Chrysanthemums attract a handful of common insect pests, but most can be managed with simple physical controls and careful monitoring before you ever need to reach for a spray bottle. Aphids, spider mites, thrips, and leafminers are the main culprits, and each leaves distinct signs on your plants that tell you exactly what you’re dealing with.
The Most Common Chrysanthemum Pests
Aphids are the pest you’ll encounter most often. These small, soft-bodied insects cluster on new growth and the undersides of leaves, sucking plant sap and leaving behind a sticky residue called honeydew. Heavy infestations cause curled, yellowing leaves and stunted shoots. You may also notice a black, sooty mold growing on the honeydew, which is unsightly but not directly harmful to the plant.
Spider mites are tiny, nearly invisible to the naked eye, and thrive in hot, dry conditions. Look for fine stippling (tiny pale dots) on the upper leaf surface and, in worse cases, delicate webbing between leaves and stems. By the time webbing is visible, the population is already large. Mites reproduce rapidly in summer heat, so catching them early matters.
Thrips are slender insects that rasp the surface of petals and leaves, leaving silvery streaks or distorted, brown-edged flowers. Western flower thrips are especially problematic because they also transmit viruses. In a greenhouse setting, a general monitoring guideline from Rutgers Cooperative Extension suggests action when sticky traps catch around 15 thrips per card per week in a 1,000-square-foot area.
Leafminers tunnel between the upper and lower surfaces of leaves, creating winding, pale trails you can easily spot. The larvae feed inside the leaf tissue, so they’re protected from most contact sprays. Damage is mostly cosmetic on established plants but can weaken young ones if severe.
Start With Water and Physical Controls
A strong jet of water aimed at the undersides of leaves is surprisingly effective against aphids and spider mites. It physically knocks the insects off the plant and disrupts their feeding. Repeat this every two days, and plan on at least three treatments to meaningfully suppress the population. This works best on sturdy, established plants where you can direct the spray without snapping stems.
For thrips and leafminers, physical controls are less effective because thrips hide inside flower buds and leafminer larvae are protected within the leaf. Removing and discarding heavily infested leaves or spent blooms reduces the number of pests completing their life cycle. Don’t compost infested plant material; bag it and throw it away.
Encouraging Beneficial Insects
Before spraying anything, consider what’s already working in your garden. Ladybugs, lacewings, hoverfly larvae, and parasitic wasps all feed on aphids and can keep populations below damaging levels without any intervention from you. The key is avoiding broad-spectrum insecticide use that kills these helpers along with the pests. Once you wipe out beneficial insects, aphid and mite populations often rebound faster and harder because their natural checks are gone.
If you’re growing chrysanthemums in a garden bed rather than a greenhouse, planting a diverse mix of flowering plants nearby helps attract and sustain predator populations throughout the season. Letting a few small herbs bolt and bloom, for example, gives parasitic wasps a nectar source they need to thrive.
Low-Toxicity Sprays
When water sprays and beneficial insects aren’t enough, insecticidal soap and horticultural oil are the first chemical options to consider. Both work on contact, meaning they need to physically coat the pest to be effective. They break down quickly and pose minimal risk to beneficial insects once dry.
Insecticidal soap works well against soft-bodied pests like aphids, spider mites, and young thrips. Horticultural oil smothers insects and eggs on contact and is particularly useful against mites. Both require thorough coverage, including the undersides of leaves where pests concentrate.
There are important limits to keep in mind. Both soap and oil sprays can burn foliage if applied when temperatures exceed 90°F, in direct midday sun, or when plants are drought-stressed. High humidity that prevents leaves from drying quickly also increases the risk. Only use commercially formulated insecticidal soap, not household dish soap, which contains additives that are much more likely to damage leaves. Essential oils sold as “natural” pest sprays are less refined than horticultural oils and carry a higher risk of foliage burn as well.
If you’ve recently applied a sulfur-based fungicide to your chrysanthemums, avoid following up with horticultural oil. The combination of sulfur and oil on leaf surfaces can cause significant damage to the plant.
When Stronger Products Are Needed
If natural predators and low-toxicity sprays aren’t controlling the problem and you’re seeing serious plant damage, synthetic insecticides are an option. Products containing permethrin or bifenthrin are broad-spectrum and effective against most chrysanthemum pests. Malathion is another option that works against aphids and mites. These products kill on contact or shortly after ingestion and provide some residual activity on leaf surfaces.
The tradeoff is real: broad-spectrum products kill beneficial insects indiscriminately. A single application can set back your garden’s natural pest-control ecosystem for weeks. If you do use them, apply in the evening when pollinators are less active, and target only the affected plants rather than spraying an entire bed.
For leafminers specifically, contact sprays have limited effectiveness because the larvae are inside the leaf. Systemic insecticides, which the plant absorbs and distributes through its tissues, are more effective against leafminers but also affect any insect feeding on the plant, including pollinators visiting the flowers. This makes them a poor choice for chrysanthemums in bloom.
Monitoring and Prevention
Catching problems early is far easier than fighting an established infestation. Check your plants at least once a week, paying close attention to the undersides of leaves and the growing tips where new growth emerges. If you’re growing in a greenhouse, placing one yellow sticky trap per 1,000 square feet of growing area, positioned at canopy height, gives you an early warning system for flying pests like thrips and whiteflies. Check the traps weekly and look for trends in the numbers.
Good cultural practices reduce pest pressure before it starts. Space plants far enough apart for air to circulate freely, which discourages spider mites that thrive in stagnant, humid microclimates. Water at the base of the plant rather than overhead to keep foliage dry (except when you’re deliberately spraying to dislodge aphids). Remove dead leaves and spent flowers promptly, as decaying plant material harbors pests and diseases. At the end of the growing season, clear all chrysanthemum debris from the bed to eliminate overwintering sites.
Healthy, well-watered, properly fertilized chrysanthemums tolerate moderate pest feeding with minimal visible damage. A stressed plant, on the other hand, shows damage faster and recovers more slowly. Keeping your plants in good overall condition is the most effective long-term pest control strategy you have.