7 Mum Pests to Watch For This Season

Chrysanthemums have benefits that reach beyond the high ornament we enjoy in autumn. Their showy blooms attract beneficial insects like ladybugs, hoverflies, and lacewings, which prey on common pests like aphids and spider mites. Their intrinsic essential oils and aromatic toxins make their surrounding area less attractive to invading insects.

But, just as they attract beneficials, they don’t deter all pests and may fall prey to common insects. They even have genus-specific insect species. 

Aphids

Aphids are prolific reproducers. The sap-sucking insects feed on tissues with an indiscriminate palette that includes many plants. Chrysanthemum aphids (Macrosiphoniella sanborni) are brownish-black and affect the genus, but are just one among many types. Aphids are pear-shaped and soft-bodied in light yellow, green, pink, brown, or black. They colonize in large numbers on the undersides of leaves. 

Aphids prefer soft, new growth, including tender shoots, leaf undersides, buds, and blooms. They don’t often pose a severe threat but can stress plants. They also leave behind sugary honeydew, leading to unattractive black, sooty mold. Aphids spread fungal spores and are vectors for viruses, including mosaic virus and stunt, for which there’s no treatment.

Mums with severe infestation may show curled leaves, yellowing, and stunted growth. Symptoms of virus or fungal diseases like leaf spot, mottling, and distortion may appear.

Treatment

Spraying a strong stream of water early in the day may deter aphids by displacing them from leaves and stems. The stream detaches the mouth parts of piercing insects from their bodies. Do this as part of ongoing maintenance with recurring aphids, taking care of chrysanthemums’ brittle branches.

Natural predators are the best line of defense. Attract ladybugs, parasitic wasps, hoverflies, and lacewings with diverse blooming selections.

Since aphids congregate in numbers, pruning off impacted sections may eliminate small infestations. Horticultural soap or an oil such as neem controls infestations. Plant-based insecticidal oils include garlic extract, clove, rosemary, mint, and cinnamon oils and are effective organic controls. Follow label directions, as these treatments affect all insects, including pollinators. Time of day is essential in application.

Diatomaceous earth dusted over plants and soil may prevent the spread. The powder creates a sharp surface that damages soft-bodied insects.

To prevent aphids, water consistently to achieve evenly moist soils. Do not overfertilize. Aphids gravitate toward drought-stressed specimens over healthy, well-watered ones.

Nematodes

Foliar nematodes are difficult to see as tiny, slender roundworms. Yellow-brown spots on leaves are the initial indicator. These spots start on the lowest leaves and work their way up. They’ll eventually cover the entire leaf, which becomes dry and drops.

After spring rain or watering, they climb (or swim) up stems in the water channel to enter leaves for feeding. Foliar nematode damage may kill the perennial. Initial spots sometimes mimic the fungal disease leaf spot, which has darker black spots.

Nematodes overwinter in the soil and fallen debris from affected specimens. Amazingly, they can lie dormant for over a year in fallen leaves.

Treatment

Mulching is an excellent measure to prevent water from splashing onto the stems and foliage to prevent nematode access. Avoid overhead watering and drenching leaves and stems unnecessarily. Water is at the soil level, whether by hand, drip irrigation, or soaker hoses.

Remove and discard infected material and surrounding surface soil, keeping them away from the bed and compost pile.

Insecticidal soap may help as a treatment. Also, spray surrounding plants in severe cases (especially if the original plant warrants removal). It may help catch nematodes before they enter the tissues of otherwise healthy selections.

Spider Mites

Like aphids, spider mites are sap-suckers that live on the undersides of leaves. Two-spotted mites and others favor chrysanthemums, and with their piercing mouthparts, they feed on cellular tissue. You may not see the tiny creatures without a magnifying glass, but their fine webbing on buds, stems, and leaves gives them away. 

Colonies live near leaf veins and mid-ribs underneath leaves. The females lay eggs, and the larvae quickly feed on sap and tissues. Adults feed and produce the tight webs.

Foliage shows pale spots, light yellowing, and stippling on surfaces and may turn bronze. Leaves become stiff and curl, leading to early drop. Blooms wither and discolor.

Spider mites occur in hot, dry, and dusty conditions. They flock to mums experiencing drought stress. 

