is most frequently found on honeysuckle during May to October. The foliage becomes extensively silvery-brown, especially on honeysuckles growing in warm sheltered situations, such as against a wall.
Glasshouse thrips (Heliothrips haemorrhoidalis) Occurs in heated glasshouses throughout the year, causing a silvery discolouration of the upper leaf surface of many plants. The foliage is also marked with small brownish spots caused by the thrips' excrement. The adults are blackish-brown with yellowish-brown nymphs. This thrips can also survive out of doors all year round and feed on various garden shrubs, especially Viburnum tinus.