What is this on my lemon tree
They look like little black eggs and can be picked off easily. Tree only just started fruiting
I wish you were able to include a photo but two common small black things are aphids and scale insects. See if this article on lemon tree pests helps: https://www.gardeningknowhow.com/edible/fruits/lemons/pests-of-lemon-trees.htm
Click on the blue underlined words to link to pictures and further information.