Hi there, I was wonder If anyone could help with an issue I've been having with my potted olive tree. All over the tree are pale brown spots that can be scraped off and they keep spreading to new growth. The spots cover the entire trunk and all older leaves (both on the top and under sides). Is this scale? And if so, is there any way to stop an infestation this widespread (I've tried neem oil without much luck).
Parlatoria scales (Parlatoria oleae) are circular and pale brownish grey with a black spot in the middle. They are smaller than black scales and are considered a less serious pest on olive trees.
Horticultural oils work once the eggs have hatched, warm soapy water can be used on the whole tree (use a soft sponge to apply and rub with) and followed by treatment with the oil should help get rid of these nasties.
To confirm you will need to have a magnifying glass and lift one of the scale covers then look for the eggs under the cover.
That looks like scale to me. Here are things that I've used to varying degrees of success:
1) Soap. You can get nontoxic insecticidal soap or use a mild dish liquid mixed with water and spray it on. The soap breaks down the insects' waxy cuticle and dehydrates them. With scale it also loosens their grip and makes them easier to rub off or blast with a hose.
2) Oil. There are light oils, both mineral and vegetable, that are safe to spray on plants and typically used on fruit trees when they are dormant. The oil covers the insects' bodies and clogs their respiratory pores. I don't think olives would have a problem with an oil spray but you might want to test a branch before coating an entire tree.
3) Neem. If you use this in conjunction with soap it seems to have a quicker effect on aphids and whiteflies, but I think scale are somewhat resistant because of the way they latch on to feed. Neem requires ingestion so direct sap feeders bypass it.
4) Predators. Lacewings and ladybugs will eat the immature stages of scale, before they have developed the hard shell that makes them "invincible."
Diego Footer on Permaculture Based Homesteads - from the Eat Your Dirt Summit