So the ants move those aphids all over the tree, spreading the problem. Strangely the obvious "how to control it" is a harmful act. When people think of a low impact insect control they think of pyrethrum, because they think of crushed up daisies and marigolds. Wrong. More later.
Step 1: Stop the ants going up the trunk. Put a ring of low impact ant sand around it.
Step 2: Let the beneficial insects do the rest. The fluffy white parts where the aphids were are parasitised aphids (thanks to a tiny wasp). And of course the big guns - ladybirds.
Ladybirds, both adult (above) and nymphal (not pretty but still black and red) are a powerhouse of aphid control. The bad news - pyrethrum will kill them stone dead.
So, it might take a few years to get the populations of beneficial insects up, but it's worth it. And stay away from pyrethrum - it's a green con.
I'm fine with chemicals. But used cleverly. If there was no fruit on this tree I'd use one called Confidor watered into the soil. I think that's how we got so many beneficials for this year. Confidor runs through the sap of the tree and controls aphids, but leaves the beneficials alone.
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