Help! Ants & Aphids on Elderberry

A strong spray of plain water is typically enough to dislodge them and kill them. If that doesn't work the next step would be insecticidal soap. It's relatively safe (please be sure to read and follow the directions for application.) Neem would be the last step if the other two steps aren't effective enough. With all of them, they are not a one and done. You will need to monitor the plant and periodically treat. When using insecticidal soap or neem oil, be sure other pollinators are not really active as it will kill them, too.