The problem with soap sprays are that they kill by contact. When the leaves are
rolled up, it is very difficult to coat the underside of them, to do the job.
Chemicals on the other hand form more of a mist that has a better chance of
reaching the aphids.

Sherwin D.

risingsungardens wrote:

In my opinion, chemical controls are overkill for aphids. In addition
to soap spray and ladybugs, control the ants that are likely
harvesting aphid "honeydew" by applying a sticky barrier
like tanglefoot around the trunk of the tree. Also keep in mind that
pests often attack compromised plants. Aphids tend to be associated
with drought stress. Assess the overall health of your tree.
I hope this helps.