Answer: It's really difficult to diagnose a plant problem without seeing it. Here are the most common poinsettia problems; perhaps this information will help you determine just what is wrong with your plant. 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. To avoid, use well draining 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 (it can distort the bracts).
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