THRIPS ON VIBURNUMS and other plants
Viburnums, especially winter-blooming
V. tinus, are often seen with silvery brown leaves (above), particularly on the lower parts of the plant. This damage is caused by small sap-sucking pests called thrips. Look under the silvered leaves and you’ll most likely see telltale blobs of excrement that resemble black dots. It’s harder to see the pests themselves, as the adults are usually only 1–2mm long.
Thrips are tiny, sneaky insects that hide under leaves or within flowers and suck out their goodness. Often they aren’t noticed until their damage has appeared. There are close to 1000 known species of thrips in Australia. Many are goodies that control other pests such as mites, but some are particularly troublesome, such as the plague thrips that infest and spoil blooms in spring. Plague thrips (yes, they come in plague proportions) love light-coloured flowers, and often interfere with pollination. It’s difficult to control plague thrips, and sometimes it’s best just to wait until they move on as the weather warms.
To prevent thrips, keep plants well fed, spray water through the leaves regularly (thrips don’t like being wet), and treat severe attacks with organic insecticidal soap. Be aware, though, that discoloured leaves will never go back to green. Prune off damaged foliage in spring if possible, and fertilise to promote new growth that will cover up the damaged sections.
Thrips are often found attacking indoor and glasshouse plants. Some other plants that are commonly targeted by thrips are gladioli and the native snake vine (Hibbertia scandens). Monitor your plants regularly and be ready to take action as problems begin. Some people recommend laying reflective foil around the plants – apparently the reflection deters the flying adult thrips – but this isn’t a practical solution in most gardens.