Tips to manage chilli thrips
Rose displays in metropolitan Perth gardens were ruined last summer and autumn due to infestations of chilli thrips (Scirtothrips dorsalis). Perth’s unseasonably humid summer created ideal conditions for this sap-sucking pest to multiply. It gradually moved down from the north of Western Australia, where it was first found about 20 years ago. The destructive pest also occurs throughout the world and has been found on Australia’s east coast in the past.
The larvae cause the most damage while feeding on the sugars in new shoots, but the insects also cause deformities in flowers, leaves and stems due to toxic substances in the pest’s saliva. Adults feed on the underside of leaves. Also known as strawberry and tea thrips, chilli thrips feed on roses, citrus, grapes and other fruit and vegetables. They are tiny insects and are difficult to see without magnification.
Thrips are most active during warmer months and many generations can breed in a single year. They live deep in flowers, or on the undersides of leaves (and on lower leaves or the ground in pre-pupal or pupal stages), so they are hard to control.
Entomologists from Western Australia’s Department of Primary Industries and Regional Development suggest using a multi-pronged strategy to reduce thrips numbers. Hard-prune infested plants to remove damaged plant material, pick up leaves, double-bag cuttings, and place them in the bin. They recommend spraying when new shoots emerge with horticultural oil, horticultural soap spray or an organic insecticide, such as pyrethrum. Spraying in the early morning or early evening is best to avoid harming beneficial insects.
Neem oil is used overseas for organic thrips control but is not registered for this use in Australia. Other trials are underway in Perth rose nurseries to discover which good, predatory bugs reduce numbers. Deryn Thorpe
ABOVE
This is what happened to writer Deryn Thorpe’s roses last summer as chilli thrips descended in large numbers, causing damage to rose buds, stems and leaves.