We had some great photos sent through from one of our customers. These are NZ Native Manuka plants, that have developed a black sooty looking substance all over them, and the plants themselves are sickly and look like they are dying.
The black soot is caused by scale insects (the white bumps on the stems), and the boot soot is a fungus that grows on the excrement of the scale. The scale suck at the stems, so does slow the growth, and can make the plants quite sickly if the infestation is bad.
Normally fantails keep these mostly under control, but if there are not many of these, the best thing to do would be to spray the plants with Aquaticus spray, which is a natural fish oil that smothers the scale, and feeds the plants at the same time. You may need to do this 2-3 times, and it will take 3-4months before the black soot washes away.
The plants should recover, but it may take a year or so, and in that time they will still be vulnerable to another infestion.
Another good reason to have a pest control program in place to encourage the birds – much easier to use birds to keep the insect populations under control.