Q. I have a large planting of 'Emerald 'n Gold' euonymus (Euonymus fortunei). A few of the plants have swollen, fleshy "tumors" around some of the stems. What are they and will they harm the plants? The plants look fine except for these growths. Will this spread to the other plants?
A. Your description matches a common disease of euonymus known as crown gall, which is caused by the bacterium Agrobacterium tumefaciens. It is characterized by the growth of galls (tumor-like swellings) on roots and/or stems, generally at the soil line. More than 90 families of woody and herbaceous plants are susceptible to infection with crown gall, including apple, pear, stone fruits (peach, cherry and plum), rose, grape, willow, chrysanthemum and sunflower.
Young galls are smooth and greenish-white to tan. As they mature, galls become dark, hard and woody. They eventually crack and decay. They are a solid mass of tissue all the way through, unlike galls caused by insects and mites.
Crown gall can kill severely infested plants, and the stunted growth and stem dieback detracts from their ornamental value. Gall formation interferes with the movement of water and nutrients between roots and leaves. The severity of the disease depends on the size, number and location of the galls. Those at the crowns of young plants cause the greatest damage and can eventually kill them. It may have little noticeable effect on older, established plants.
It seems that your plants are not severely affected yet, and there are steps you can take to help them. There is no chemical control for this disease once plants are infected. Prune out the galls and dispose of them with the trash or burn them. Disinfect your pruners between cuts by soaking them in 70 percent rubbing alcohol for five minutes and allowing them to air-dry.
Be sure to care for the infested plants well so that other stresses do not allow the galls to get the upper hand. 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 enters the plant. Severely infested plants should be removed. Do not replace them with crown gall-susceptible plants. The bacteria can spread to unaffected plants; it can persist for two years or more, even in the absence of susceptible plants.
Fortunately, there are species that are resistant to crown gall that you may be able to work into your planting. These include: boxwood (Buxus spp.); deutzia (Deutzia spp.); holly (Ilex spp.); doghobble (Leucothoe spp.) and Japanese pieris (Pieris japonica).
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