While checking on plants in our greenhouse, our small potted olive tree appeared to be dying. With Spring only a few weeks away, it should have been sprouting new growth. Instead, its leaves were dirty and/or turning brown. There were also a lot of ants traveling along its branches. And on closer inspection, there were very small bumps in varying sizes attached along the length of the olive tree’s trunk.
As it turns out, these bumps are known as Black Scale (Saissetia oleae), a parasitic insect. And as these scalesfeed on your olive tree they excrete a sweet, sticky honeydew like substance. Not only does this substance attract ants, it leaves a heavy film on the olive tree’s leaves. And this film can encourage a sooty fungus to grow.
Because our tree was small and potted, it was easier to use a small mister to treat it. If it had been one of our larger outdoor trees, we would have used a garden sprayer to apply treatment.
Within two weeks of treatment, our poor olive tree started to look better. It started to put out tiny leaf buds, so we rewarded it with a light misting of seaweed extract to encourage it along.
If you have an unhealthy or stunted olive tree that is showing signs fo Black Scale infestation like ours, here’s how we managed to revive the poor tree.
If Possible, Remove The Scales
Before you begin, place some plastic around the base of the tree. This will catch the scales and any eggs, rather than letting them drop into the soil and possibly emerge later. It will also protect any non-target plants from overspray (we had dill planted in the base of our planter that we wanted to protect).
Our tree was small, so we were able to quickly scrape off most of the scales using a dull knife. The dome-shaped scales can house thousands of eggs, and the domes might also shieldmany of them when you apply the treatment, so scraping ensures better coverage. However, this might not be practical if you have a large tree. In this case, you may need to treat the tree several times.
Here’s a close up of the trunk of our olive tree showing the black scales.
DIY Black Scale Treatment Recipe
This recipe uses a two-pronged approach; Neem to kill nibbling scalesand oil to smother them.
Supplies Needed
- Neem Oil
- Olive Oil (canola oil or any other non petroleum-based oil)
- Dish Detergent (we prefer Dawn, since it’s safe for washing oiled wildlife at 5%)
- Sprayer, either small mister or garden sprayer
Mixing For Use In A Small Mister
- 1/2 Tsp Neem
- 1/2 Tsp Olive Oil
- small drop of dish detergent
- 2 C water
Mixing For Use In a One Gallon Garden Sprayer
- 4 Tsp Neem
- 4 Tsp Olive Oil
- 1 Tsp dish detergent
- 1 Gallon Water
Directions
- Add all the ingredients into your sprayer and shake to mix thoroughly.
- Beginning at the base of the trunk, spray the entire tree as well as the tops and undersides of leaves.
- Allow the spray to dry (usually within 30 minutes), then reapply
- Reapply in two weeks if needed
