Whiteflies are the main insect pests of poinsettias. As most of you know, there are two species that cause nearly all of the problems: greenhouse whiteflies and silverleaf whiteflies. If you produce poinsettias chances are that one or both whitefly species will appear. This is a good time for a reminder of what should be done to effectively and efficiently manage these insects. The following are some things to keep in mind.
Marathon probably will be the main component of an insecticide program for whitefly control. There now are two formulations, Marathon 1% G and a Marathon wettable powder formulation (60 WSP). The powder formulation is registered for application only as a drench. Marathon formulations can be applied only once per crop.
- Irrigate before applying Marathon, so that the chemical can be applied to moist potting mix. This gets the active ingredient into the root zone.
- Do not irrigate heavily for one week after application. Heavy irrigation may leach the active ingredient out of the potting mix before the roots can take it up.
- Apply after the root system has developed but before plant growth slows down. This is about three or four weeks after potting a rooted cutting. Marathon uptake by roots is directly related to plant transpiration.
- Watch for mites. Marathon will not control mites, as many poinsettia growers found out in 1995 and 1996.
- There are many other products that will control whiteflies on poinsettias before Marathon application. During the weeks before Marathon application, use sprays of Orthene + a pyrethroid (Decathlon, Tame, Talstar, Topcide) , Sanmite, insect growth regulators (Precision, Enstar II), or the mycoinsecticides Botanigard or Naturalis-O. All should help keep whiteflies from becoming well-established.
As crops mature, and if whiteflies have re-invaded the crop, use smoke generators containing sulfotepp (Plantfume 103 or Dithio), to control any remaining whiteflies. Sulfotepp is a fumigant (=vapor) pesticide, and will penetrate into crop areas that cannot be easily reached by sprays. Used properly, sulfotepp will not harm bracts.
