Vol. 1, Issue 8 (September 2001)

Special Poinsettia Report

This page brought to you with the co-operation of the Alberta Research Council and Alberta Agriculture, Food & Rural Development

 Whitefly

The whitefly is the most serious insect pest of poinsettias. It sucks sap from leaves and stems causing plants to wilt. There can also be a build-up of honeydew and sooty mold on leaf surfaces. Heavy infestations of whitefly result in plants becoming chlorotic and mottled. The grayish black sooty mold reduces the visual appeal of poinsettia plants. It takes from 20-60 days for greenhouse whitefly to complete its lifecycle, depending on temperature. Females lay up to 120 eggs in its 30-40 day adult lifetime. Whitefly infestations build up very rapidly so you must start your monitoring early. Visually inspect undersides of poinsettia leaves for larvae and pupae. Adults are easily caught on yellow sticky cards. The whiteflies will generally start on stressed plants, which escape grower's attention because they are located away from the main walking areas. Experience dictates that if you have caught one whitefly on a sticky trap, you have several others around which did not "come" to the trap. Although we have not seen sweet potato whiteflies in our greenhouses this year, remember that they may be around yours.

Control: Newly emerged whiteflies are virtually defenceless against insecticide sprays because the integument is still soft and is not covered with wax. On the other hand, eggs and pupae are tricky to control with insecticides. Imidacloprid (Impower 60WP, Merit 60WP) is the greenhouse insecticide of choice for most Canadian poinsettia growers for controlling whiteflies. It is used 10-14 days after the pinch. It is applied once as a drench during the crop season. It is also recommended for aphid control. Although it is highly effective, you may require an additional treatment. DYNO-mite may be used in rotation for controlling whiteflies. These new generation insecticides are absorbed through the roots. It is therefore, important that these insecticides are applied when plants are not under water stress and plants are actively transpiring.

Thrips

It is generally observed that thrips do not prefer poinsettia if the thrips have a choice of different food sources. However, in some situations controlling thrips in poinsettia is necessary especially when the damage occurs on young leaves. Thrips damage on poinsettia is seen as feeding scars or "silvering" in spots and deformed leaves when leaves are older. Thrips damage is easily noticeable when the crop is young. As the crop grows it may be difficult to detect. The thrips problem may be serious when a poinsettia crop follows after bedding plants and the greenhouse has not been cleaned properly between crops.

Control: Monitor for thrips. Trumpet, Decis, and Nicotine are registered for western flower thrips control. Nicotine will control both adults and nymphs. Foliage and blooms must be dry at the time of application. Trumpet provides excellent residual control of thrips. Repeat application is required one week later.

Fungus Gnats

Fungus gnat control is usually critical early in the crop season, preferably before poinsettia plants arrive. You should have at that time treated fungus gnat larvae under benches with labeled insecticides such as Citation, Dimilin or the biological larvicide Vectobac. Citation is effective against all larval stages. If this was done, continue monitoring for fungus gnats. In addition to the yellow sticky traps, potato disks can be used to monitor the larvae. Insert 2-3 cm (1-inch) cubes or disks of peeled raw potato about half inch deep into media. Inspect the underside of each potato and the soil immediately beneath it weekly. The numbers of larvae you find will tell you how successful your earlier control was. Adult fungus gnats are easily controlled with aerosol formulations of insecticides.

This information and earlier issues are also available on the web at: http://www.agric.gov.ab.ca/greenhouse

The mention of a commercial product does not constitute an endorsement or recommendation by Alberta Agriculture, Food & Rural Development or the Alberta Research Council.