Greenhouse - Scouting Poinsettias for Whiteflies

The following are some guidelines for scouting poinsettias for whiteflies.

Scouting your poinsettia houses is critical. Small populations of whiteflies caught early, especially if it is a Q-biotype sweetpotato/silverleaf population, will be much easier to manage than those that get out of hand. Remember that, on average, one female can lay more than 200 eggs in her lifetime and a whitefly population can increase 10 times in 4 weeks!

Some poinsettia whitefly scouting tips and pointers:

1) Smaller houses (less than 4000-6000 ft2) can be scouted as a unit; larger houses should be broken into sections. ?? Inspect, or scout, about 10 plants per 1000 ft2.

2) Scout weekly, and try to scout on the same day each week.

3) To look for whitefly eggs, crawlers (1st instar), nymphs (2nd – 3rd instars), and pupae (4th instar), inspect the undersides of the leaves. Check at least 3 leaves per plant, and make sure to check leaves from different areas of the plant – top, middle, and bottom. 6

Eggs are small and spindle-shaped and are typically laid in circular or crescent-shaped patterns, though they can be scattered across the leaf underside singly or in clusters. You will often see eggs in clusters of white-gray dusty patches. Eggs are small, and magnification is often needed to be able to observe them (a 10-20x handlens is fine).

Nymphs can be seen with the naked eye, though the smallest instars (stages) are often difficult to observe. Nymphs are somewhat oval in shape and lightly colored. Older nymphs will be larger in size.

Pupae are easily observed with the naked eye. Some mistake these for the ‘eggs’. A hand-lens is helpful to determine whether the pupae are greenhouse or sweetpotato/silverleaf whiteflies.

To simplify things, your observations can be recorded as ‘small’ (1st and 2nd instars), ‘medium’ (3rd instars), and ‘large’ (pupae, 4th instars), or for less detail, record all 1st-4th instars as ‘immatures’.

Record any whitefly adults seen when scouting for eggs, nymphs and pupae. Adults can also be monitored with sticky cards or tape. Use 1 trap per 1000 ft2 and place immediately above the canopy, and place extra cards near doors and vents. If this seems too many, set at least a few in the older crops and where whiteflies are most suspected or have been seen.

Avoid, or at least greatly reduce, using sticky cards in greenhouses where you are employing a biocontrol insect; the cards will trap the beneficials as well as the pest. Keep records of what life stages are found and where. This will help in your management decisions and can also provide a history that can be useful in upcoming seasons.

By identifying hot spots, a spot or area treatment can be applied, instead of treating the whole crop and, by knowing the predominant life stages of the whitefly pest, you can adjust your management strategy to optimize control.

Choose an insecticide that is effective for the life stage that is present. Use the information generated by scouting to determine whether or not you are above or below your action threshold (whether it is necessary to apply a treatment to manage the whiteflies).

To avoid the buildup of a whitefly population, the threshold early in the season should be lower than the threshold later in the season. As a guideline, treat when you find above ~ 0.2 immatures per leaf scouted through October. Later in the season, treat when above ~ 2 immatures per leaf scouted. (For the area scouted, calculate the average number of immatures found per leaves inspected). Keep in mind that these are guidelines, and thresholds will vary depending on the practices of each operation as well as the demands of each customer.

Houses that are not thoroughly scouted should consider using higher thresholds. Don’t stop after treatment; scouting after pesticide application is important too! Make sure that your management practices are working.

Reprinted from "Whitefly Watch: Don’t Forget to Scout!" by Nora Catlin, Cornell Cooperative Extension of Suffolk County, NY in the October 2006 edition of the Northeast Floriculture IPM Notes.