How to recognise it
Rose thrips are cylindrical shaped, brown, sap sucking insects which are 3 to 4mm long. Adults have a pair of narrow wings fringed with hairs, the larvae are wingless and usually lighter in colour than the adults. They can be found on plants from spring to autumn and overwintering in garden debris, wood and brickwork.
The females, which live for about a month, can bear up to 100 eggs in that time, secreting them within young petals and other soft plant tissues. Breeding generally starts in February, but may continue over the winter in warm conditions (eg glasshouses). The eggs hatch, the larvae feed, they become non-feeding pupae and about a week later adults emerge. The adults develop their wings after the pupal stage. The whole process from egg to adult can take only a month in the summer, but much longer in lower temperatures. The adult and immature thrips overwinter in cracks in canes, stakes, brickwork, wood, etc.
Why it’s a problem
Flowers become flecked with light spots and streaks which gradually darken and rot. Leaves may develop silver flecking.
As they are sap feeding, the insects can act as vectors for diseases.
The winged adults may travel long distances on thermal currents, so infestations can easily travel from plant to plant or garden to garden.
Where you are likely to find it
Rose thrips attack roses and other plants, particularly those grown under glass. They are more prevalent in hot, dry conditions (both indoors and outside).
How to deter it
Regular watering and maintaining a cool, humid environment can prevent an infestation taking hold of indoor plants (eg in a glasshouse).
Use sticky traps to monitor thrips levels within glasshouses, blue coloured traps are thought to be most effective at capturing them.
Keeping your rose garden tidy, by removing canes, stakes and other litter, can take away thrips’ overwintering sites. This is particularly important for roses grown in glasshouses where they may continue to breed over winter.
How to get rid of it
If the thrips infestation is severe enough then contact or systemic insecticides can usually deal with it effectively. Ideally select an insecticide which contains bifenthrin, imidacloprid with methiocarb, or thiacloprid. They should be applied as soon as the thrips or symptoms are seen and the application repeated 2 to 3 weeks later if the damage continues.
The predatory mite Amblyseius cucumeris and/or the bug Orius laevigatus can be used as biological controls within glasshouses.
Remove and destroy infested leaves, particularly any with eggs on them.
Is it good for anything?!
Thrips can feed on other garden pests, such as aphids and mites.
Other useful information
Thrips belong to the biological order of Thysanoptera, a name derived from the Greek words for ‘fringe’ and ‘wing’, referring to the fine hairs lining thrips’ wings.
Thrips are also known as thunder flies because they sometimes take to the air in large numbers during thundery weather.
The name ‘thrips’ is both the singular and the plural of the word, you don’t say ‘thrip’ if there’s just one of them (but then, there’s never just one of them!!).