How to: Properly monitor with sticky traps

Adult whiteflies, thrips, fungus gnats, leafminers, psyllids, shore flies, winged aphids and parasites can be monitored with yellow sticky traps. Traps provide a relative measure of insect density; comparisons of the number of adults caught among sample dates may indicate whether pest density is changing or remaining relatively constant over the long term. Traps often alert growers to pests early, before damage is observed in crops. Traps must be used in combination with visual inspection of plants.

Use bright yellow traps, each 3 by 5 inches or larger. Consider using blue sticky traps for Western flower thrips. Use at least one sticky trap per 10,000 square feet of growing area. When monitoring whiteflies, use about one trap per 1,000 square feet. If growing under cover, place one trap by vents and by doors to detect populations migrating in.

Orient the longest part of the trap vertically (up and down). Place each trap so that the bottom of the trap is even with the top of the plant canopy. For rapidly growing crops, locate the trap’s bottom a few inches above the canopy so that the plants don’t overgrow the traps. As plants grow, move each trap up so that its bottom remains about even with the top of the canopy. Alternatively, hang traps from rafters or wires strung between posts. Traps may be placed horizontally (facing the soil) when monitoring pests such as fungus gnats emerging from media.

Number each trap and map its location in your growing area. Inspect each trap at least once or twice weekly. It is easiest to replace traps each time you inspect them. Wrap traps in clear plastic and take them to a more comfortable location for counting.

Count the number of each type of pest caught and keep a record of these data. It is not necessary to count all insects on the entire trap; counting the insects in a vertical, 1-inch-wide column on both sides of the trap will give results that are representative of the entire trap. Do not reduce traps to 1-inch vertical strips, as smaller traps may be less attractive to insects.

Because many insects in traps may be harmless or beneficial, carefully identify insects before taking action. Ask a cooperative extension or county agricultural department expert for help with identification.

Source: University of California IPM program