Dahlias & Ants
The dahlia appears in a wide range of shapes, sizes and colors. There are 15 unique flower colors of dahlias recognized by the American Dahlia Society. Once established, the dahlia grows quickly. Often the appearance of ants on the plant's stem is the first indication that the dahlia has a pest problem.
A few ants climbing the stems of the dahlia often end up overlooked by the gardener, but this is normally the first tip that the dahlia is suffering from a common garden pest, the aphid. Ants are attracted to aphids because the insects produce a substance that ants love to consume. The ant poses no harm or threat to the dahlia plant.
Aphids form large colonies on the dahlia plant quite quickly. The plant will begin to show signs of leaf or bud deformation. Wilting can occur. The aphids appear as tiny red, black, brown or green dots along the stems and leaf growth. In a large infestation they will spread to the buds. The insects use their sharp, piercing mouths to suck the plant's sap by piercing its outer layers. Once the insect attaches to the plant to feed, it secretes a substance called "honeydew" that attracts the ants.
Abundance Of Ants
As the aphid colony builds the ants become more abundant traversing up the dahlia's stems. The ants climb in single file and often appear as an endless parade in their quest to consume the honeydew. If the aphid colony is prolific then the ants take up residence and will often build an ant mound nest in the dirt at the base of the dahlia to easily access the honeydew.
To eradicate the ants control must be gained over the aphid colony. Simply hosing aphids from the dahlias using water often works well. Insecticidal soap and chemical insecticides can be applied to large colonies of aphids or to prevent re-infestation. The insecticide disulfoton controls aphids for up to eight weeks, according to the Dahlia Society of California.
Once the aphid population is removed the ants will move on. The ants only stay on the dahlia to consume the honeydew of the aphid. They have no interest in the dahlia or other insects in the vicinity.