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Crown Gall

Crown galls are
common on Euonymus

By: Sandy Feather ©2009
Penn State Cooperative Extension

Sandy's Gardening Columns

  
Q: I have a large planting of ‘Emerald n’ Gold’ euonymus (Euonymus fortunei ‘Emerald n’ Gold’). A few of the plants have swollen, fleshy growths around their stems which look like brains. This can't be normal, so should I be concerned about them? The euonymus plants seem to be growing well except for these 'brainy-looking' growths.
  

 

A: From your description, it sounds as if your euonymus plants are infested with crown gall, which is a bacterial disease caused by an organism known as Agrobacterium tumefaciens. This soil-borne disease enters susceptible plants through wounds, including those caused by mechanical damage, pruning cuts, insect damage or even winter injury. This disease is characterized by the growth of galls (tumor-like swellings) on roots and/or stems, generally at the soil line. Many species of woody and herbaceous plants are susceptible to infection with crown gall.


Susceptible Plants

Stone fruit trees such as cherry, peach and plum are susceptible, along with related ornamentals. Brambles, grapes, roses, willows and euonymus are also affected.

‘Emerald n’ Gold’ is a cultivar of wintercreeper euonymus, which is particularly susceptible. Young galls are smooth and greenish-white to tan.  As they mature, galls become dark, hard and woody; they eventually crack and decay. Crown galls are a solid mass of tissue all the way through, unlike insect galls.

Emerald n' Gold Euonymus
Emerald n' Gold Euonymus

Plants suffering from crown gall often exhibit stem dieback and stunted growth, because the galls disrupt the movement of water and nutrients between roots and leaves. This certainly detracts from their ornamental value, and severely infested plants may die.

The severity of the disease depends on the size, number, and location of the galls. Galls at the crown of young plants cause the greatest damage, and can eventually kill them. Crown gall may have little noticeable effect on older, established plants.

It sounds like your plants are not severely affected yet, and there are steps you can take to keep them growing well. There is no chemical control for this disease. Agrobacterium radiobactor, a related bacterium that is antagonistic to Agrobacterium tumefaciens, is used to treat crown gall, but it is really meant for propagation nurseries rather than home gardeners. Be sure to care for the infested plants well so that other stresses do not allow the galls to overwhelm them. For example, provide supplemental water during times of drought. Avoid wounding the stems, especially near the soil line, because that is the main way the causal bacteria get into plants.

Crown gall on Euonymus
Crown gall on an older Euonymus

Severely infested plants should be removed. Do not replace them with susceptible plants. Crown gall can spread to unaffected plants since it becomes established in the soil. The bacteria can persist in the soil for two or more years, even when susceptible plants are not present on the site. If you need to prune infested plants, disinfect your pruners between cuts by dipping them in 70 percent alcohol and allowing them to air dry. If the galls are very visible and unsightly, you can try to prune them out carefully. However, crown gall is systemic; removing the galls after the fact does not get rid of the disease.

Gall-resistant varieties

Some gall resistant plants that you may be able to work into your planting include: Boxwood (Buxus spp.); deutzia (Deutzia spp.); elderberry (Sambucus spp.); holly (Ilex spp.); and doghobble (Leucothoe spp.).

Over 600 species of plants are susceptible to crown gall. Examine plants carefully before bringing them home from the nursery, and avoid those with suspicious swellings on the roots or stems. In the case of crown gall, an ounce of prevention is worth a pound of cure!


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