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Controlling Whiteflies on Poinsettias by Paul Pilon

September 14, 2010

The greenhouse whitefly (Trialeurodes vaporariorum) and silverleaf whitefly (Bemisia argentifolii) are commonly observed feeding on poinsettia crops. Whiteflies have piercing, sucking mouth parts and in many instances do not cause detectable injury symptoms to crops. However, when their populations are high, more significant injury is likely and the plants may turn chlorotic and appear mottled from feeding, but these types of symptoms are fairly uncommon.

Although, they do not usually cause visible injury symptoms from feeding, there is virtually zero tolerance for the presence of any adults on crops in today’s marketplace. Due to the low threshold and the ease of controlling them early in the crop cycle, many growers implement preventative programs during production.

Identification

Like their common name suggests, whiteflies are small white flies; adults are typically 1.5 to 2.0 millimeters in length. The silverleaf whitefly is slightly smaller than the greenhouse whitefly, has a slight yellow coloration, and holds its wings roof-like over its abdomen at approximately a 45 degree angle with the leaf surface. The greenhouse whitefly appears nearly all white and holds its wings fairly flat over its abdomen, appearing nearly parallel to the leaf surface. Apart from these most obvious characteristics, it can be difficult to distinguish between the various species and biotypes of whiteflies.

The complete life cycle (from egg to adult) takes an average of 32 days for greenhouse whiteflies and 39 days for silverleaf whiteflies. Females begin laying eggs as early as 1 to 4 days after emerging as adults. Numerous eggs are most commonly observed in a crescent shaped pattern on the undersides of the younger, upper leaves. The spindle-shaped eggs are white at first and turn gray with time. Depending on production temperatures, the eggs of greenhouse whiteflies hatch in about 8 to 10 days and silverleaf whitefly eggs take slightly longer (10 to 12 days) to hatch. Whitefly nymphs are oval and have a pale green to yellow coloration.

The pupal case of the greenhouse whitefly has parallel sides that are perpendicular to the leaf surface, giving the pupa a disk- or cake-shaped appearance; there is also a fringe of wax filaments around the edge of the pupal case. The pupal case of the silverleaf whitefly is yellowish and appears more rounded or dome shaped; the sides are also not parallel and lack filaments along the outer edge. The pupal cases of both whiteflies have several pairs of filaments arising from the top of the pupa.

Their lifecycle progresses through four nymphal stages, a pupal stage, and finally the adult stage, where they may live for one or two months. Each female adult typically lays 200 to 300 eggs in her lifetime. All life stages are most commonly observed on the undersides of plant leaves.

Monitoring

It is recommended that growers scout or monitor poinsettia crops at least once per week to detect the presence of whiteflies (and other pests) and to evaluate the effectiveness of their management strategies. When monitoring, it is useful to use a combination of methods including sticky cards and random plant inspections. For the earliest detection, check the undersides of older, more mature leaves for the presence of all life stages.

Control Strategies

To reduce the occurrence of whiteflies in the production area, it is recommended to start with a clean greenhouse prior to starting a new crop of poinsettias. The production facility should be free of any plant materials including weeds and ‘pet’ plants, which may harbor whiteflies.

If possible, remove all living plant materials from the greenhouse for at least 7 to 10 days between crops- any surviving adults will soon die from starvation. Then growers should prevent the entry of whiteflies into the production area. Inspect all incoming plant materials (such as cuttings, rooted liners, or prefinished materials) for the presence of whitefly immatures and adults before introducing them into the production facility.

Growers can achieve effective control of whiteflies using biological control strategies including the use of the entomopathogenic fungus Beauveria bassiana or releasing parasitic wasps Encarsia formosa for controlling greenhouse whitefly, Eretmocerus californicus and Eretmocerus mundus for controlling the silverleaf whitefly, or the parasitic wasp Eretimocerus eremiccus or predatory mite Amblyseius swirskii can be used for controlling either type of whitefly. Products containing azadirachtin, petroleum oil (horticultural oil), neem oil, pyrethrins can also be used to biologically control whiteflies.

Systemic insecticides containing acetamiprid, clothianidin, dinotefuran, imidacloprid, and thiamethoxam are very effective at controlling whitefly populations, provided they are applied properly. All of these systemic products are in the same chemical class and have a similar mode of action; do not rotate between these products during production. Contact insecticides containing abamectin, acetamiprid, bifenthrin, buprofezin, clothianidin, cyfluthrin, fenpropathrin, flonicamid, pymetrozine, pyriproxyfen, and pyridaben are all effective and can be used to control any hot spots that arise.

Paul Pilon

Perennial Solutions Consulting

paul@perennial-solutions.com

 

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