INSECT AND MITE MANAGEMENT
ON POINSETTIAS

Introduction

Poinsettia growers can potentially deal with the following pest groups:

1. Whiteflies (two primary species, silverleaf and greenhouse, plus occasional visits from the bandedwinged whitefly)
2. Mealybugs (citrus mealybug, but perhaps others)
3. Thrips (western flower thrips, plus others)
4. Fungus gnats
5. Caterpillars (e.g. leafrollers)
6. Mites (including the Lewis and two spotted spider mites)

Despite this list of possible pests, most producers will deal with two main pest groups: fungus gnats (usually early) and whiteflies (throughout the crop). A good pest management program will focus on the most likely problems but will not ignore the other possibilities. The approach to pest management on poinsettias is no different than on any other crop, and includes basic things such as pest detection and identification, biological knowledge, record-keeping, plus using available physical, cultural, chemical and biological management methods.

General Pest Management

Because the poinsettia crop is already well underway for 1998, it is too late to discuss some of the preventive methods that can be used, such as greenhouse sanitation, weed control, etc. however, it is not too late for pest monitoring. Yellow sticky traps will capture whiteflies, fungus gnats and thrips. Blue traps are often used when thrips are the major insect problems, but this is not likely to be the case with poinsettias. Use sticky traps at a minimum rate of 1 trap per 1000 square feet. Place additional traps near doorways, vents, and under benches. I feel that sticky traps are best used to determine how a pest management program is going, not to detect the insects before beginning a program. Plant inspection (i.e. scouting) is the best way to detect all pest groups.

Fungus Gnats

Fungus gnats can stunt or even kill poinsettias. They normally appear during propagation or shortly after potting rooted cuttings, so by now you would know if there was a problem with fungus gnats. Many poinsettia producers use a preventative approach to fungus gnat control, and do not wait until adults are caught on sticky traps or larvae are seen on potato pieces to begin a control program.

Control is usually directed at larvae, which damage plants directly. Chemical controls are applied as drenches or "sprenches". A sprench is something between a full soil drench (e.g. when liquid runs out of the container) and a normal spray. One or two applications are usually made. Registered conventional insecticides are DuraGuard and Knox Out GH. There also are a number of insect growth regulators used, including Adept, Azatin, Citation, Distance, Pyrigro, Precision and Enstar II. Remember that insect growth regulators do not kill adult insects and activity will be slow. Gnatrol, a Bacillus thuringiensis product, is another "soft" alternative for fungus gnat control.

There are excellent options for biological control of fungus gnats. Predatory mites, Hypoaspis miles, are being successfully used for fungus gnat control on greenhouse vegetables and ornamentals. Beneficial (insect-attacking) Steinernema feltiae nematodes are available for fungus gnat control, and are being applied successfully. Nematodes are applied as drenches to the potting media.

Whiteflies

The main whitefly control program used by most poinsettia growers is applying imidacloprid (Marathon). Other conventional pesticides and insect growth regulators should be used before and after Marathon applications. Control of both the silverleaf and greenhouse whiteflies with Marathon has generally been excellent, if the pesticide is used correctly. Correct use means not to apply the product too soon, before roots are available to take up the chemical, and not to use too much water, so that the active ingredient is washed out of the container. Application timing is less precise, but seems to be best when the roots reach the edges of the container (about now). You should be using other products for whitefly control before and after Marathon application, such as a pyrethroid insecticide + Orthene, one of the insect growth regulators (e.g. Azatin, Adept, Precision/Preclude, or Enstar II), Beauveria bassiana (BotaniGard, Naturalis-O), oil or soap. On mature crops, the best choice seems to be smoke generator applications of sulfotepp (Dithio, Plantfume 103).

Mealybugs

Citrus mealybugs, Planococcus citri can be problems on poinsettias. About the only way that mealybugs appear on poinsettias is for the insects to move onto the plants from elsewhere in the greenhouse. The best way to prevent this from happening is to produce poinsettias far away from mealybug-infested plants.

Thrips

Some thrips species, (e.g. Ecinothrips americanus) can develop on poinsettias. However, this species does not seem to be very common in most greenhouses. Our major thrips species, the western flower thrips, does not develop on poinsettias but can cause injury by distorting leaves, generally early in the crop. This seems to occur mostly in greenhouses where thrips were problems before the poinsettias were moved in. A good thrips control program on other crops in the greenhouse, and particularly on the crop that precedes the poinsettias, will help minimize injury.

Spider Mites