Crape Myrtle

Not a pest or a disease but the most damaging thing that happens to this plant, and it is done deliberately. Topping - sawing mature trunks back to the same stubs every winter - is widely believed to make crape myrtles bloom better. It does the opposite. Each cut forces a dense cluster of weak, fast, whip-like shoots from a knuckle of scar tissue; those shoots are poorly attached, they bend to the ground under the weight of wet flower heads, and they carry fewer and coarser panicles several weeks later than an unpruned tree. The large wounds admit decay into the trunk, and the smooth exfoliating bark and vase-shaped silhouette, which are two of the three reasons to grow the plant, are lost permanently.

Watch for: Thick trunks ending abruptly in swollen knuckled stubs at a uniform height, with a shock of thin shoots radiating from each. Branches bending to the ground or snapping after summer rain, because the shoots are too weak for the flowers they carry. Bloom arriving noticeably later than on untopped trees nearby, and in smaller quantity. Cracks, hollows, and soft decayed wood at old cut faces. A canopy that has to be cut again every single year to look intentional, which is the treadmill the first cut starts.

Prevent: Choose the right size at the nursery - this is the entire prevention. Crape myrtle cultivars run from 18-inch dwarfs to 30-foot trees, and topping is almost always what happens when a tree cultivar was planted in a shrub-sized space. Match mature height to the site and no hard pruning is ever needed. Prune lightly in late winter for structure only: dead and crossing wood, thin interior twigs, basal suckers. On a tree-form, prune upward instead of downward, removing low side branches to expose the trunks. If a landscape crew offers to cut yours back, decline.

Treat: A topped tree can be rehabilitated, slowly. Starting in late winter, select the one or two strongest, best-placed shoots on each knuckle and remove all the others flush; repeat each year, gradually rebuilding a branch structure from those leaders. Expect three to five years to a natural-looking canopy, and accept that the knuckles themselves are permanent. If the tree is genuinely too large for its position, the honest fix is to remove it and replant a cultivar that fits, rather than committing to sawing it down every winter for the rest of its life.

The single most common thing done wrong to this plant in America, and worth checking before hiring anyone to prune one. Nothing about crape myrtle requires hard pruning to flower - it blooms on new growth whether or not you cut it.

An introduced felt scale (Acanthococcus lagerstroemiae) first found in Texas in 2004 and now across most of the Southeast and beyond. Unlike most scales it colonises the bark rather than the leaves, encrusting trunks, branch crotches, and pruning wounds with white-to-grey felt-like bumps. It excretes heavy honeydew, and the black sooty mold that grows on that honeydew is usually what people notice first - a tree, and everything parked beneath it, turning black. It rarely kills an established crape myrtle outright but reduces flowering, disfigures the bark that is the plant's best feature, and is difficult to eradicate once settled.

Watch for: White or grey felt-like encrustations on trunks and in branch crotches, most obvious on bare winter wood. Crushing one leaves a distinctive pink-to-red smear - the quickest confirmation there is. A black sooty film spreading over trunks, leaves, and anything beneath the tree, including cars and paving. Sticky honeydew on foliage in summer. Reduced flowering and thinner growth on heavily encrusted branches. Ants working up and down the trunks, farming the scale for its honeydew.

Prevent: Inspect nursery stock closely before buying, since the scale moves almost entirely on infested plants - check trunks and crotches, not just leaves. Do the same before accepting a transplant from a neighbour. Keep trees unstressed with adequate water in drought, avoid heavy nitrogen, and avoid wounding the bark, since egg-laying concentrates around pruning cuts and injuries. Do not top the tree: knuckled wounds are exactly where colonies establish. Protect the lady beetles that feed heavily on this scale by avoiding broad-spectrum sprays.

Treat: In late winter, wash the trunks and branches with a soft brush and mild soapy water - physically removing the felt covers and sooty mold makes everything else work better - then apply a dormant horticultural oil thoroughly to the bark, repeating as the label allows. Oil timed to the crawler stage in spring also helps. For heavy infestations a soil-applied systemic (imidacloprid or dinotefuran) is the standard extension recommendation, but crape myrtle is heavily worked by bees for pollen, so apply it AFTER flowering rather than before, follow the label exactly, and treat it as a last resort rather than a routine. Wash off the sooty mold once the scale is controlled; it lives on honeydew and disappears once the supply stops.

The defining new pest of this plant, and spreading fast. The pink smear when crushed is the field test that separates it from ordinary scale, and late winter - bare wood, no bees, easy access - is by far the best time to deal with it.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

The crapemyrtle aphid is host-specific and builds up on leaf undersides through summer. The feeding barely matters; the honeydew does, because the sooty mold that grows on it blackens the leaves, the trunks, and whatever is parked underneath. Lady beetles and lacewings normally end it, which is exactly why broad-spectrum spraying makes a crape myrtle worse. If a tree overhangs a patio or a driveway, this is the reason - and a reason to site the next one elsewhere.

