Question
hello Jennifer,
Recently I have lost my lemon and my mandarin tree.
The mandarin was suffering from sooty mould which I treated but failed and it passed away. I went in holidays and when i returned noticed the the lemon was looking very average,same result as the mandarin. Close examination revealed holes in the trunk which I put down to some form of boring insect. When cutting the branches while removing the tree I noticed that the branches had hollows through the middle running along the branch. These were about mm in diameter or 16th" for you. :-).The trees were both 20 years old.
My question is, can I replant in the same place with other citrus,
(lemon and mandarin) or is it a risk that the problem might still be in the soil? What precautions can I take?
I live in victoria, Australia.

Answer
Hi Wayne,

Sooty mold suggests that you had an insect problem.  Aphids, whiteflies, or other sap feeding insects are the most likely culprit.  When the insects feed, they exude a sticky substance called honeydew. Sooty mold lives on this honey dew.  In the future, you will want to routinely check your trees for evidence of insects and treat with an insecticide as early as possible.  Most insects "hide" on the underside of the leaves and you can often see them with the naked eye.  You may observe them flying up in the air when you approach the plant.  If you use a handlens or a magnifying glass, it is sometimes easier to see and identify the specific type.

As for the borers, as long as you remove the tree and as many of the large roots as possible, I think you are safe to replant in the same location.  If you cannot remove the entire trunk or roots, you may want to replant a short distance away.  The borers are most likely coming in from a nearby source and you will need to be on the lookout for them to return. Scout the tree about once a week for unusual symptoms.  With borers, you may see wood shavings on the ground under the tree.  If you observe this, then look for small entry holes.  If the borer has attacked a small branch, it can be clipped off. If it is the trunk or larger branch, there are methods for killing the borers.  I can help you if it comes to this.

Good luck!