Try using indicator plants to check if whitefly populations are being managed. Whitefly host plants include tomato, lantana, gerbera daisy, poinsettia and eggplant.
Whtiefly photo by Guido Bohne

Scouting for greenhouse pests takes skill and time. It’s a critical piece of any integrated pest management program. If your operation is seeing more than average pest pressures in any given growing season, make sure your scouting techniques are polished and crews get the proper training.

Scouting begins before a crop enters the greenhouse. One month prior to the introduction of a crop, evaluate the entire greenhouse. Look at weeds in and around the greenhouse, drainage problems, algae build-up, pet plants, overwintered plants and debris under benches. Crops growing in adjacent greenhouses or outdoors should be recorded.

Prevention of key pest problems is more easily accomplished if the grower and scout take the time to identify, analyze and correct as many problems contributing to pest problems before crops are introduced. Keeping seedlings separate from cuttings in propagation houses and vegetable transplants separate from ornamentals helps reduce the incidence of tospoviruses (impatiens necrotic spot virus or tomato spotted wilt virus) when western flower thrips are present. When a crop arrives, scouts should inspect one-third or more of the plants.

Sticky cards

Sticky cards should be in your IPM toolbox for pest detection. Blue cards may be more attractive to thrips (and even shore flies), but it’s more difficult to see thrips against the blue background. Yellow sticky cards are used to detect infestations of adult flying insects in greenhouses. Attach each card to a stake with a clothes pin. Another option is to glue two clothespins back-to-back. Attach one end of the clothespin to a stake and clip the card to the other clothespin. This will allow you to move the card upward as the plant matures. For general monitoring, attach sticky cards vertically just above the plant canopy. For fungus gnats, place cards horizontally just above the soil surface or lay them flat on rims of pots. Aphids and thrips tend to be caught on the bottom half of the traps. Leafminers are caught more often along the top, and leafminer wasps and whiteflies tend to be spread uniformly over the trap. Aphids tend to be caught in the middle vertical columns. Since insects are not distributed evenly horizontally across the trap, columns counted should be vertical towards the middle of the trap.

Each yellow sticky card should be numbered and placed in the greenhouse at the minimum rate of one card per 1,000 square feet. Space the cards equally throughout the entire range in a grid pattern. Place cards near all entryways and vents. Small greenhouses (less than 4,000 square feet) can be scouted as one unit. Larger greenhouses should be divided into 2,000- to 3,000-square-foot sections. Change the cards weekly and place new cards in the same areas of the greenhouse to track pest trends.

Scouts should keep detailed records of pests detected, the counts, and any unusual circumstances found in the greenhouse. Pictured: aphids on Ipomoea.
Sticky cards are an important tool in an integrated pest management program.
Scouting takes skill. Make sure your staff is trained properly.
Aphid photo by Ohio State University; sticky card and scouting photos by University of Vermont

Monitoring and keeping records

Monitors should walk every aisle and move from bench to bench in a snake-like or zig-zag pattern.

Begin inspections at the bottom of the plant and proceed upward, from older leaves to younger leaves to new growth. Special attention should be paid to buds and blooms. Pots should be tipped sideways for inspection of the underside of the leaves where many pests reside. Root examinations should be performed on crops that are highly susceptible to root disease by inverting and removing the pot. Don’t neglect to inspect hanging baskets.

Identify and record pest numbers in a notebook. Compile weekly summaries and itemize information for each greenhouse according to the pests detected, the counts and any unusual circumstances found in the greenhouse.

Detailed records of any pesticide application should be kept to compare with previous records to see if fewer applications have been made or if a less toxic chemical has been substituted. These records should include the following information:

  1. Date of spray application
  2. Name, classification, amount of active ingredient, and registration number
  3. Amount of material and water mixed for the application
  4. How much of the pesticide was applied
  5. Where the pesticide was applied
  6. Square feet or number of pots treated
  7. Type of application method (wet spray, fog, etc.)
  8. Applicator’s name
  9. Labor hours
  10. Over time, population trends will emerge and provide direction for your pest management program

Indicator plants

Indicator plants may also be used to check if treatments were effective. A highly susceptible host plant is an excellent indicator plant. Grown among the commercial crop, it is the first plant to become infested and helps simplify crop monitoring. Indicator plants should be marked and numbered with a colored flag or flagging tape so that the scout can identify them quickly each week.

Some highly susceptible host plants and the pests they attract are:

  1. Whiteflies – tomato, lantana, gerbera daisy, poinsettia and eggplant.
  2. Spider mites – marigolds and roses.
  3. Aphids – sweet peppers and fuschias.
  4. Thrips – petunias and impatiens.

Sources: University of Massachusetts Extension; University of Connecticut Extension (; Oklahoma State University Cooperative Extension, Mike Schnelle and Eric Rebek, ( Consult and follow pesticide labels for registered uses. If any information is inconsistent with the label, follow the label. UConn Extension does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. UConn Extension, UMass Extension and OSU Extension are not endorsing any product or company.