Treatment

Beneficial insects, including predatory mites, help control populations. If you detect spider mites, employ the stream of water from a hose method, as with aphids. Prune away affected parts and dispose of debris. A horticultural soap or oil helps mitigate severe cases. 

To prevent spider mites, maintain evenly moist soils. Water fluctuations give spider mites the opportunity to increase, further weakening their hosts.

Thrips

Thrips are tiny with long, narrow bodies, and adults have fringed wings. Their color ranges from translucent white to yellow, brown, and black. 

Thrips feed on flower and foliar tissues and carry viruses. When thrips infest petal tissues, blooms develop white spots or distort. Leaves may look silvery and stippled or brown and papery.

Not all thrips harm mums. Some feed on aphids and mites as natural pest control. If you see thrips but no indicators of damage, hold off on treatment. But if damage accompanies the insect, it’s easy to control them early on and with regular scouting. If you suspect thrips, gently shake stems over a piece of paper and look for dislodged pests.

Treatment

As with spider mites, predatory insects like parasitic wasps, other mites, and green lacewings naturally control thrips. Rinse the dust off plants to promote beneficials and deter tissue-feeding insects. Clip and dispose of affected sections.

Neem and horticultural soaps treat outbreaks. Spinosad, derived from a bacteria, is an orgainc treatment that disrupts their feeding and kills the insect.

Caterpillars

Caterpillars like budworms, leaf rollers, and cutworms are sometimes visitors. Budworms are caterpillars that feed on stems, leaves, and buds. Their voracious appetites cause quick damage.

The tobacco budworm feeds on buds and petals. It is most active at night, and you may notice chewed petals and budworm droppings by day.

The adult is a gray moth that lays eggs on the leaf’s undersides. The caterpillars hatch green or light rust-colored. Small holes in leaves and petals indicate early infestation. 

The population increases over the seasons as more budworms hatch, feed, and pupate in the surrounding soil to become adult moths. In addition to mums, they impact petunia, geranium, calibrachoa, ageratum, and marigolds, among other bloomers. 

Treatment

Fortunately, caterpillars are easy to spot. Hand-pick them off plants in the morning or evening when most active. In the day’s heat, they rest at the soil level near the base of the stems. Bacillus thuringiensis (BT) is a bacteria that disrupts digestion and causes caterpillars to stop feeding. It is a biological control.

Leaf Miners

Leaf miners are fly larvae that burrow and tunnel into foliage. Chrysanthemum leafminers (Chromatomyia syngenesiae) are one of the offenders. Larvae are yellow, cylindrical, and seedlike. Adult leaf miners are small black flies, often with a yellow triangle at the base of their wings.

Leaf miners leave visible pathways and punctures that deform foliage and petals. Plant parts become yellow and blotchy. The larvae feed beneath the leaf surface, leaving winding trails.

Adult leaf miners pierce leaves and petals to access sap and lay eggs. The punctures turn white for a speckled appearance on surfaces.

Fortunately, leaf miners rarely do severe damage. In heavy infestations, they’ll slow plant growth and cause leaf drop, and their mining may create openings for fungal infection.

Treatment

Lacewings and predatory wasps prey on leafminers. Remove damaged leaves that have trails through them to easily control a light infestation.

Crush trails with a pinch to squelch the interior miner. Neem oil, BT, and spinosad foliar sprays control infestations.

To prevent leaf miners, irrigate for consistent moisture. Avoid overwatering and prolonged periods of saturation. Irrigation monitoring isn’t so much for the leaf miner but for associated fungal infections like root rot that easily spread from soil to plant via the insect.

Whiteflies

Whiteflies also feed on sap and cause weakness, where leaves turn yellow and drop. Adult whiteflies are tiny and white, and you’ll notice them fluttering around foliage when disturbed.

Adult females lay eggs on leaf undersides, and nymphs hatch to feed on tissues. The adults pierce foliage to feed on sap. 

Whiteflies most often occur in areas of low airflow, like greenhouses, walled gardens, and on chrysanthemums indoors.

Treatment

Washing the undersides of leaves with a soft cloth is an option but challenging when it comes to the multitude of petite mum leaves. Neem, insecticidal soaps, and other horticultural oils are treatments in extreme cases.

Remove and destroy leaves in decline. Employ sticky traps to catch the flyers, but note that these will trap any other insects attracted to the color yellow.