Which sticky trap colour works for which pest?

Colour matters because different insects are attracted to different wavelengths. Yellow sticky traps catch whitefly, aphids, jassids, leaf miner adults and winged forms of many sucking pests. Blue sticky traps mainly catch thrips. So in a chilli or onion crop where thrips is the worry, use blue, and in cotton or vegetables troubled by whitefly use yellow, or put up both. A common guide is around 8 to 10 small traps per acre for monitoring how bad the pest is, and more, sometimes 20 or more per acre, if you want to actually trap and reduce numbers. Fix them just above the canopy and raise them as the crop grows. Remember sticky traps are a monitoring and support tool, they will not by themselves clear a heavy infestation, but they tell you early when pests arrive so you can act in time. Replace or re grease them when the surface fills with dust and insects. Check trap numbers for your crop with the local KVK.