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Crown gall is a common plant disease caused by the soil-borne bacterium Agrobacterium tumefaciens. It is found throughout the world and occurs on woody shrubs and herbaceous plants including grapes, raspberries, blackberries and roses.

Crown gall symptoms include round, wart-like growths — 2 inches or larger in diameter — that appear at or just above the soil line, or on lower branches and stems. Plants with several galls may be unable to move water and nutrients up the trunk and become weakened, stunted and unproductive. Young plants can be killed by developing gall tissue.

The bacteria responsible for crown gall can persist in the soil for many years and are released when galls become saturated with moisture or as older galls decompose. Susceptible plants are infected through fresh wounds or abrasions, many of which are a result of pruning, freeze injury, soil insects, cultivation and other factors that may damage plants. Nursery stock is often infected through grafting and budding scars.

Treatment

  1. Select resistant cultivars when possible and purchase plants from a reputable nursery.
  2. Do not buy plants that shows signs of swelling or galling.
  3. When caring for susceptible plants, avoid injury or pruning wounds that may come in contact with the soil.
  4. Use Tree Wrap to protect against string trimmer damage and keep your garden tools clean.
  5. Provide winter protection with natural burlap so bark does not crack.
  6. In many cases, existing galls can be removed with a sharp pruning knife. Destroy the infected plant tissue and treat the wound with pruning sealer. If the plant does not recover, remove and destroy it.

Tip: To get rid of this problem on roses, remove the infested plant and prune out gall tissue. Soak the entire root system and damaged areas for 15 minutes in a solution of 2 level Tbsp of Actinovate per 2-1/2 gallons of water. Replant in healthy soil and apply 1/2 Tbsp per 2-1/2 gallons of water as a foliar spray at weekly intervals.

Reduce the incidence of crown gall by planting noninfected “clean” trees. For seedling rootstocks, nurseries should collect the seed so it never contacts the soil where the Agrobacterium resides. Before planting, make sure trees stay moist and the roots do not dry out. It is also important to carefully handle trees to avoid injury as much as possible, both at planting and during the life of the tree in the orchard. Although preplant preventive dips or sprays with a biological control agent are available, their effectiveness can be variable on walnut trees. Strains of Agrobacterium tumefaciens (formerly A. radiobacter) strain K-84 are available as commercial products. However, it is effective only as a preventive treatment and does not eradicate galls. Use as a root dip or spray before heeling in (covering with moist soil until trees are planted) or planting.

Look for and manage crown gall during the growing season when the orchard is not wet because moisture favors the bacterium. When established orchard trees are infected with crown gall, you can use a combination of surgery, flaming, or a bactericide to treat the tumors. The best time to treat is in the spring or early summer because with rapid tree growth occurring, new callous tissue is formed relatively quickly.

Management is most effective for small galls on young trees. The procedure, however, can be expensive and difficult to carry out, depending on the size and location of the galls.

  • It is always best to remove galls when they are small. Usually by the time they’re seen at ground level, there may be extensive galling on crown area beneath soil.Only treat trees that are vigorous. Stunted trees should be removed.
  • If trees less than 4 years old are severely affected with galls, it is more economical to remove the trees and replant.
  • Treatment may be effective on older trees. The decision whether to treat galls or remove trees depends on tree vigor, the severity of galling, and the cost of treatment relative to the cost of replacing trees.

To treat crown galls:

  1. First remove soil away from the crown and roots to completely expose the gall. Soil can be safely removed using pneumatic equipment such as air compressors. Because no water is used, treatment can be done immediately after removal.
  2. To flame the gall, use a propane cylinder or bottle and slowly move the torch tip around the margin of the gall, creating a red-hot zone that is about 1 inch wide. It is advantageous to surgically remove the main part of gall in order to gain access to all parts of the gall margin. If surgery is used, be sure to sterilize the tools with heat before advancing to the next tree. Flaming should never be used on very young trees.
  3. As an alternative to flaming, galls can be treated with a bactericide such as Gallex, but treatment success is dependent upon complete removal of the gall first and then applying the treatment.
  4. Leave the treated areas uncovered for the summer and re-treat if galls begin to regrow. Treatment success is about 80%.

