Chrysanthemums, commonly known as mums, are popular flowering plants that provide vibrant color to gardens well into the autumn season. Although robust, they are susceptible to insect and mite infestations that compromise their health and appearance. Addressing these issues requires a practical, step-by-step approach, moving from prevention and non-chemical methods to targeted treatments only when necessary. Understanding the specific nature of the infestation is the first step toward successful management.
Identifying the Most Common Mum Pests
Identifying the specific pest is necessary, as different organisms require different management approaches. Aphids are small, soft-bodied insects, often dark brown or greenish-black, that cluster on new growth and flower buds. Their feeding distorts leaves and stunts growth, leaving behind a sticky waste product called honeydew. Honeydew often encourages the growth of black sooty mold fungus, which further detracts from the plant’s appearance.
Spider mites, which are arachnids, are extremely small and thrive during hot, dry weather. They puncture plant tissue, resulting in fine yellow spots, known as stippling, on the leaves. A telltale sign of a spider mite colony is the presence of fine silk webbing around buds, stems, and on the undersides of the foliage.
Thrips are minute, slender insects that feed on foliage and flower tissues, causing a silvery, stippled, or streaked appearance. When thrips feed on petals, blooms may become discolored or distorted, and black specks of excrement are often found nearby. Whiteflies are tiny, winged insects that flutter up when the plant is disturbed. Like aphids, they suck plant sap and excrete honeydew, causing leaves to yellow and drop.
Leafminers are the larvae of small flies that tunnel within the leaf tissue. As they consume the tissue, they leave behind characteristic winding, pale trails. Severe leafminer activity can cause sections of the foliage to dry up and droop, weakening the overall plant structure.
Cultural Practices for Prevention
Maintaining optimal environmental conditions minimizes the likelihood of pest outbreaks. Proper plant spacing allows for sufficient air circulation around the foliage. Good airflow helps leaves dry quickly, discouraging fungal diseases and reducing the humid conditions preferred by pests like spider mites and whiteflies.
Consistent and appropriate watering is a preventative measure, as plants under water stress are more vulnerable to infestation. Mums require regular irrigation, but avoid overwatering, especially as the plants approach flowering. Poorly drained, overly wet soil can lead to root issues that compromise the plant’s natural defenses.
Sanitation practices remove potential hiding spots and breeding grounds. Regularly removing fallen leaves and debris from around the base of the mum eliminates sites where insects or eggs may overwinter. Controlling nearby weeds is also helpful, as they can harbor pests and viral diseases that transfer to the mums. Fertilization should be applied judiciously, as excessive nitrogen can make foliage more attractive to sucking insects like aphids and mites.
First-Line Organic and Manual Treatments
When a pest population is noticed, the least chemically intensive methods should be implemented immediately to knock back the numbers. For localized, small populations, manually removing pests or pruning severely infested leaves and buds can be highly effective. A powerful, targeted spray of water from a garden hose can physically dislodge soft-bodied pests like aphids and whiteflies from the plant.
Insecticidal soaps are a recommended first-line treatment for soft-bodied pests because they work only upon contact. The soap’s fatty acids penetrate the insect’s protective outer layer, known as the cuticle, leading to rapid dehydration and death. Because these soaps have no residual activity once the spray dries, they pose minimal risk to beneficial insects.
The soap mixture must thoroughly wet all surfaces of the infested foliage, paying particular attention to the undersides of the leaves where pests often hide. Applying the solution in the early morning or late evening is preferable, as spraying during peak sun or when temperatures exceed 90°F can cause the leaves to scorch. Use commercial insecticidal soap products, which are specifically formulated to be gentle on plants, rather than household detergents that may contain harsh additives.
Horticultural oils, which include Neem oil, function similarly by coating and suffocating pests on contact. Neem oil products that contain the compound azadirachtin also disrupt the feeding and growth cycles of certain insects. Before treating the entire plant, test a small leaf section for several days to ensure the mum is not sensitive to the product, a phenomenon known as phytotoxicity.
When to Use Targeted Insecticides
Chemical insecticides are an escalation for situations where manual and organic treatments have failed to control a widespread infestation. When selecting a product, choose a targeted insecticide, such as a specialized miticide for spider mites or a systemic product for sucking pests, to limit the impact on non-target species. Systemic products are absorbed by the plant and offer extended control, sometimes lasting six to eight weeks following a soil drench application.
Pollinator safety is a primary consideration when using any insecticide on flowering plants, as beneficial insects are highly susceptible. Avoid applying insecticide when mums are in bloom, as this presents the greatest risk to foraging pollinators. If treatment is unavoidable, applying the product in the late evening or before sunrise minimizes exposure risk, since pollinators are not actively visiting the flowers then.
For safe and effective chemical control, strictly adhere to the instructions on the product label. The label provides required application rates, specifies protective gear, and contains warnings regarding pollinator hazards and environmental safety. Using the correct application method, such as a coarse spray to reduce drift, ensures the treatment is confined to the target area.