Managing Thrips in Vegetable and Ornamental Crops

Thrips (Order: Thysanoptera) are tiny, slender insects (1–2 mm) that cause silvery scarring on leaves, distorted growth, and — critically — transmit the devastating Tomato Spotted Wilt Virus (TSWV) and Iris Yellow Spot Virus (IYSV). Western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci) are the most economically important species.

Identification

Adult thrips are barely visible to the naked eye. Use a hand lens to examine:

• •Growing tips and flower petals
• •Leaf undersides along the midrib
• •Inside curled leaves

Damage signs:

• •Silver-grey streaking on leaves and flower petals
• •Brown scarring on pods, fruit, and bulbs
• •Distorted or stunted growing points
• •Ring spots or necrotic lesions (TSWV symptoms)

Scouting

For flowers and vegetables: trap thrips on blue sticky cards (2 per 1000 m² for greenhouse; 1 per hectare for field crops). Inspect 10 plants per scouting point, pulling apart growing tips.

Threshold: 1–2 thrips per growing tip or significant virus symptoms.

Chemical Control

Thrips are cryptic pests — effective control requires products with systemic or translaminar activity.

Application Tips

• •Treat at first sign of thrips or on transplanting
• •Rotate products every 2–3 applications to manage resistance
• •Apply in early morning when thrips are most active
• •Use fine droplet nozzles (150–250 μm VMD) for good coverage of growing tips
• •Repeat application at 5–7 day intervals during high-pressure periods

Resistance Management

Thrips resistance to spinosyns and neonicotinoids is documented globally. Rotate IRAC groups strictly and avoid unnecessary applications.