I've got two Orange trees and two avocado trees in my backyard. One of the orange trees looks to be the victim of a disease and has sooty mold on it. From what I have read this is usually due to animals which excrete honeydew which allows for this to occur. To attack this at the source I need to get rid of the animal/insect issue. Has anyone had a good experience or have any recommendations on which pesticide chemicals to use. If need be, I can hold back on eating the fruit for a year to resolve this issue (if the pesticide is not safe for consumption) as I have already started to see certain branches die off due to this.

The pesticide I have tried is "Ortho Elementals Garden Insect Killer" in a spray bottle which has the active ingredients of "Pyrethrins (0.01%), Canola Oil (1%) and other (98.99%)". It seems to have worked to a certain degree but was expensive. If I can get a recommendation on the right chemical to use then I can buy it in greater bulk online after testing it out. In a perfect world I would like to have something I can universally spray on both orange trees and avocado plants.

If I am taking the wrong approach to this then please let me know. Thank you for taking the time to read this.

  • 2
    My policy: Know thy enemy. That said, you should always id the culprit first, then choose appropriate counter-meassures.
    – Stephie
    Nov 25, 2015 at 22:33
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    Close up picture of the underside of the leaves of both trees please
    – kevinskio
    Nov 26, 2015 at 10:43
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    You don't want a 'universal spray', that is the wrong approach. Only apply pesticides if you have a known problem, and have identified the source. Then apply an appropriate pesticide at the proper strength. For your ornge tree, we can't help until we have a closeup picture of the mold on the leaves, so we can identify the parasite.
    – J. Musser
    Dec 3, 2015 at 3:45

3 Answers 3


You probably have an Aphid problem - it's not a disease per se and it's not mold, just an infestation. They leave the white gooey stuff on the bottom of the leaves. I use Bug-B-Gone and it seems to work fine. You can buy it in a concentrate and then mix with water and spray with a spray bottle. I think it's about 15 bucks from Home Cheapo or amazon. If you have a major problem, as in a ton of leaves are affected, then you will likely need to prune the tree to get rid of excess foliage to let in air. It is also helpful to spray down the tree with a hose every other week or so - this removes dust which they tend to thrive in.

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    It might be aphids, it could be citrus scale or even mealybug. As others have said "Know your enemy" for best results
    – kevinskio
    Jan 12, 2016 at 17:33

You could try washing off the sooty mould with a wash containing a weak solution of soap, if you have aphids they can be farmed by ants who then feed on the sticky exudate. Do you have ants crawling up and down the stems and branches? You could also try ensuring that there is enough air flow around the branches to minimise the mould. placing a bird box very close or in the trees to encourage birds nesting who will feed off any aphids, or an insect house to accommodate beneficial insects like ladybirds who will along with their larvae feed off the aphids too, all might help. On line pesticide purchases can prove problematic. For Europe on-line buying, you can purchase and import sprays and chemicals that are banned from use in the uk. There is sometimes no way of telling you are getting the chemicals you want in the concentrations you need unless from a reputable source. This may also apply to different states in the US?


Assuming you've not yet isolated and treated the infestation, and without the requested photographs showing the problem, the most likely cause is, in fact, scale insect, but even were it aphid, neem spray or a horticultural oil spray should work, though you would need repeat treatments. You are right when you say sooty mould is a consequence of an infestation, though any infestation is by insects rather than animals, and dealing with the infestation means the sooty mould will eventually disappear without specific treatment - the link below gives extensive information in regard to Sooty Mould and its causes, prevention and treatment in general


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