Yellow sticky cards are widely used in scouting/monitoring programs to attract and capture the adult life stage of greenhouse insect pests including fungus gnats, leafminers, shore flies, western flower thrips and whiteflies. Yellow sticky cards (3 x 5 inches) will also capture other insects within the greenhouse such as adult aphids, moths and beetles.
Proper sticky card use
Yellow sticky cards provide information on insect pest population changes or trends, and presence or absence throughout the growing season, which helps to approximate the timing of insecticide applications. However, the use of yellow sticky cards has limitations and is really not a sufficient means of assessing the efficacy of insecticides.
Yellow sticky cards should primarily be used to determine presence and absence, and assess the population of adult insect pests both in space and time because yellow sticky cards do not take into consideration the egg, larval and pupal populations. Nonetheless, the use of yellow sticky cards may be the most cost-effective and least time-consuming method to determine the number of insect pests compared to destructive sampling, which is not practical for greenhouse producers.
Sticky card placement
Yellow sticky cards, for most insect pests, should be placed just above the crop canopy (Fig. 1) and set by attaching the yellow sticky card to a bamboo stake with a clothespin so that the yellow sticky card position can be adjusted as the crop increases in height (Fig. 2 and 3). However, for fungus gnat adults, yellow sticky cards should be placed horizontally near the growing medium surface because adults are most active in this region of the plant canopy.
In addition, yellow sticky cards can be placed on the rims of flats or containers (Fig. 4). One side of the yellow sticky card can be used during the first week by leaving the protective wax paper on the unused side of the yellow sticky card for use during the second week. This allows for one yellow sticky card to be used for two weeks.
Yellow sticky cards should also be placed near greenhouse openings such as doors, vents and sidewalls in order to detect the migration of adult winged insect pests from outside the greenhouse. Furthermore, yellow sticky cards should be positioned among the crop near openings including doors and vents, which will detect adult aphids, leafminers, western flower thrips and whiteflies dispersing inside greenhouses from weeds, field and/or vegetable crops located nearby. In addition, yellow sticky cards should be positioned underneath benches in greenhouses with gravel or soil-based flooring (Fig. 5) so as to detect the presence of adult fungus gnats, shore flies and western flower thrips. This will help determine if these insect pests are pupating in the soil or gravel underneath benches.
However, if pest numbers are low due to seasonality, or when fewer crops are being grown in the greenhouse, then yellow sticky cards can be changed less often. Scout at least once per week and record the number of insects captured on the yellow sticky cards onto a data sheet. The number of yellow sticky cards to place within a crop varies depending on the greenhouse operation and crops grown. However, in general, one to two yellow sticky cards should be used per 500 to 1,000 square feet, although more yellow sticky cards can be used if crops are susceptible to any of the viruses transmitted by the western flower thrips, like Impatiens necrotic spot and Tomato spotted wilt virus.
Finally, the effectiveness of a scouting program is contingent on being able to identify the insects that are captured on yellow sticky cards. At right are images of the adult stages of insect pests on yellow sticky cards including western flower thrips (brown insects in Fig. 6; Fig. 7), whiteflies (Fig. 8), fungus gnats (Fig. 9 and 10), shore flies (Fig. 11), and leafminers (Fig. 12).