When replanting a previously affected site:

  • Remove as many of the old tree roots as possible.
  • Grow a grass rotation crop to help degrade leftover host material and reduce pathogen levels.
  • Fumigate with Telone C35.
  • Consider rootstock’s resistance (PDF). Clonal ParadoxRX1 has moderate resistance to crown gall. Clonal Paradox Vlach and VX211 have low resistance to crown gall. Although seedling black rootstock is not as susceptible to crown gall as seedling Paradox, walnut varieties on black rootstock generally aren’t as vigorous so should be planted on loamy soils.
  • Offset the new trees from the previous tree spacing to minimize contact of healthy new roots with any infested roots and soil that may remain.
  • Keep the crown area dry to help reduce disease severity.

Crown gall

Crown gall, plant disease, caused by the bacterium Agrobacterium tumefaciens (synonym Rhizobium radiobacter). Thousands of plant species are susceptible. They include especially grape, members of the rose family (Rosaceae), shade and nut trees, many shrubs and vines, and perennial garden plants. Symptoms include roundish rough-surfaced galls (woody tumourlike growths), several centimetres or more in diameter, usually at or near the soil line, on a graft site or bud union, or on roots and lower stems. The galls are at first cream-coloured or greenish and later turn brown or black. As the disease progresses, plants lose vigour and may eventually die.

crown gallPlant infected with crown gall.Bhai

Crown gall can be avoided by using nursery stock free of suspicious bumps near the crown, former soil line, or graft union; practicing five-year rotation or avoiding replanting for that period; removing severely infected plants (including as many roots as possible); protecting against injury; keeping down weeds; controlling root-chewing insects and nematodes; cutting away large galls on trees; and disinfecting wounds.

By: Kevin Ong and Ashley Brake

Crown gall, a bacterial disease that occurs throughout the world, infects several different plant hosts. In particular, it is a devastating disease in the Rosaceae (rose) family.

The specific bacterium, Agrobacterium tumefaciens, causes crown gall by inserting a tumor-inducing gene into the plant genome. Scientists have extensively studied this bacterium and used it for introducing desirable traits into many cultivated plant species. Since the 1970s, genetic engineers have exploited the bacteria’s ability to insert genes into other plants, and the agricultural industry has benefitted from creating genetically modified plants with crops that grow faster and bigger and are resistant to insects and other diseases.

Symptoms

Initial symptoms on roses appear as a small, light green spherical swelling around the crown of the plant. This swelling also occurs below the soil line (Fig. 1) on the roots as well as on higher branches, depending on the infection site. These growths should not be confused with normal callus growths that commonly form at wound and grafting sites.

Once the infection worsens, the shape of the galls becomes uneven, and they harden into a dark, woody mass (Fig. 2). In heavily infected plants, secondary tumors may develop near the first gall. There may be several tumors affecting a single plant in any given infection. Gall formation interferes with the plant’s ability to transport water and food supplies, producing other symptoms such as

  • Weakness
  • Stunting
  • Discoloration of leaves
  • Dieback of shoots
  • Increased susceptibility to winter injury or secondary infection
  • Wilt and, eventually in severe infections, death

It is easy to confuse crown gall with symptoms of hairy root, another root pathogen caused by the bacterium Agrobacterium rhizogenes. Hairy root causes the same gall formations; however, they are not woody and produce fibrous roots that project from the galls, giving them a “hairy” look.

Cause

The bacterium that causes crown gall lives in the soil that surrounds the host—in this case, roses. This bacterium can live in the soil as a decomposer for years without infecting a living host. When a plant is injured—either by mechanical transmission, insect feeding, or naturally—the damaged cells release compounds into the soil, attracting the bacterium to the wound site. Once inside, the bacterium replicates rapidly, forming the tumor-like gall by integrating some of its DNA (deoxyribonucleic acid), which is contained in a circular plasmid, into the host’s DNA. A plasmid is a small DNA molecule that is isolated from chromosomal DNA and can replicate on its own. Once the bacterial genomic material is incorporated into the host’s genome, the normal plant cells are altered. They multiply and form the gall structure.

Only the strains of these bacteria that contain these tumor-inducing plasmids (Ti plasmid) can cause disease. Some strains of A. tumefaciens lack the specific plasmid and remain in the soil without causing disease. When the outside tumor cells shed into the soil, replicated bacteria can live in the soil and be carried off by water to infect neighboring plants.

Environmental Factors

A.tumefaciens lives primarily in the upper layers of the soil closest to the plant (rhizosphere). It lives for years off of decaying organisms until conducive conditions allow it to inhabit a host plant. The bacterium can enter a plant only through a wound site or natural opening. Following favorable rose-growth conditions, A. tumefaciens becomes dormant during the cold winter months and is most active in summer months.

