How to treat fungus on indoor avocado plant leaves

Question

I have an indoor avocado plant which I just repotted but up until this point have really neglected. Despite this it seems to have grown happily over the last two years and hasn't required or received much attention.

I would like to take better care of it and in repotting I noticed that there is potentially some fungus growing on some of the leaves as shown here:

I do not know if it is a fungus or not but the white speckles seen most easily at the top of the leaf cannot be easily rubbed off the leaf and feel a bit hard to touch. These spots are on about 50% of the leaves (maybe a bit less). The rest of the plants' leaves look very healthy in my opinion:

I would like to know if there is anything I should do in this situation? I have read that I should both leave and cut off any leaves with fungus on. That I can buy some anti-fungal stuff for the leaves etc. Is there anything I should do to help the plant?

Some of the tips of the leaves are also brown. I read that this is probably due to a high concentration level of salts in the soil and have since repotted the plant to try and fix that issue. I am assuming the brown leaf tips and the fungus are unrelated.

Answer 1

Fungus on the leaves of plants growing indoors is rare due to the low humidity levels. It is more common to find virus/fungus/bacteria infections from over watering. This causes spots on the leaves which do not look like what you have.

This could be:

• pesticide residue from the grower. Seems unlikely if you have had the plant for a while
• hard water stains from overhead watering. Again unlikely if you grew it from the pit
• spider mites
• powdery mildew

Given the other problems you have with the plant I do not recommend more stress to the plant. Just get a cloth soaked in a solution of 5 ml dish soap to 1 liter of water and wipe the leaves. Rinse the cloth in water and wipe the leaves to remove the soap. Repeat three times at five to six day intervals.

This should take care of possible insect pests. If it is a fungus like powdery mildew the treatments will slow it down. If it returns just detach the leaves with problems.