This is the leaf of my Poinsettia. I bought it just two days ago from a local nursery. It came with these tiny yellow, black, white spots which look like pest. The white ones are definitely some kind of pest. The plant has attracted many black ants onto itself too. There are many other infested leaves. Can you tell me how i can get rid of these? Are these gonna harm the plant? Please help.
Looks like an aphid infestation, you mention ants as well, they milk these aphids for their honeydew. The aphids suck the sap from the plants, so they are indeed a pest. There are many ways to control them (but not all are very successful is my experience). You can spray them with poison or with soapy water, or with methylated spirit. You can also just wipe them off everytime you see such an infestation. Here more info about pest control of aphids, good luck with it.
They are most probably white flies. They suck the sap out of the leaf. If they are not evacuated at an early stage your plant will struggle to grow later on.
You can follow any one of these steps to remove them:-
1) Use water from a hosepipe
2) Use detergent water, which will damage their wings, eventually killing them
3) Use any organic insecticide
4) Manually remove them without damaging the leaf(not recommended)
5) Whiteflies and aphids don't like sunlight, that explains why they stay under the leaf, so you can put mirrors or aluminium foil to reflect sunlight to the bottom of the leaf
I recommend step step 1 and 2 for best results!
It is a white fly , it sucks the plant sap at underneath the leaves & , produces honey dew which attracts the ants and transmits virus... It is hard to get rid of it... Anyhow use a mineral oil and spray it under the leaves for 2or 3 times at 10 days interval It is more safer than a pesticides.... Happy gardening