Managing crown gall disease includes, but is not limited to, these preventive cultural practices:

  • Purchase healthy-looking plants.
  • Avoid injuring the plant (especially around the roots and crown) while planting, and try to reduce the impact of chewing insects that can cause wounds.
  • Plant in soils with no previous record of crown gall.
  • Sterilize all pruning utensils before and after use.
  • If symptoms develop after planting, dig up the whole plant and dispose of it properly, including the surrounding soil.
  • Use insecticides to reduce the wounds on plant tissues that insects can cause. Be careful when undertaking any chemical control measures.
  • Soak seeds or bare-rooted plants in a solution containing a closely related species, Agrobacterium radiobacter, as a preventive treatment. The bacterium
  • A. radiobacter does not induce disease in plants; it uses similar resources and can prevent crown gall disease by typically out-competing A. tumefaciens.

Sources

Londeree, N. 2013. Garden Bad Guys–Crown Gall.Marin Rose Society. ttp://www.marinrose.org/crowngall.html.

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Euonymus with a case of crown gall

Overview crown gall

Crown gall causes round galls to form on stems or roots, often near the soil line of the plant. Galls may vary from the size of peas to over an inch in diameter. When young, the galls can be white or cream colored and spongy or wart-like; as they age, they become dark and woody. Galls can interfere with the plant’s ability to move water and nutrients through the stem, which may result in stunting or decline of the plant. Crown gall can infect nearly all dicotyledonous plants and is most common in euonymus, Prunus spp., brambles, rose, willow, grapes, and many other plants.

Signs and symptoms of crown gall

The crown gall bacterium, Agrobacterium tumefaciens, enters the plant through a wound. It then inserts a portion of its DNA into the DNA of the plant. Once this bacterial DNA is incorporated into the plant DNA, it induces the plant to overproduce plant hormones that stimulate cell division, resulting in a gall that is a perfect home for the bacterium. The bacterial DNA also causes the plant to produce special food called opines that only Agrobacterium can utilize.

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant and Insect Diagnostic Clinic can help you to investigate and confirm (through testing) if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. If your sample is from outside of Iowa, please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us. For contact information for other diagnostic laboratories in U.S. states, visit the

Management of crown gall

Crown gall is usually introduced into a location on infected planting stock, so it is crucial to buy only disease-free plants. Inspect plant root system before transplanting in the garden.

Avoid unnecessary wounding to prevent infection. If galls are present, they cannot be cured, and the plant should be removed. Once crown gall is introduced to a site, the bacteria can remain in the soil for many years.

Practice good sanitation: cleaning tools, pots, and other tools an surfaces, treat them with a disinfectant (rubbing alcohol or diluted bleach).

No chemical sprays are effective against crown gall, but a biocontrol agent made from the bacterium Agrobacterium radiobacter can be used as a dip for propagative cuttings to prevent infection by the crown gall bacterium. This biocontrol is marketed as Galltrol A, Norbac 84C, Nogall, or Diegall. Keep in mind when using biocontrol agents, you are trying to introduce and establish a biocontrol organism in the field onto a very rich soil ecosystem, where a lot of microbial competition can impact the efficacy of this method.

Plants Affected By Crown Gall: Tips On How To Fix Crown Gall

Before you decide to start crown gall treatment, consider the value of the plant you are treating. The bacteria that causes crown gall disease in plants persists in the soil as long as there are susceptible plants in the area. To eliminate the bacteria and prevent the spread, it’s best to remove and destroy diseased plants.

What is Crown Gall?

When learning about crown gall treatment, it helps to know more about what is crown gall in the first place. Plants with crown gall have swollen knots, called galls, near the crown and sometimes on the roots and twigs as well. The galls are tan in color and may be spongy in texture at first, but they eventually harden and turn dark brown or black. As the disease progresses, the galls can totally encircle the trunks and branches, cutting off the flow of sap that nourishes the plant.

The galls are caused by a bacterium (Rhizobium radiobacter formerly Agrobacterium tumefaciens) that lives in the soil and enters the plant through injuries. Once inside the plant, the bacterium injects some of its genetic material into the host’s cells, causing it to produce hormones that stimulate small areas of rapid growth.

How to Fix Crown Gall

Unfortunately, the best course of action for plants affected by crown gall is to remove and destroy the infected plant. The bacteria can persist in the soil for two years after the plant is gone, so avoid planting any other susceptible plants in the area until the bacteria dies out for lack of a host plant.

Prevention is an essential aspect of dealing with crown gall. Inspect plants carefully before you buy them, and reject any plants with swollen knots. The disease can enter the plant in the nursery through the graft union, so pay particular attention to this area.

