Pest sampling is crucial to understanding the exact pest population in the greenhouse.

Indirect sampling can include yellow sticky traps, pheromone traps, and blacklight traps. Bethke recommends at least one sticky trap per every 10,000 square feet. One trap per every 1,000 square feet is best. Position the traps vertically above the crop.

“One trap per 1,000 square feet is recommended when a serious pest problem exists or the crop is sensitive to pests,” Bethke explained. “This more expensive but is much more effective at catching a serious problem in the greenhouse.”

Traps do not provide data on immature pest populations and disease, Bethke says. Insects are attracted to the color yellow and are drawn to the yellow traps. Insects are attracted to plants since green plants contain a heavy yellow pigment.

Direct pest sampling is the most precise way to determine actual pest thresholds. Bethke recommends examining plant or leaf samples, turning the leaf over for inspection since insects tend to hide on the back side, and observational counting by walking down the plant row.

Direct sampling should include optivisor or a hand lens to examine the leaf for pests. Bethke recommends further examination under a microscope. Positive pest identification is the key to proper pesticide control and determines if pests have been killed by the treatment applications.

Other effective direct sampling techniques include tapping the plant to knock insects onto a sheet of white paper for examination. On large trees, hitting the limbs can knock off pests for gathering.

With both plant sampling methods, Bethke recommends scouting the entire area in a consistent, uniform manner - inspecting several plants from various locations. Target pest hot spots near vents, doors, edges, warmer areas, and more susceptible plant cultivars. Then flag the hot spots.

Treating the entire structure with pesticide may not be necessary.

“It doesn’t make sense to treat the entire facility if the pests are only at a corner of the greenhouse or near a door,” Bethke said. “Treating only the hot spots saves time plus pesticide and labor costs.”

Written records should include the number of plants inspected, damage or infestation, specific pest species and abundance, exact pest locations, environmental conditions, the time involved to scout and apply control measures, and control costs.

Pest monitoring has many benefits including: precise pest site locations, evaluation of control measures, collecting data over time which helps predict future pest populations, reduced pesticide resistance, lower pesticide exposure to workers, improved plant growth, and increased profit by reducing pesticide costs.