Scouting Guidelines in Greenhouses

January 29, 2016

Small greenhouses (< 4,000 sq.) can be scouted as one unit. Larger greenhouses should be divided into 2,000 to 3,000 sq. ft. sections for ease of scouting. Scout propagation areas at least every 3 to 4 days. Use your prior experience to determine how many plants and which plants to inspect (those that are most susceptible to pests or diseases in your greenhouse). The more plants or locations inspected, the more likely it is that a problem will be detected in a timely manner, when treatments are the easiest. In practice, scouting is a compromise between thoroughness (examining everything), efficiency (putting limited time to the best use), and cost (the value of improved management information). Sampling a predetermined number of plants in each crop increases the likelihood of locating “hot spots,” which are areas with high arthropod pest populations.

One way is to spend a predetermined amount of time per area of growing space, such as 5 to 10 minutes for each 1,000 square feet of growing area, inspecting 20 or more randomly chosen plants. In addition to randomly selecting plants, be sure to inspect those plants that have always been a problem for you in the past.

Scouting should begin at the major doorway, which is usually an entry point of pests. Special attention should be paid to plants near vents where pests may come in from outdoors.  

Walk every aisle and move from bench to bench in a zigzag pattern. Examine plant parts in a systematic manner.  For example, begin with buds or flowers, then inspect new growth, younger leaves, older leaves and finally basal stems and finally growing media. Examine leaf axils and the tops and undersides of leaves. Many pests prefer the undersides of leaves or inner, protected plant parts. Use a 10- 30x  hand lens to make it easier to see the small arthropod pests. If the plants are small, the sample unit may be an entire plant; for larger plants the sample unit may be a set number of shoots and leaves, such as 2 to 6 per plant. Don’t forget to inspect hanging baskets or any plants on the floor.   The first plant showing symptoms becomes an “indicator plant”. This plant is tagged to allow the scout to easily find it from a distance. Indicator plants can be used to examine the pest’s development cylcle and to monitor the effectiveness of a treatment. Indicator plants should be marked and numbered with a colored flag or flagging tape so the scout can identify them quickly each week.

Indicator plants (petunias or fava beans) are also used to detect the early presence of tosporviruses (Impatiens Necrotic Spot Virus (INSV) and tomato spotted wilt virus) and thrips.

Weeds hidden under benches or behind the furnace are often a source of overwintering insect and mites, so look for and hand-pull those troublesome weeds. Place the weeds in a plastic bag to avoid spreading any weed seeds or insect or mite pests.

For at least several plants in each section, examine roots for root decay, root-feeding insects (root mealybugs or root aphids) or other problems. Follow the same pattern of inspecting each plant every time.  To avoid spreading diseases, wash hands thoroughly or wear disposable gloves and discard them after handling any plants you suspect might be diseased.

Tina Smith, UMass Extension and Leanne Pundt, UConn Extension


Tips on Scouting Spring Ornamental Plants, (UConn Extension)

IPM Scouting and Decision Making (UMass Extension)

Identifying Some Pests and Beneficial Insects on Sticky Cards (UConn Extension)

Integrated Pest Management for Bedding Plants: A Scouting and Pest Management Guide (see section III on scouting), (Cornell University)