Poinsettias may be affected by crown, collar and root rot, caused by Pythium sp., Rhizoctonia sp., Thielaviopsis sp. and Phytophthora sp. Overwatering or poorly drained potting soil can encourage these fungi. Use properly drained potting soil and allow the top of the soil to dry out between waterings.
The most common insect pest of poinsettias is whitefly. Inspect the undersides of leaves regularly for clumps of eggs and greenish, transparent larvae. Use sticky yellow traps or a small vacuum to remove adults. Use insecticidal soap as a last resort.
Poinsettias have long suffered from bad press. Many studies have shown, however, that their potential toxicity has been greatly exaggerated. The plants secrete a latex that is said to contain one or more substances causing local irritation of the mucous membranes, eyes and skin.
Ingesting poinsettias may cause mild to severe digestive problems (abdominal cramps, nausea, vomiting) and diarrhea in the most serious cases. The latex may also cause dermatitis in sensitive individuals. These plants aren't fatal, but as a precaution they should be kept out of children's reach.