Small sticky blobs or spots on leaves and fruit of an indoor lemon tree-what may be the cause?

Question

This occurs annually from about May/June. The tree is kept in a conservatory.
Can’t send photo-don’t know how.

Answer 1

You have bugs! It may not be aphids, but it could be scale, whiteflies, or mealybugs. Insects can be microscopic, but they leave behind "honeydew," and that's most likely what you're seeing. Treat your tree with neem oil, following the instructions in this article for treating sooty mold fungus:
https://www.gardeningknowhow.com/edible/fruits/lemons/common-lemon-tree-diseases.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/pests-of-lemon-trees.htm