Blackfly On Dahlia Bud

It doesn't pay to let aphids - such as the blackfly seen here on a dahlia bud - get out of control; they multiply incredibly quickly, as you can see from the infestation (right) of a black bean aphids on an elderberry branch. Is it any wonder a plant has difficulty coping? And that's aside from the fact that aphids also bring virus and other diseases.

CONTROL
Only certain varieties of dahlia seem to be affected by blackfly. Control as per greenfly and all other aphids, by organic or inorganic methods (see 'Troubleshooting Aphids On Rose Bud').

Pinching out the tip will remove most of the aphids and induce bushiness in this single-stemmed plant. The downside is that it delays flowering. Flowering in dahlias takes about 8 weeks from stopping (pinching out).