AusBonsai

I have a Leptospermum Burgundy Queen in my native mixed forest planting which has what I believe to be a scale insect infestation. They are on the branches and trunk of the tree. They are very small, only about 1/2 mm or less, appearing as tiny white specks that are difficult to remove. I have tried several times to kill them with lime sulphur and Yates Rose Shield, but only some seem to be affected by the spray with most surviving. This lepto is the only tree in the group planting that's affected.
Does anyone have a suggestion what spray I should use to get rid of these tiny critters?

Looks like some sort of scale but there are many different sorts and not all respond to the same treatments. Many scales are protected from the contact pesticides because they live under the shell. Both the products you have used are contact insecticides so they only kill bugs that the spray touches. Scales are protected and not usually affected. Oil based sprays are usually used to treat scale as that seems to coat the shells and suffocate them inside. Read the instructions as some should not be used in hot weather. Check neem oil or any other horticultural oil spray should treat scale.

Sometimes the treatment will kill the insect inside but the hard shell stays for a long time. I would pick a few off and check under the shells to see if there appears to be anything alive or juicy under there.

Agree with shibui that the hard shell can remain after scale insect itself has been “neutralised” so there is a chance the treatment you already have undertaken has done the trick.
Disagree that Rose Shield is a contact insecticide however. It’s systemic so will be effective regardless of direct contact. Might take a day or two while the active ingredients are absorbed but I think it should work. Not sure when you applied (and assume it was in line with manufacturer’s instructions)
I’d be surprised if this product didn’t have an impact on your scale issue. Check under the shells...!

You should read the specs again R3.
Rose shield does have systemic but it is the fungicide component.
Insecticide component is a pyrethroid which is a contact insecticide. The description even says it works by contact and stomach action (which I guess could be taken as systemic) but pyrethroids do not enter the plant system. They work by skin contact or by eating the chemical on the leaves.
The real evidence is there is no claim of rose shield controlling any scale.

Always check that the pest is listed on the label for effective options for control of the target pest.

Thanks shibui and R3. I did scrape off a couple of them to check, and yes, they were still alive, even though I waited several days in the hope they would die. I'll try the white oil, and failing that I'll resort to physically removing them. I will win!

White oil is an older treatment and can have side effects, especially in warm weather. Newer oil treatments include extras for more efficiency and less undesirable effects on the plants. Look for eco oil, pest oil or neem oil as more plant friendly alternatives. You can even make your own white oil. It is just a vegetable oil emulsified in water with some soap or detergent - here's one recipe https://www.leafrootfruit.com.au/white-oil/

If there are not too many scales and you have the time dabbing the shells with metho is reported effective but will only kill the ones you touch. New ones will still hatch and any you miss will keep eating and breeding. repeat regularly to get good control.
I have also sprayed with metho. It evaporates quickly at room temp and does not seem to harm the trees.

shibui wrote: ↑February 7th, 2021, 9:22 pm You should read the specs again R3.
Rose shield does have systemic but it is the fungicide component.
Insecticide component is a pyrethroid which is a contact insecticide. The description even says it works by contact and stomach action (which I guess could be taken as systemic) but pyrethroids do not enter the plant system.

Aha... bamboozled by the semantics I guess! Thanks for the correction and clarification, I never really picked up the differentiation between the two (fungicide and insecticide components) and so assumed it was a complete systemic, although I did wonder why I would need to thoroughly coat both upper and underside of foliage (as advised on the bottle) if that was the case. Should have investigated further from that point ... always learning!