How do I make my own sticky traps cheaply at home?

A homemade sticky trap is just a bright coloured surface coated with something sticky. Take yellow or blue plastic sheets, painted tins, old yellow oil cans or even yellow plastic folders. Coat them with a sticky layer, castor oil, grease, or a mix of castor oil with a little petroleum jelly so it does not run off in heat. Tie or staple them to a stick and place them just above the crop. The colour does the attracting, the sticky layer does the catching. They cost almost nothing and work well for monitoring whitefly and aphids on yellow, thrips on blue. The downsides are that the home coating dries or runs in strong sun and dust sticks fast, so you must re coat every week or two. For a small farm this is a very practical money saver. If you want longer lasting traps the ready made ones hold their stickiness longer.