There appear to be borers in a tibouchina. There are a few holes in the branches/trunk with a dry dark substance around the holes. Is there anything else I can do apart from removing the dry substance? The plant appears healthy.
08 October 2019 11:52 PM
The most important thing to do now that you have discovered that the plant has been attacked by borers, is to keep it healthy. Because the grubs tunnel underneath the bark, there is not a product that we could recommend to contact and kill this pest. You can probe the hole with a piece of wire to contact and kill the grub that way. You may need to prune the dead part of the branches of the tree where the grub has been active and has caused dieback. To keep the tree healthy, apply a slow release fertiliser at this stage e.g. Acticote to give your plant the nutrients it will need to help it to continue to grow and feed it over a 12 month period. You can also give your Tibouchina regular applications of seaweed extract to help it to recover.