Why are my chrysanthemum leaves curling?

Chrysanthemum leaves curl most commonly due to aphids, thrips, or powdery mildew. The chrysanthemum aphid (Macrosiphoniella sanborni) is a host-specific, dark brown to black aphid that colonies the stem tips and leaf undersides of chrysanthemums, causing the leaves to curl, pucker, and turn yellow; it is one of the most common and damaging pests of chrysanthemums in gardens and greenhouses worldwide. Thrips rasp the leaf surface and cause the leaves to curl upward with a characteristic silvery-gray streaking and distortion of the tissue. Powdery mildew is extremely common on chrysanthemums in late summer and early autumn, producing a white powdery coating and causing the affected leaves to curl upward and eventually yellow. Spider mites also cause leaf curl and stippling in hot, dry conditions.

What causes chrysanthemum leaves to curl and turn yellow?

Chrysanthemum leaves curling alongside yellowing most commonly indicate a heavy aphid infestation, powdery mildew, or chrysanthemum stunt viroid infection. Chrysanthemum aphids (Macrosiphoniella sanborni) are dark, nearly black aphids that are highly specific to chrysanthemums; dense colonies sap the plant's vigor, causing the leaves to curl, yellow, and drop. Honeydew deposits from the aphids also promote black sooty mold on the foliage. Powdery mildew causes a progressive yellowing of the leaf following the initial white coating and curling; affected leaves eventually dry and drop. Chrysanthemum stunt viroid (CSVd) is a serious pathogen of chrysanthemums that causes the plant to become stunted and the leaves to curl, yellow, and become smaller than normal; infected plants also flower earlier than normal and the flowers may be smaller and distorted. CSVd spreads through vegetative propagation and on contaminated tools; there is no cure and infected plants must be discarded.

Why are my chrysanthemum leaves curling with white marks or streaking?

Chrysanthemum leaves with a silvery, white-streaked, or bronze-streaked appearance alongside curling and distortion most commonly indicate thrips infestation. Thrips are narrow, fast-moving insects about 1 to 2 mm long that rasp the leaf surface and feed on the cell contents, leaving behind the characteristic silver-gray feeding scars. The leaves curl upward in response to the cellular damage, and the new growth at the shoot tips is often the most severely distorted. Black specks of thrips frass may be visible on the leaf surface alongside the silver feeding marks. Western flower thrips (Frankliniella occidentalis) is the most common species and is also capable of transmitting Tomato spotted wilt virus (TSWV) to chrysanthemums, which causes additional symptoms including brown rings and streaks on the stems and leaves. Blue sticky traps placed among plants attract and monitor adult thrip populations. Apply spinosad or insecticidal soap to the foliage, covering both surfaces thoroughly, and repeat at five-day intervals.

Chrysanthemum Leaves Curling — Why It Happens and How to Fix It

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At a glance

Dark-colored aphid clusters on stems and leaf undersides, leaves curling yellow: Chrysanthemum aphid; water blast, insecticidal soap
Leaves curling with silver streaking or stippling, tiny fast-moving insects: Thrips; spinosad spray, blue sticky traps
White powdery coating with upward leaf curl in late summer: Powdery mildew; improve air circulation, apply neem oil
Fine webbing on leaf undersides, stippled, curling leaves in dry heat: Spider mites; increase humidity, apply neem oil
Pale serpentine trails visible inside leaves, curling and browning: Chrysanthemum leafminer; remove affected leaves, apply insecticide

Why chrysanthemum leaves curl

Chrysanthemums (Chrysanthemum morifolium, Dendranthema cultivars, and garden mums) are among the most widely grown ornamental flowering plants in the world, valued for their diversity of flower forms and their late-season color. They are prone to a characteristic suite of pest and disease problems, several of which are specific to chrysanthemums or the daisy family. Leaf curl on chrysanthemum most commonly signals aphids, thrips, or powdery mildew, each of which produces recognizable secondary signs that make diagnosis straightforward.

Cause 1: Chrysanthemum aphids

Signs: Dense colonies of dark brown to nearly black, pear-shaped insects cover the stem tips, flower buds, and leaf undersides. The leaves curl, pucker, and turn yellow. Honeydew makes the foliage sticky, and black sooty mold may coat the affected parts. The chrysanthemum aphid (Macrosiphoniella sanborni) is distinctive for its dark color and its specificity to chrysanthemum; it is one of the few aphids that feeds almost exclusively on a single plant genus. Infestations can build rapidly under greenhouse conditions or in still, sheltered garden positions.

Why it happens: Chrysanthemum aphids overwinter on chrysanthemum crowns and stem debris and begin reproducing in spring. They are less affected by natural predators than many generalist aphid species, partly because their dark color makes them less visible to predatory insects and partly because their host specificity means predator populations do not build in the same way as they do around more diverse aphid communities. Overcrowded, unventilated growing conditions encourage population explosions.

Fix: Blast aphid colonies from stems with a strong stream of water. Apply insecticidal soap or neem oil, covering all surfaces including the undersides of leaves and the stem tips where aphids congregate. Repeat every five to seven days. For severe infestations in enclosed spaces, pyrethrin-based insecticides are effective. Remove and dispose of heavily infested shoot tips. Inspect plants thoroughly when purchasing or accepting divisions, as aphid colonies on crowns are easy to import unknowingly.

