The Return of Chilli Thrips

With the onset of spring no doubt chilli thrips will be the main thing on gardener’s minds because it drove people to desperation for months. This year chilli thrips attacked blueberries, grapes, strawberries, chillies, capsicum, hydrangea, asparagus, onion, passionfruit, peaches, mango, and azaleas.

Gardeners basically threw everything they could at them to no avail, systemic insecticides, oils, soap spray, severe pruning and as a last resort removal of the plant. The despair chilli thrips caused most gardeners was on epidemic proportions.

Rob Melville from Melville’s Rose n Garden has shared his experiences with chilli thrips. Their nursery grows thousands of roses, allowing them to trial various control methods, using many sprays available to the home gardener and did a trial plot of hard pruning during summer. The solution they found will probably shock most people its so simple.

Before revealing his team’s solution, it’s important for people to understand the life cycle of Scirtothrips dorsalis (chilli thrips). They have been in WA for around 20 years and are active year-round but more prevalent in spring, summer, and autumn. They are tiny, only 2mm long with a torpedo shaped yellowish  body and wings.

When feeding, chilli thrips use a mandible to cut into the plant, inject their saliva then insert a tube that sucks up semi-digested food. It’s a punch and suck action. In warm temperatures chilli thrips can produce 18 generations in a year and females can lay up to 40 eggs during a lifetime.

Eggs are laid in the foliage and the first two stages of life (instars) occur in the foliage or buds, then they go into the ground or leaf litter for the next two stages of development (prepupa and pupa) finally appearing as a winged adults and continue to feed. The life cycle takes around 15 days. The stages of development in the ground are crucial for control.

Rob Melville found that all the sprays became ineffective after a while as the thrips developed an immunity to them. Sprays including the organic ones were killing any of the predatory insects that fed on the thrips.

He maintains the best method of control was to overhead water daily and not use any pesticides or insecticides. The thrips are so small, during the prepupa and pupa stages they actually drown in the leaf litter. Robs advice is to allow the beneficial insects that predate on thrips to build up, overhead water daily and never hard prune during the warmer months.

Tip

Predatory insects for thrips include pirate bugs, mites, ladybirds, parasitic wasps, predatory thrips, green lacewings, and damsel bugs.