Rose Gall: Pest Solutions For Rough, Knobby, Tuberlike Growths

The disease of roses “crown gall” has often been cited as one of the most insistent rose diseases. It appears as rough, knobby, tuberlike growths either above or below ground parts of the plant.

In certain locations, it may develop on canes and roots. Galls may grow 2″ or 3″ inches in diameter, occasionally larger. Ordinarily, they are quite soft, with neither a bark-like surface nor a woody interior. The structure is more like an overgrown callus.

Rose GallPin

The Look of Rose Gall

If actively growing, the rose gall has a whitish or light amber color inside and becomes brown or black when deteriorating.

Infected bushes may be the largest and most floriferous in a field or garden, but stunting is the usual symptom where the disease is damaging.

Dwarfing of the bushes follows the girdling of the main trunk or stem near or below ground level.

It also results when the gall involves all of the primary roots at the base of the plant, and mass infection of the roots may cause stunting.

However, small galls or a few out on the roots seldom make much difference in the growth of a rose bush.

Galls forming on the canes seldom produce stunting. This type of lesion is rare outside greenhouses or in very humid and damp climates.

They rarely occur in the commercial field production of roses.

Crown gall is worldwide in distribution and is classed as a bacterial disease.

Gall Was First Reported In 1853

It is one of the earliest studies of bacterial diseases affecting ornamental plants.

Crown gall was reported first on grapes in Europe about 1853 and has since been described on hundreds of plant materials.

Fruit trees have been cited most frequently as hosts and probably have suffered the greatest economic losses.

On roses, besides the stunting under certain conditions, there is the harm or hazard of possible spread by contamination of garden or field location to affect future plantings.

However, there are instances where no injury has come from the gall development, and soil infestation or contamination was minor in importance.

A most excellent general review of the disease and its action is given in the Yearbook of Agriculture by the USDA.

Studies have included inoculation of tomatoes, kalanchoes, and certain other plants.

With these, “the galls failed to develop much, if any, above 83° degrees Fahrenheit although plants and bacteria do well at higher temperatures.”

Crown Gall A Baffling Plant Disease

Crown gall still is one of the most bafflings of plant diseases.

An indication that the growth of galls may continue even after the bacteria are killed has been demonstrated with inoculated periwinkle plants.

Movement of the bacteria inside stems has been proved with only a few plants, including:

  •  tomato
  • sunflower
  • Paris-daisy
  • marigold

With these, it seldom is a normal disease but has been produced artificially by inoculation.

Some have been secondary galls, and these have ceased development after something killed the bacteria.

Added to the puzzle is the record that, after nearly 2000 apple trees, the infected trees were not significantly smaller after 6 and 25 years than the non-infected trees.

It has also been reported that alkaline soils encourage crown gall, and acidifying soil with sulfur reduces infection.

Yet severe amounts of the disease have been observed in roses grown in very acid soils.

Possibly unreported as yet is that while most evidence indicates gall formation only at places of pruning cuts or other injuries, much gall development has been seen on seedling-grown roses at the origin of the primary roots where no pruning or other artificial wounding occurred.

These were much dwarfed and seriously damaged involving at least 70% percent of the bushes in the particular location.

lt might be said the galls on the seedling roses were initiated at places of injury by nematodes or some soil-borne insect.

Still, if this were so, other parts of the roots should have shown the disease.

Experiments indicate that infested soil may not account for much spread of the disease.

For example, almost 60 years ago, an area was cleared in a field of roses where more than 80 percent had crown gall.

The area was replanted the next day with rose understock cuttings set in the same rows where the infected bushes had been.

When these were budded and had grown into bushes, they were dug up and examined a year later and found to have only 10% percent gall out of 337 bushes grown from untreated cuttings.

Chemical Treatments And Solutions

A number of chemical treatments of cuttings were included in the experiment, but the failure of much gall formation on the untreated cuttings discounted the benefit of the chemicals.

It was concluded that healthy plants might be grown even in locations known to have had crown gall previously.

Another experiment was done to infest a rose bed area with crown gall, which was subsequently treated chemically to kill the bacteria in the soil before replanting.

Related: Learn To Control Powdery Mildew On Roses With Milk

Thirty bushes having crown gall were selected and planted in the bed.

A similar bed was planted with healthy bushes of the same variety across the walkway for a check.

During 2 years, the bushes planted with gall outgrew the ones in the check bed with no loss of plants noted because of the gall.

The galled bushes were dug and examined at the end of the second year. Only three showed any degree of active gall.

The rest had evidence of deteriorated galls. Twelve bushes dug from the check bed were examined and found to have become infected with root-knot nematode, accounting for the stunting there.

Replanting was done with healthy bushes; in the 4 years following, no bushes died from the crown gall.

Growth has been excellent in the bed, which previously held galled bushes.

While this information tends to minimize the importance of crown gall disease, it is not advocated plant infected bushes nor to encourage the tolerance of such in the nursery trade.

It still is important, to begin with, to inspect healthy bushes.

If crown gall then develops, it might help to try a chemical treatment.

However, inconsistent results or lack of proof that the chemical used was the cause of control makes it difficult to say how much good is done by such treatments.

Galls Originate At The Nursery?

With present knowledge, we should consider that galls occurring on the roots probably do not originate in the nursery except in the few instances where transplanting of rooted understock is a practice in field propagation.

Therefore, when galls are found on the roots, there must be some condition existing in the rose garden, which is the cause proving it is not the fault of the nursery from whom the bushes were obtained.

The same is true for galls found in aerial positions on the branches. So it is improbable that the disease originated in the nursery.

The cases where the nursery propagation might be blamed are where the galls appear on the shank of the bush, which is the original understock outing.

Since infected bushes can grow and give good results, experience has shown bushes in a garden planting can be kept on growing without necessarily harming the rest of the garden, even with some having crown gall.

Until there is a stunting of the bushes, it probably would not pay to resort to chemical treatment and replanting.

However, there are indications that factors as simple as aeration and drainage may have much to do with whether or not there is a crown gall.