Cause 2: Thrips

Signs: The leaves develop silvery-gray or bronze streaks and flecking where the feeding scars are concentrated. The new growth and stem tips curl upward and are distorted. Tiny, dark frass specks are visible on the leaf surface. Adult thrips are narrow, 1 to 2 mm long, and move rapidly when disturbed; they are most easily spotted by tapping a stem over a white sheet of paper. Western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci) are the most common species on chrysanthemum.

Why it happens: Thrips are attracted to chrysanthemum flowers and foliage throughout the growing season. They enter buds and feed on developing tissue, causing the characteristic distortion of new growth. Western flower thrips is also a vector for Tomato spotted wilt virus (TSWV), which causes brown ring spots, stem streaking, and additional leaf distortion on infected chrysanthemums. Thrip populations peak in summer and are worst in hot, dry conditions.

Fix: Apply spinosad as a foliar spray, which is highly effective against thrips and has low toxicity to beneficial insects once dried. Insecticidal soap and neem oil provide some control but require direct contact and thorough coverage. Place blue or yellow sticky traps among plants to monitor adult populations. Remove and dispose of heavily infested flower buds and stem tips. For plants that develop Tomato spotted wilt virus symptoms alongside thrip damage, remove the entire plant as it cannot recover.

Cause 3: Powdery mildew

Signs: A white to gray powdery coating develops on the upper surfaces of the leaves in late summer and early autumn. Affected leaves curl upward, yellow, and eventually drop. The mildew is worst in warm, humid weather with still air, particularly in garden beds where chrysanthemums are growing densely and air circulation is limited. Chrysanthemums are among the most susceptible plants to powdery mildew; the disease can be severe enough to defoliate the lower half of the plant by flowering time.

Why it happens: Powdery mildew on chrysanthemum is caused primarily by Golovinomyces cichoracearum. Unlike most fungal diseases, it thrives in warm, relatively dry conditions with high humidity; it does not require wet leaves to infect. The dense, branched growth habit of garden mums creates the still, humid microclimate the fungus prefers. Susceptibility varies among cultivars but the disease is present in virtually all chrysanthemum collections by late summer.

Fix: Improve air circulation by spacing plants at least 18 to 24 inches apart and avoiding planting next to walls or fences that restrict airflow. Apply neem oil, potassium bicarbonate, or a copper-based fungicide at the first sign of infection; preventive applications from midsummer are more effective than trying to control established colonies. Remove mildewed leaves and all plant debris in autumn. Select less susceptible cultivars; many modern garden mum varieties have improved mildew resistance compared to older types.

Cause 4: Spider mites

Signs: The leaves develop a fine stippling or bronzing, starting at the stem tips and working downward. The leaf surface looks dusty or dull. Fine webbing appears on the undersides of leaves and between stems in heavy infestations. The leaves curl as the feeding damage accumulates. Spider mites thrive in hot, dry conditions and their populations can explode rapidly in warm summers, particularly on plants that are drought-stressed or in sheltered positions with little rain to knock populations back.

Why it happens: Two-spotted spider mites (Tetranychus urticae) are common on chrysanthemums in summer, particularly in greenhouses and hot, sheltered garden positions. Drought stress and dusty conditions favor mite population growth. Broad-spectrum insecticide use that kills natural mite predators is a common trigger for mite outbreaks on chrysanthemums that were previously unaffected.

Fix: Apply neem oil or insecticidal soap to the undersides of leaves, where mites concentrate, and repeat every five to seven days. Increase humidity by misting and by watering the soil around plants. Avoid water-stressed conditions. Predatory mites (Phytoseiulus persimilis) are effective biocontrol agents in greenhouse settings. Do not use broad-spectrum insecticides that eliminate natural predators.

Cause 5: Chrysanthemum leafminer

Signs: Pale, serpentine or blotch-shaped trails are visible inside the leaves when held up to the light, created by fly larvae tunneling between the upper and lower leaf surfaces. Affected leaves curl, yellow, and may drop. The entry and exit punctures of the adult fly may also be visible as tiny white dots on the leaf surface. Leafminer damage is most common in late spring and summer and affects the lower and outer leaves first.

Why it happens: The chrysanthemum leafminer (Phytomyza syngenesiae and related Liriomyza species) is a small fly whose larvae mine inside the leaf tissue after the female lays eggs in the leaf. The larvae feed as they tunnel, killing the tissue along their path. Multiple generations occur per year and infestations can escalate quickly if not addressed early. The damage weakens the plant and, in heavy infestations, significantly reduces photosynthetic capacity.

Fix: Remove and dispose of heavily mined leaves promptly. Apply a systemic insecticide containing spinosad or abamectin, which is taken up by the plant and kills the larvae inside the leaf where sprays cannot reach them. Neem oil has some deterrent effect on egg-laying adults. Yellow sticky traps catch adult flies and help monitor populations. Avoid broad-spectrum insecticides that eliminate parasitoid wasps, which are the most important natural enemies of leafminer flies.

Chrysanthemum Leaves Curling