To prevent the bacteria from entering the plant once you get it home, avoid wounds near the ground as much as possible. Use string trimmers with care and mow the lawn so that debris flies away from susceptible plants.

Galltrol is a product that contains a bacterium that competes with Rhizobium radiobacter and prevents it from entering wounds. A chemical eradicant called Gallex may also help prevent the crown gall disease in plants. Although these products are sometimes recommended for crown gall treatment, they are more effective when used as a preventative before the bacteria infects the plant.

Plants Affected by Crown Gall

Over 600 different plants are affected by crown gall, including these common landscape plants:

  • Fruit trees, particularly apples and members of the Prunus family, which includes cherries and plums
  • Roses and members of the rose family
  • Raspberries and blackberries
  • Willow trees
  • Wisteria

Plant galls

DESCRIPTION

Galls are abnormal growths that occur on leaves, twigs, roots, or flowers of many plants. Most galls are caused by irritation and/or stimulation of plant cells due to feeding or egg-laying by insects such as aphids, midges, wasps, or mites. Some galls are the result of infections by bacteria, fungi, or nematodes and are difficult to tell apart from insect-caused galls. Seeing the insect or its eggs may help you tell an insect gall from a gall caused by other organisms.

In general, galls provide a home for the insect, where it can feed, lay eggs, and develop. Each type of gall-producer is specific to a particular kind of plant.

Galls may appear as balls, knobs, lumps, or warts, each being characteristic of the causal organism. In addition to the unusual structure of galls, they draw attention due to their range of colors: red, green, yellow, or black. Factors such as weather, plant susceptibility, and pest populations affect the occurence of galls on plants from year to year. Oaks are one of the most susceptible, being host to over 500 different wasps, aphids, mites, and midges that cause galls on leaves and twigs.

Plant gall damage is usually an aesthetic problem and is not considered serious. Affected trees ordinarily show little injury, although foliage of young trees is sometimes completely deformed. On ornamental trees this condition can be unsightly.

COMMON GALLS

One familiar plant gall is the maple bladder-gall often seen as bright red bead-like growths on upper leaf surfaces of silver and red maple. The causal agent is an eriophyid mite. The mites feed inside these galls. The galls are green at first. Later they turn a reddish color and by the end of summer they may be almost black. By fall, the mites have left the foliage to overwinter on the twigs, usually at the bases of the buds.

Oak apple gall, caused by several species of gall wasp, consists of large, dry galls attached to the midrib or petiole of a leaf. As the galls mature they become papery. The single larva in each “apple” is inside a small and very hard seedlike cell.

Horned oak gall appears on red and pin oaks and is also caused by a wasp (Callirhytis cornigera). Small, blister-like, oblong leaf galls appear along veins on undersides of leaves. They turn into dark brown, spherical twig galls. The horns develop the second or third year after the wasp’s eggs are laid and the larvae inside are nearing their full size.

Crown gall is one of the most studied plant diseases. The disease is caused by a soil-inhabiting bacterium (Agrobacterium tumefaciens). More than 600 plant species in over 90 plant families are susceptible to this disease, although relatively few species sustain significant damage. Galls form on roots and stems, especially at the root collar – the junction of roots and stem. Young plants with large or numerous galls tend to be stunted and predisposed to drought damage or winter injury. Galls continue to enlarge as plants grow and can disfigure woody stems.

MANAGEMENT

Fortunately, galls, while unusual and sometimes even alarming in appearance, cause little permanent injury and seldom result in the death of the plant. For this reason chemical sprays are rarely necessary or recommended to treat gall infestations.

By the time the galls become noticeable, the insect or mite causing the injury is protected from chemical sprays. If only a few galls are present, the affected part of the plant may be removed.

Crown gall

How to manage crown gall

Crown gall on bare root transplants

Preventing crown gall

Prevention is the best method of control because once established in an area, the crown gall bacteria can be very difficult to eliminate.

  • Check all new plants carefully.

  • Do not plant any tree or shrub with galls on the roots or stems.

  • Pay extra attention when planting roses, fruit trees, poplar or willows.

The biological control bacteria Agrobacterium radiobacter K-84 can be used to protect trees and shrubs from crown gall infection during planting.

  • Dip roots of bare root plants or drench potted plants with a solution of water and biological control bacteria, Agrobacterium radiobacter K-84.

  • These bacteria protect roots by producing an antibiotic.

