Hi,

I'm new to growing citrus and I have inherited a lemon tree from the previous owner. The tree has been fine so far and very productive. However, when I inspect the tree today, I notice some white stuff at the end of a twig. Can someone tell me what this is and is it something that I should concern about? I have only spot one, so I hope it isn't that bad. I'm located in Northern California if that helps.

Looks like some type of fungus. Also looks like the stem to an old fruit. I would cut it back to clean wood. You will not get any growth from that piece of stem, just remove it back to the branch. I usually cut that section of stem with the fruit.