Thrips – Identification and Control

Thrips are long, thin insects, usually dark yellow to light brown, measuring up to 2mm long. They have fine horizontal lines on their backs and skinny wings that aren’t great for flying, though they can travel long distances by wind. Thrips feed on the sap of fresh young shoots, buds, and leaves on many garden plants. Their lifecycle lasts about 7 weeks, during which each female can lay up to 70 eggs in slits on leaves. The wingless larvae feed on sap, then drop to the soil to pupate, emerging as adults to start the cycle again.

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Symptoms

• White or cream scorching and discoloration on leaves

• Reduced photosynthesis, which can cause leaves to fall off

• Damage to flowers and fruit

• Leaves may develop a browny, silvery, papery texture

• Small black spots of excrement on leaves

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Control

Keep on top of weeds, as these are common starting points for thrips. If you suspect an infestation but cannot see them, place a white piece of paper under the leaves and shake the plant over it. Using a magnifying glass, you can observe the tiny thrips moving. Sticky traps around the garden are useful for monitoring populations, though only adult flying thrips will be caught.

Remove damaged leaves and place them in a sealed plastic bag for disposal. Insecticidal soap can be sprayed directly onto infected areas, making sure to reach buds and the undersides of leaves. Reapply if adults escape before the spray hits them. As the soap dries, the thrips stick together and die of starvation. Always test a small area first, as some soaps can damage plants.

Lacewings and ladybirds are effective natural predators for thrips and can be purchased online. If using these beneficial insects, do not apply soap afterwards, as it will kill them. In winter, dig soil deeply to bury any overwintering thrips.

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Tip

Avoid spraying during the hottest part of the day to prevent scorching leaves, and try to water in the morning for best results.