Q. Something is eating the leaves on my lemon tree. What can I use to prevent this? I found a product at the nursery and it says you can apply it to the soil to control bugs. A. If something is eating the leaves I would not be too concerned unless it is really eating a lot of leaves. We really have to be careful when we apply these types of poisons on the soil and around the food we eat.             If this insecticide is taken up through the roots and spread through the plant to kill a bug, we might also have small amounts in the fruit as well. The insecticide dissolves in water and moves down through the soil where it is absorbed by the roots. Once absorbed, it moves up through the plant providing protection from insects.             These types of products are called systemic insecticides and move into new growth after the application. The insecticide stays inside the plant and gives it protection from bugs. Rain or water cannot wash off this internal protection and you cannot wash it off by scrubbing the fruit.             There is an old saying, “The dose makes the poison.”  Insects, because they are small, require less of a poison to kill them than larger animals.  Even though insecticides have a label to tell you what you can or cannot apply it on, it does not mean that the product is entirely safe.             If you have to use an insecticide to control damaging insects, then I would recommend something that you spray on the outside of the plant rather than something which is taken up by the plants through its roots. In many cases, these insecticides which are sprayed on the plant will wash off or degrade in the environment.             It is up to you as the consumer whether you want to purchase this product and use it. As for me, I would not eat the fruit from a tree where an insecticide was applied to the soil and taken up by plant roots.