Agriculture: Floriculture and Ornamental Nurseries Pest Management Guidelines

Monitoring with Sticky Traps

Trapping can be an efficient and informative monitoring tool. Traps can alert growers to pests early before crop damage occurs and before pests become abundant and more difficult to control.

Yellow sticky traps

Yellow cards (commonly 3 × 5 inches or larger) covered on both sides with sticky material attract and capture the adults of various flying insects. Yellow sticky traps can indicate localized spots of high pest abundance or periods of migration of adult pests into crops and the predominant direction from which they are arriving (e.g., from an adjacent field of drying weeds). Traps can also provide a relative measure of insect abundance; comparisons of the number of adults caught among sample dates can indicate whether pest density is decreasing, increasing, or remaining about the same over time. Pests captured by yellow sticky traps include adults of fungus gnats, thrips, and whiteflies, aphids, psyllids, and sharpshooters. Others presented side-by-side for comparison in Sticky Trap Monitoring of Insect Pests include leafminers, shore flies, and adults of certain parasites and predators.

Blue sticky traps are sometimes used for thrips because this color is more attractive to thrips. Howeverinsects are more difficult to discern and count in blue traps. Yellow sticky traps attract a wider variety of pest insects and are recommended for most situations.

Sticky traps may not be a good tool for deciding treatment need, whether any action thresholds are exceeded (see ESTABLISHING ACTION THRESHOLDS), and they are generally not effective for direct control. Immature stages feeding on crops commonly cause the most damage; sticky traps typically capture only airborne adults, which in many species do not feed on plants. Adult trapping sometimes is not a reliable indicator of pest presence or abundance on the crop. Many of the trapped adults may be migrating species that don't feed on the crops being grown. Adults often cannot readily be discriminated to species; for example, the adults can obviously be aphids but whether they are aphid species that infest the crops present may not be discernable from specimens stuck in sticky material. Always use traps in combination with visual inspection of plants for the presence of damage and pest feeding stages.

Unless other guidelines are recommended use at least one sticky trap per 10,000 sq. ft. of growing area. When monitoring whiteflies, use about one trap per 1,000 sq. ft. of growing area with crops susceptible to infestation. Actual trap density will be dictated by the growing area and the time and effort devoted to trapping. But each pest management unit should have at least one, well-maintained, yellow sticky trap. In addition, put one trap inside growing areas by doors and vents to detect pests migrating in. Also put at least one trap in each crop that is very susceptible to damage by pests and do not locate the most pest-susceptible crops near doors. Use bright yellow traps, each 3 × 5 inches or larger and covered with sticky material.

Orienting traps horizontally (facing the soil or upwards) is sometimes recommended when monitoring pests such as fungus gnats and shore flies that emerge from or rest upon growing media. However, to catch a wider range of targeted insects, orient the longest part of the trap vertically (up and down). Place each trap so that its bottom is even with the top of the plant canopy. For rapidly growing crops, locate trap bottoms a few inches above the canopy so that the plants do not soon overgrow the traps. As plants grow, move each trap up so that its bottom remains about even with the top of the canopy or somewhat higher. For example use one or two clothespins to attach each trap to a bamboo post or wooden dowel embedded in the growing media or a stand. Alternatively hang traps from rafters or wires strung between posts.

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 film and take them to a more comfortable location for counting. Alternatively replace traps when they become too fouled to effectively capture insects or count them quickly. If traps are reused, note this because catches become cumulative; you must subtract the number of insects present the last time that particular trap was checked, or sum and average the counts from all traps in a specific growing area then subtract the previous average from that currently.

Count and record the number of each type of pest caught. When abundant it is not necessary to count all insects on the entire trap; counting the insects in a vertical column 1 inch wide on both sides of the trap, then multiplying the results by the trap width in inches, gives results that are representative of the entire trap. Do not reduce traps to 1 inch vertical strips because smaller traps will be less attractive to insects. Waterless hand cleaner can be useful for removing the sticky material from hands.

Because many insects in traps may be beneficial or harmless, carefully identify insects before taking management actions. High-quality color photographs and line drawings of commonly trapped insects are available in Sticky Trap Monitoring of Insect Pests. You can also wrap used traps in clear plastic and take those containing unknown insects to offices of the UC ANR Cooperative Extension or county agricultural commissioner for help in identification.

Interpreting Information from Yellow Sticky Traps

Regularly summarize trap data to facilitate comparison. For example, graph the average numbers of each pest in all traps from a particular growing area on each sample date. This allows visual recognition of trends in pest abundance and facilitates comparison to stages of crop growth and when particular management actions were taken.

Interpreting trap information requires knowledge, skill, and practice. Traps catch both migrating insects as well as adults that emerged from the crop. Canopy density, plant foliage quality, and temperature influence adults' tendency to fly. Wind and ventilation fans can discourage flight, reducing trap catches. The number of adults trapped may temporarily drop after a pesticide application even if there has been relatively little change in immature abundance on plants. Conversely, adult numbers of some species may temporarily increase in traps after applying an adulticide, so the numbers caught for several days after an application might not be best when comparing adult densities among sample dates.

Foliage disturbances, such as sprinkling with water (overhead irrigation) or shaking plants to promote pollination or monitor adults (e.g., of whiteflies), increase trap catches. Even large numbers of pest species in traps do not necessarily indicate that control action is needed. Always use traps in combination with plant inspection to determine whether economically damaging numbers of pests and stages susceptible to control actions are present. For more information, see ESTABLISHING ACTION THRESHOLDS.

Sticky Tape Traps

Crawlers, the mobile first instars of certain Sternorrhyncha (formerly Homoptera), are the life stage most susceptible to many pesticides. Traps made of double-sided clear sticky tape (available at stationery stores) are an efficient method of monitoring crawlers of armored scales, foliar-feeding mealybugs, soft scale insects, and certain other arthropods. On each of several plants infested with adult females, snugly wrap a stem with tape. Double over the loose end of the tape several times so you can pull the end to easily unwind it. Place a tag or flag near each tape so you can readily find each tape trap. Change the tapes at regular intervals, about weekly. After removing the old tape, wrap the stem at the same location with fresh tape. Preserve the old sticky tapes by sandwiching each tape unrolled between a sheet of pale-colored or white paper and a sheet of clear plastic. Label the tapes with the collection date, location, and host plant.

Crawlers get stuck on the tapes and appear as yellow or orange specks. Examine the tapes with a hand lens to distinguish the crawlers (which are round or oblong, have very short appendages, and may have two dark eye spots) from contaminants such as dust, pollen, and spider mites. A contact insecticide and certain other pesticide types can be applied when crawlers are abundant. If a single application is planned, visually compare the tapes collected on each sample date. The best time for a single spray is after a sharp increase in crawlers in traps or soon after crawler numbers have peaked and begun to decline.

Text Updated: 03/21