Chrysanthemums (Chrysanthemum morifolium, Dendranthema grandiflora), also referred to as mums, are annuals and perennials from the sunflower family. The plants come in a range of sizes and bloom during late summer and fall in shades of pink, orange, purple, yellow, red or white. A number of black bugs may infest mums.
Chrysanthemum leafminers are frequently seen in chrysanthemums that are grown in greenhouses. Another small black bug on chrysanthemum could be the chrysanthemum aphid, a sap-sucking pest that feeds on plant juice with its long mouth parts.
The adults of chrysanthemum leafminers are small gray or black flies with yellow marks. The females lay eggs in the foliage tissue and the larvae emerge after about four days. The pests complete a whole life cycle in under three weeks under optimal weather conditions. Chrysanthemum aphids are black or brown, soft, pear-shaped pests with long legs and antennae. There are distinct, tube-like protrusions referred to as cornicles growing from the back end.
Both the adults and larvae of the chrysanthemum leafminer feed on foliage. Damage is seen in the form of winding, white tunnels on the leaves. Mature larvae pupate on foliage or retreat into the soil. Infested foliage starts to dry and droops on stems. Black larvae waste is visible in the tunnels. Aphids infest foliage undersides, new stems and flowers in dense groups. The pests suck sap and produce sticky honeydew during feeding. Damage results in distorted and stunted growth and discolored flowers and foliage. The honeydew leads to the growth of sooty black mold.
Remove and destroy all foliage infested with the leafminer. Clear all foliage debris from under the plants as it may contain larvae. Use foliar systemic insecticides in cases of severe infestation; look for insecticides that contain acephate as the active ingredient. Spray aphid-infested plants with forceful jets of water a couple of times every day to dislodge the pests. Target the water on foliage undersides. Introduce beneficial insects like syrphid fly, lacewing or lady beetle. Chemical control options include malathion, acephate or permethrin.