  • They also cover wound sites that the crown gall bacteria would use to start an infection.

    • Galltrol is a commercial formulation of A. radiobacter K-84 that is registered for use in Minnesota.

If you notice crown gall on your trees and shrubs

On a recently planted tree or shrub:

  • Dig up the plant and the soil immediately around the roots and dispose of it.

  • Do not add infected plant material to compost piles.

  • Burning is the best way to dispose of infected woody plants.

On established trees and shrubs:

  • Established trees and shrubs can tolerate infection with crown gall and can be left in the landscape.

  • Make sure to disinfect pruning tools with a 10-percent solution of household bleach after using them to prune crown gall infected trees.

  • If infected plants exist on your property, avoid planting highly susceptible species like rose, willow, poplar and fruit trees.

Bacterial Crown Gall of Fruit Crops

Crown gall is caused by the bacterium Agrobacterium tumefaciens. This bacterium has the widest host range of any plant pathogen. It is capable of causing tumors, or “galls,” on virtually all plant species, except the monocots (grasses). A similar bacterium, Agrobacterium rubi, causes galls on the canes of brambles. All fruit crops grown in Ohio are susceptible. The disease is particularly destructive on brambles (raspberries and blackberries) and grapes. It can also cause severe problems on apple, pear, blueberry, all stone fruits, and on ornamentals.

Figure 1. Crown galls on raspberry root.

The bacteria induce galls or tumors on the roots, crowns, trunks, and canes of infected plants. These galls interfere with water and nutrient flow in the plants. Seriously infected plants may become weakened, stunted, and unproductive.

The disease first appears as small overgrowths or galls on the roots, crown, trunk, or canes. Galls usually develop on the crown or trunk of the plant near the soil line or underground on the roots. Above ground or aerial galls may form on canes of brambles and highly susceptible cultivars of grape. Although they can occur, aerial galls are not common on fruit trees.

In early stages of development the galls appear as tumor-like swellings that are more or less spherical, white or flesh-colored, rough, spongy (soft), and wart-like. They usually form in late spring or early summer and can be formed each season. As galls age they become dark brown to black, hard, rough, and woody. Some disintegrate with time and others may remain for the life of the plant.

The tops of infected plants may appear normal. If infection is severe, plants may be stunted, produce dry, poorly developed fruit, or show various deficiency symptoms due to impaired uptake and transport of nutrients and water.

Figure 2. Crown galls on apple branch.

Causal Organism

The crown gall bacterium is soil-borne and persists for long periods of time in the soil in plant debris. It requires a fresh wound in order to infect and initiate gall formation.

Wounds that commonly serve as infection sites are those made during pruning, machinery operations, freezing injury, growth cracks, soil insects, and any other factor that causes injury to plant tissues. Bacteria are abundant in the outer portions of primary galls, which is often sloughed off into the soil. In addition to primary galls, secondary galls may also form around other wounds and on other portions of the plant in the absence of the bacterium. The bacteria overwinter inside the plant (systemically) in galls, or in the soil. When they come in contact with wounded tissue of a susceptible host, they enter the plant and induce gall formation, thus completing the disease cycle. The bacteria are most commonly introduced into a planting site on or in planting material.

Figure 3. Crown galls on grape vine.

  1. On grapes, the double trunk system of training may be a useful system for minimizing losses due to crown gall. If one trunk is infected, it can be removed. The remaining trunk can be pruned leaving a full number of buds until the second trunk can be renewed. Galls on the upper parts of the trunk or on canes can be removed by pruning.
  2. Avoid all unnecessary root, crown, and trunk wounding by careless cultivation and other machinery operation, and control soil insects. Any practice that reduces wounding is highly beneficial. Preventing winter injury (especially on grapes) is also beneficial.
  3. Obtain clean (disease free) nursery stock from a reputable nursery and inspect the roots and crowns yourself to make sure they are free from galls. Avoid planting clean material in sites previously infested with the bacteria.
  4. A relatively new biological control agent for crown gall is available for apple, pear, stone fruit, blueberry, brambles, and many ornamentals. It is not effective on grape.
    The agent is a nonpathogenic strain of bacterium (Agrobacterium radiobacter strain 84) that protects the plants against infection by the naturally occurring strains of pathogenic bacteria in the soil. Nursery stock is dipped in a suspension of commercially prepared Agrobacterium radiobacter strain 84 at planting time. The antagonistic bacteria act only to protect disease free plants from future infection by the crown gall bacterium; they cannot cure infected plants.

This fact sheet was originally published in 2008.

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