Powdery mildew is a fungal disease that coats leaves - and often stems, buds, and fruit - in a white-to-gray powder that looks like spilled talcum. It is not one fungus but a large family of them, each fairly specialised to its own group of plants, which is why mildew on one crop rarely jumps to an unrelated one beside it. Unlike most leaf diseases it does not need wet leaves: it thrives on warm dry days followed by humid nights, and it takes hold fastest where plants stand crowded in still air or in shade. The coating blocks light, so heavily covered leaves yellow, brown, and drop early. On many plants that is mostly disfiguring and arrives late enough not to matter; where it strips away the leaves a crop still needed to finish, it costs you size, sweetness, and quality.

Watch for: Round white powdery spots on the upper leaf surfaces that spread and merge until whole leaves look dusted. It usually starts on the oldest, lowest, most shaded leaves and works upward, so check there first. Look at the undersides too, and at stems, buds, and flower stalks, which get coated as it advances. Leaves that yellow, brown, curl, or go crisp and drop early under the coating. New growth that opens small, crumpled, or twisted where the fungus has reached the shoot tips. On plants where it gets onto the fruit, a dull gray film, russeted or scarred skin, and cracking. Late in the season, tiny dark specks scattered through the white felt - that is the fungus setting up to overwinter on the debris.

Prevent: Give plants room. Crowding and still air are the biggest single driver, so space at the full recommended distance, thin seedlings properly, and divide or prune out congested growth until air moves through the plant. Full sun and an open position help; deep shade and a still corner against a wall are where it always starts. Water at the base rather than overhead, and water early in the day so nothing stays damp overnight. Keep plants evenly watered - drought stress at the roots leaves them far more susceptible, even though the fungus itself likes dry air. Go easy on nitrogen, since soft lush growth is the most vulnerable. Where resistant varieties exist for what you are growing, choosing one is the single most effective thing you can do on a plant that mildews every year. Clear infected leaves and stems away at the end of the season rather than composting them.

Treat: Start early: sprays protect healthy tissue, they do not clean up leaves that are already coated. Pick off and bin the worst leaves as soon as you see them, and open the plant up by thinning or pruning so air moves through. On anything that regrows quickly, shearing the whole plant back forces a clean flush and beats spraying. If it keeps spreading, potassium bicarbonate, horticultural oil, or neem applied weekly will hold it - cover both leaf surfaces. Sulfur also works, but it burns the foliage of some plants, should never go on in heat, and must not be mixed with or applied close behind an oil spray. Whatever you use must be labeled for the plant you are treating: follow that label and observe its pre-harvest interval on anything you eat. Do not compost badly infected material. Late-season mildew on a plant that is finishing anyway is usually cosmetic; on a crop still filling out it is worth acting on.

The historic problem of this plant, and the reason the modern hybrids exist - the US National Arboretum crossed L. indica with Japanese L. fauriei to breed it out. Here it attacks the newest shoots and the flower buds, so it costs bloom rather than just looking bad, and it is worst in shade and still air in spring and fall. An L. fauriei hybrid in full sun with air movement solves it permanently; spraying an old cultivar in a shady corner never does.

A fungal leaf spot (Cercospora lythracearum) that is the commonest late-season disease of crape myrtle in the humid South. Warm, wet weather from midsummer onward drives it, and it starts on the shaded lower and inner leaves and works upward. Heavily spotted leaves turn yellow, then orange-red, and drop, so a badly affected tree can be largely bare by early autumn - alarming to look at, and largely cosmetic, since it arrives after flowering and this plant blooms on new growth, so next year's flowers are never at stake. Older L. indica cultivars in still, shaded positions suffer most.

Watch for: Dark brown to purple-bordered spots, roughly a quarter inch across, on leaves from midsummer onward, beginning on the lowest and most shaded foliage. Leaves around the spots turning yellow and then vivid orange-red - an early, patchy version of fall colour arriving in August. Progressive defoliation from the bottom of the plant upward through late summer and early fall. Worse years following wet, warm summers, and worse in crowded plantings with poor air movement.

Prevent: Choose resistant cultivars - the L. indica x fauriei hybrids are markedly better than older L. indica types - and plant in full sun with room for air to move through. Rake up and remove fallen leaves in autumn, because the fungus overwinters in leaf litter and that cleanup is the cheapest control available. Water at the base rather than overhead, thin crowded interior growth in late winter, and avoid heavy nitrogen, which produces the soft growth the fungus prefers.

Treat: Usually nothing is needed. Defoliation in late summer looks dramatic but arrives after flowering, and an established tree refoliates normally the following spring. Sanitation - clearing fallen leaves - handles most of it. Where a susceptible cultivar defoliates severely every single year, a labelled fungicide programme begun early in the season can protect the foliage, but replanting with a resistant hybrid is the more sensible answer than an annual spray schedule.

Kept on its own slug rather than the shared cercospora record because this is a different pathogen from the one that spots hydrangeas and beets, and its management here is cultivar choice plus fall leaf cleanup.