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How to monitor for greenhouse pests

A 5-minute video demonstration of all the right ways to set up and monitor for pest and disease issues in the greenhouse.

September 21, 2020  By Cara McCreary, Dr. Sarah Jandricic, Ashley Summerfield, and Dr. Rose Buitenhuis

Weekly monitoring of greenhouse crops is essential for the success of integrated pest management programs. This includes both pest incidence and severity. In this video, greenhouse researchers and extension specialists will demonstrate key steps and how to best carry them out for effective monitoring.

Set up yellow monitoring cards

The first step in a scouting program is setting up small sticky monitoring cards to detect flying insect pests, including thrips, white flies, winged aphids and fungus gnats.

Depending on the size of your greenhouse, use a minimum of one monitoring card per 100 to 200 square meters. Sticky cards should ideally be changed every two to four weeks to ensure accurate insect counts and maintain stickiness, depending on pest pressure.


Good record keeping of card counts is important, including the numbers of pests and flying beneficials caught on the cards, corresponding plant observations such as damage, and whether counts follow a general trend or indicate a sudden influx of pests.

Inspect plants weekly

When inspecting vegetable crops, scan plants as you move down the row, flip leaves over at random intervals and check the flowers. Gently shake the heads of tomato crops to flush out whitefly. Be sure to inspect the entire stems and roots of unhealthy looking plants.

In ornamental crops, scan the benches as you walk down the aisles. Pick up five to ten percent of the pots on each bench at random and check the underside of leaves, growing points and stems to look for aphids, whitefly, mealybug and disease issues. Remove the pot and look at the roots of any wilted plants to check for disease. Plant taps are a great way to determine thrips pressure per plant.

In addition to insect and mite pests, look for unusual colouring of leaves, stems or roots, wilting foliage, unusual lesions and insect droppings including frass, cast skins or honeydew. When insect and mite pests or suspected diseases are found, mark the plants using different colored flags or flagging tape indicating different pests, then flag the end of the row and record the week number on the flag. This helps you return to problem areas to determine if management strategies are working.

Other useful traps

Pheromone traps are another important monitoring tool. For example, a large yellow sticky trap can be baited with a chemical lure that is attractive to adult pepper weevils. Indicator or trap plants that are particularly attractive to certain pests can also be used to detect pests at low densities. Examples include marigolds or verbena for thrips, eggplant for whitefly and beans for spider mites. These can be used in vegetable or floriculture crops.

Look for trends

Once you’ve recorded observations from card counts, plant inspections and traps, use software to help visualize and track your data. Scouting records help you notice recurring trends in each crop, such as frequent hot spots and seasonal timing of key pests. This data can help you make evidence-based management decisions, which improves plant health and can save you time and money.

For more details and demonstrations of the techniques mentioned, have a look at this 5-minute video.

This is one in a series of videos generously funded by the Canadian Greenhouse Conference, with support from Greenhouse Canada and Flowers Canada. 

Cara McCreary is the greenhouse vegetable IPM specialist, and Dr. Sarah Jandricic is the greenhouse floriculture IPM specialist at the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). Ashley Summerfield is a senior research technician, and Dr. Rose Buitenhuis is the research scientist in biological control at Vineland Research and Innovation Centre.  

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