Sooty Mould On The Holly Bush - How To Deal With The Ants And Aphids?

Earlier this summer, towards the end of June, I was presented with an odd sight on my holly bush. As the above photo shows the undersides of many of the new growth leaves were coated with a think sticky mould which in turn was covered in some kind of aphid infestation. Turns out that this was 'Sooty Mould'. To top it off the areas that were affected were crawling with ants. This is shown to a lesser extent in the picture below. All very odd. Well in the overall scheme of nature, not the oddest thing you will ever see, that award possibly goes to the platypus, but in small time gardening land perhaps an issue to deal with.

Sooty mould apparently doesn't infect plants, as such, but grows on surfaces where honeydew accumulates. Honeydew is a sweet sticky liquid that plant sucking insects, such as aphids, excrete after consuming sap from the impacted plant. The aphids cannot completely digest all of the nutrients in the sap and therefore excrete what is left as a sticky substance known as honeydew. So honeydew it turns out is a rather gentle way of naming aphid crap ;-). I thought it sounded nice until I figured out how it was made. I wonder if the key ingredient in Honeydew Organic Beer is aphid crap? Hmmm I might have to think twice before buying one again. Still, if it is, at least it is organic aphid crap they use ;-)

So it turns out that ants really get off on honeydew. It's similar to the ant behaviour that I saw on the Peonies in May, where apparently peonies excrete small amounts of nectar to encourage the ants en mass to wander around the peony bulbs in a high. The ants in turn apparently help the peony bulbs bloom. A tidy nice little ecosystem. One not worth messing with. Whatever you do don't try and get rid of the ants on your peonies!

In this case however the ants, who are apparently over enjoying the honeydew, go out of their way to protect the aphids who are consuming the holly bush's sap. A tidy little ecosystem whereby the aphids are protected by the ants, who are in turn, it seems, paid in an endless supply of aphid crap! Each to their own I guess! ;-)

There are various suggestions about how to control the sooty mould, but all in all, a healthy plant should more than be more than able to handle small amounts of it. Suggestions range from spraying with soapy water to using chemicals pesticides to remove. In honesty I did neither. I kept an eye on it, and gradually cut out the infected areas. After a while the rest disappeared of its own accord. If the holly bush had been completely infected then I think I might have taken more drastic measures. In this case though who am I to argue with the nice little party the aphids and the ants were having. It didn't impact the plant or the garden unduly, so why not let them have their summer fun!

Cheers

m