PlantLife Online

Answer

The most likely cause of liquid coming out of the leaves of the poinsettia is insect damage. It is hard to say exactly what insect is causing the damage but it is most likely one with piercing sucking mouth parts. Just as it sounds piercing sucking mouth parts do just that, piercing the cell wall and feeding on the contents of the of the cell. Below is a list of common poinsettia damaging insects some are piercing sucking others the chewing variety. You will need to do some close investigation to find the culprit. All of the insects below can be controlled with common organic and inorganic methods and chemicals. 

If you look closely and there seems to be no sign of insects it is possible the poinsettia has a fungal, bacterial or viral problem, common to many Euphorbia species. There are treatments however it might be easier and cheaper to say goodbye and get a new plant. 

-Armyworms (see also Caterpillars)
-Caterpillars (see also Armyworms and Poinsettia Hornworm)
-Fungus Gnats
-Mealybugs
-Poinsettia Hornworm (see also Caterpillars)
-Scales
-Shore Flies
-Slugs & Snails
-Spider Mites
-Thrips
-Whiteflies

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