How To Deal With Thrips in Your Irish Garden
What is Thrips?
Thrips (singular: thrip) are tiny, slender insects about 1-2mm long that feed on the flowers, leaves and fruit of a wide range of garden plants. Also known as thunderflies or thunderbugs, they are often noticed in large numbers on warm, thundery summer days when they fly in swarms. Several species affect Irish gardens, with the western flower thrip, onion thrip and pea thrip being the most damaging. Thrips feed by rasping the plant surface and sucking up the released cell contents, causing a distinctive silvery or bleached appearance on affected tissue. They are particularly problematic in greenhouses and polytunnels where warm conditions allow rapid reproduction.
Damage Caused by Thrips
Thrips cause a distinctive silvery or white mottling on leaves and flowers where they have rasped away the surface cells. Flower petals develop pale flecks and streaks, with dark green or brown spots of thrip droppings. Onion thrips cause white patches on onion foliage. Pea thrips distort pea pods and beans. Gladiolus thrips cause brown streaking on flowers and silvery leaf damage. In greenhouses, western flower thrips damage tomatoes, peppers, cucumbers and ornamental plants, and can transmit plant viruses.
How to Prevent Thrips
Hang blue sticky traps in greenhouses to monitor and catch thrips — they are more attracted to blue than yellow. Maintain adequate ventilation in greenhouses and avoid hot, dry conditions that favour thrip reproduction. Inspect new plants before bringing them into the greenhouse. Remove plant debris that could harbour thrip pupae. Mulch around garden plants to make it harder for thrip pupae in the soil to emerge as adults.
How to Treat Thrips
Spray with organic insecticidal soap or neem oil, ensuring thorough coverage of flowers, shoot tips and leaf undersides. In greenhouses, introduce predatory mites (Amblyseius cucumeris) or predatory bugs (Orius) as biological controls. Blue sticky traps reduce adult populations. For outdoor thrips on onions and peas, spraying is usually impractical and cultural controls are preferred. Accept that some minor thrip damage on outdoor flowers is inevitable in warm summers.
Thrips in Ireland
Thrips are common in Irish gardens during summer, with populations peaking in warm, dry weather. The outdoor climate in Ireland generally limits thrip damage compared to warmer countries, but greenhouses and polytunnels provide ideal conditions for rapid reproduction. Onion thrips can be problematic in Irish vegetable gardens during dry summers. Western flower thrips has become established in Irish commercial glasshouses and is occasionally found in domestic greenhouses. The swarming behaviour of thunderflies during warm, humid weather before thunderstorms is a familiar summer phenomenon across Ireland.
Plants Affected by Thrips
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