10 November 2025

Customer Question – Treating Scale on 2 Olive Trees

Q. “Dear Green Gardener Team I’m seeking advice on how to manage and recover two olive trees that are both infested with scale insects. Both trees are planted in pots and kept on the same external balcony of our 2nd–3rd floor maisonette flat. The balcony faces south and receives around five hours of sunlight in winter and 10–12 hours in summer. The first tree began showing signs of scale infestation around January this year — sooty mould buildup on the leaves leading to reduced light exposure and leaf loss. By February, we noticed ants (likely attracted to the honeydew), and by April, both trees were affected.

Our treatment steps so far :-

1. April & August: Applied Bug Clear Ultra 2 twice during the year.
2. Ongoing: Used potassium soap every 3–5 days under heavy infestation, reducing to every couple of weeks when it improved.
3. July: Began using ant powder to reduce ant activity and encourage natural predators of scale.
4. October: Despite continued potassium soap sprays (every 3–4 days), the infestation has worsened again, with heavy brown scales on branches. We’ve started selectively pruning the worst-affected areas.”

Thank you very much for your time and expertise. Courtney

A. Thanks for the message and we would always recommend the following for treating Scale :-

1. A natural spray is the a good idea as it should kill the scale and wash the honeydew away which is attracting the ants but we recommend SB Invigorator rather than Potassium Soap. This spray needs to dry to work so apply on a dry, breezy day and repeat as needed. Very similar to your potassium soap regime.
2. We then recommend Scale Nematodes to try and kill the scale insect. This involves spraying the plants with nematodes 4 times. You need to apply when the daytime temps will be 12c or above and if possible wrap the trees in bins bags after each application for 48 hours to keep the nematodes moist. If temps are too low then use SB during the winter and then use the nematodes in the spring when temps rise.

Otherwise you appear to be doing it correctly. Scale is hard to shift and I suspect your balconies are perfect for them but I have been doing this along time and the combination of SB and Nematodes has always given me the best results.

I hope this helps.

Kind regards Jon @ Green Gardener

Available to buy now