What is this "grated parmesan" looking parasite? How can I rescue my little weed tree?

Question

I live in the Mexican Caribbean and have been observing with great interest what first seemed to be a weed and I now believe to be some kind of citrus tree in my garden (the leaves smell of lemons when you rub them. It has thorns and is now about waist height). It's growing almost through concrete (bless!) but this week the leaves have started getting covered in what looks like grated parmesan cheese and my poor little tree is looking decidedly unhealthy. What is this parasite? What can I do? Wipe it off the leaves with vinegar, perhaps? Should I try and replant the tree? I'm so impressed by this little weed's determination so far and I don't want to stand by and let it die... although my fingers are far from green and I've no idea how to help! Advice from greener fingers needed please! Help me save my little weed tree!

Answer 1

Aphids, wash the leaves with soapy water.

Answer 2

there aphids place vinigar and soap in a bottle and spray the plant late in the evening when the sun is set so u dont burn your plant and that will kill them and the vinigar will keep them from comming back just spray it down 1one a day for a week and that will solve it when u see some appear just spray it again.