Rose Pest Solutions Call it Gall

The disease of roses “crown gall” has often been cited as one of the most importunate of 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 the roots.

Galls may grow two or three inches in diameter, occasionally larger. Ordinarily they are quite soft having neither a bark like surface nor a woody interior, the structure being more like an over-grown callus.

The Look of Rose Gall

If actively growing, they have a whitish or light amber color inside; when deteriorating they become brown or black. 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 main roots at the base of the plant, and mass infection of the roots may cause the stunting. Small galls or a few out on the roots seldom make much difference in the growth of a rose bush.

gall on rose

Galls forming on the canes seldom produce stunting, this type of lesion is rare outside of greenhouses or very humid and damp climates. They almost never occur in the commercial field production of roses. Crown gall is world-wide in distribution and is classed as a bacterial disease.

Gall First Reported in 1853

It is one of the earliest studied of the 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 a host 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 also where 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 made have included inoculation of tomato, kalanchoe, and certain other plants. With these “the galls failed to develop much, if any, above 83° Fahrenheit although plants and bacteria do well at higher temperatures.”

Crown Gall a Baffling Plant Disease

Crown gall still is one of the most baffling of plant diseases. Indication that 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 (tomato, sunflower, Paris-daisy, marigold), and with these it seldom is a normal disease, but has been produced artificially by inoculation. In some there have been secondary galls, and these have ceased development after something killed the bacteria.

Added to the puzzle is the record that with nearly two thousand apple trees, the infected trees after six and 25 years were not significantly smaller than the noninfected trees. It has also been reported that alkaline soils encourage crown gall and that acidifying the soil with sulfur reduced infection. Yet severe amounts of the disease have been observed in roses grown in very acid soils.

Possibly unreported as yet is the fact 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 also should have shown the disease.

Experiments indicate infested soil may not account for much spread of the disease. 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 failure of much gall formation on the untreated cuttings discounted the benefit of the chemicals. lt was concluded at that time that healthy plants may be grown even in locations known to have had crown gall previously. Another experiment was made in an attempt to infest a rose bed area with crown gall which subsequently was to be treated chemically to kill the bacteria in the soil before replanting.

Thirty bushes having crown gall were selected and planted in the bed; just across the walkway a similar bed was planted with healthy bushes of the same variety for a check. During 2 year period the bushes planted with gall outgrew the ones in the check bed with no loss of plants noted because of the gall.

At the end of the second year the galled bushes were dug and examined, 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 and in the four years following no bushes have died from 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 to plant infected bushes nor to encourage the tolerance of such in the nursery trade. It still is important to begin with inspected and healthy bushes. If crown gall then develops it might help to try a chemical treatment. 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 take into account 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. 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, 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 outting. 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. There are indications that factors as simple as aeration and drainage may have much to do with whether or not there is crown gall.

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