Burning Bush

Heavily sheared hedges in still, shaded air are the classic victims. It is a good argument for removing the plant rather than for spraying it - especially since the native replacements are not hosts.

Rows of small brown, tan, black, white, or waxy bumps along stems, twigs, leaf midribs, and leaf undersides that do not brush off but can be scraped loose with a fingernail. A sticky shine on the leaves - and on the floor, table, or path beneath the plant - that later turns black with sooty mold. Ants running steadily up and down the stems, since they farm and defend scale for that honeydew; often the first sign anything is wrong. Yellowing leaves, weak thin growth, and dieback of individual branches or canes that are heavily encrusted. On fruit crops, scale covers and sooty mold directly on the fruit. Check the leaf undersides and the shaded inner wood, which is where colonies build up unseen.

Horticultural oil is the main control: it works by smothering, so it has to coat the insects thoroughly - stems, twigs, and leaf undersides - and it usually needs repeating, because the waxy covering shields them and no single pass reaches everything. On deciduous woody plants a dormant-season oil smothers the overwintering stage while the leaves are out of the way, and timing a growing-season spray to the crawler stage, when the young are mobile and uncovered, is far more effective than spraying settled adults. On a small plant or a light infestation, scrub or wipe the scales off by hand, or dab them with a cotton swab of rubbing alcohol. Prune out and destroy badly encrusted wood rather than trying to save it. Wash off the sooty mold once the scale is gone - it lives on the honeydew, not on the plant, and stops once the supply does. Anything you spray must be labeled for the plant, and oils can burn delicate foliage, so test first.

Inspect. Look over leaf undersides and stems regularly - on a crop you pick, every harvest is a scouting chance - and check every new plant thoroughly before you buy it, plant it, or set it beside anything else, because scale almost always arrives on a plant rather than flying in. Quarantine new houseplants for a few weeks. Keep plants unstressed and not over-fertilized, since soft, forced growth is what populations build on. Prune for airflow and light to open up the shaded inner growth where scale hides, and prune out heavily infested wood as routine maintenance - on anything that gets a hard annual pruning, that alone removes most of any buildup. Leave the lady beetles, lacewings, and parasitic wasps alone, since they normally keep scale down to nothing, and keep ants off the plant where you can, because ants protect the colonies from those predators. Indoors, avoid hot, dry, still winter air.

Scale insects are sap-suckers that spend most of their lives immobile, fixed to a stem, twig, or leaf underside beneath a waxy or shell-like cover. They look far more like bumps, blisters, or crusty encrustations than like insects, which is why an infestation is usually well established before anyone notices it. Soft scales excrete large amounts of sticky honeydew that drips onto everything below and grows a black sooty mold - and those blackened leaves are often the first thing a gardener actually sees. Armored scales produce no honeydew but sit under a hard shield that protects them from most sprays. They spread as tiny mobile crawlers in the weeks after hatching, which is the only stage that moves and the only stage that is easy to kill. Populations build on stressed plants, on crowded shaded growth, and above all on plants kept indoors in dry, still air over winter.

Dense, uniform, ankle-high seedlings under and downwind of a mature shrub, and in woodland interior with no other disturbance. Winged twigs on knee-high plants deep in shade. Absence of tree seedlings and spring wildflowers through the carpet.

Hand-pull seedlings and small plants in moist soil; they come out. Remove the fruiting parent shrubs to shut off the seed supply, then keep walking the site each spring for several years, since neighboring plantings will keep re-seeding you.

Do not plant it, including the dwarf and 'sterile' cultivars, and remove any existing shrub before it fruits. Pull the seedling flush every spring while it is small - an hour with a bag beats a day with a saw later.

The mechanism that makes this shrub a forest problem rather than a hedgerow weed. Burning bush seed germinates readily in full woodland shade, which most invasive shrubs cannot do, so bird-dropped seed establishes under a closed canopy far from any planting. The result is a continuous carpet of seedlings - often hundreds per square yard under and downwind of a mature shrub - that suppresses tree seedlings, spring ephemerals, and native shrubs and quietly stops the woodland regenerating.

A continuous winged-twigged shrub layer under forest canopy or along a woodland edge. Shrubs fruiting heavily in deep shade. Blazing scarlet patches visible from a distance in a woodland in October - the easiest way to map an infestation.

Dig out the root crown of small and mid-sized shrubs, or cut low and treat the fresh stump immediately with a woody-plant herbicide from late summer to leaf drop, when reserves are moving downward; basal-bark treatment of small stems works in the dormant season. Use a product whose label lists the site you are treating and follow that label - it is legally binding. Near a wetland, ditch, or streambank, an aquatic-labelled product is required, and in most states a permit or a licensed applicator as well. Cutting without treating produces a denser, multi-stemmed shrub.

Remove ornamental plantings, which are the seed source; take out the largest fruiting shrubs first; and replant with natives so the cleared ground is not simply re-invaded.

Where the seedlings grow up, burning bush forms a dense shrub layer that displaces native understory across eastern and midwestern forests, roadsides, old fields, and stream corridors. It tolerates deep shade, poor soil, drought, road salt, and deer browsing, so almost no site condition limits it, and it fruits heavily even in shade. The mature thicket casts dense summer shade of its own, and the low-value fruit it offers birds is poor substitute for the native shrubs it replaced.