Rose rosette disease

Rose rosette emaravirus

also called Witches broom of rose

Bright red witches-broom growth with too many thorns, spreading across North America with no cure. Dig the whole plant out, roots and all — do not try to prune it out.

Virus No cure Spread by insectsSpread by contact Spreads to neighbors

What you'll see

A shoot of intense, unnatural red that never greens up, thicker and more succulent than the growth around it.
A dense broom of many small shoots from one point, with leaves crowded and distorted.
Excessive soft thorns — far more than the cultivar should carry, sometimes covering the stem entirely.
Flower buds that are deformed, aborted or open into distorted, off-colored blooms.
Leaves narrow, strap-like and crinkled, and the whole plant declining over one or two seasons.

Why it happens

A virus carried from rose to rose by a microscopic eriophyid mite that drifts on the wind, and moved much further by grafting and by infected nursery stock. It multiplies inside the plant, so by the time a broom appears the virus is already throughout the root system — which is exactly why cutting the broom out does not work.

Spreading steadily across the United States, worst where roses are planted in quantity — municipal beds, mass plantings of landscape roses, and gardens downwind of them. The mites move on the wind in spring and summer, so a garden within a hundred meters of an infected planting is at real risk.

Treating it

There is no cure and no treatment. Dig the plant out with as much of the root as you can and bag it for the bin.
Do not prune the broom out and hope. The virus is systemic; the plant is a reservoir infecting every rose downwind of it.
Bag the plant before you carry it through the garden, so the mites do not blow off on the way.
Clean pruners with alcohol between plants, and do not use cuttings from a suspect plant.
Wait a few weeks before replanting a rose in the spot, and remove every piece of root you can find first.

Keeping it away

Space roses so their canes do not touch; the mites walk as well as blow, and touching plants share them.
Inspect new plants for excessive thorniness and red distorted growth before buying, and avoid multiflora rose entirely.
Remove wild multiflora rose from your boundary — it is the reservoir the disease came from and spreads on.
Walk the roses in spring and early summer looking for a single red broom; caught in the first month it costs you one plant instead of the bed.
Where the disease is established locally, consider planting something other than roses in a mass; it is a hard answer but an honest one.

Who gets it

All garden roses. Multiflora rose is the wild reservoir; Knock Out and other landscape roses are hit hard because they are planted in quantity.

Rose