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Crown gall - a root swelling that enfeebles plants.

Crown gall--a root swelling that enfeebles plants

Often lethal, always enfeebling, crown gall can occur wherever plants are grown. The disease is caused by a soil-dwelling microbe called Agrobacterium tumefaciens; it enters plant tissue through any sort of wound. Infection results in swellings (galls) on roots, or on the crown where trunk and roots join.

While galls on plant crowns are visible (as shown above right), you can't be certain whether galls are growing on roots unless you dig up the plant (above left). Often the only sign that a plant is infected is feeble growth or actual decline.

Galls are woody at first, later spongy or corky in appearance. They can become pea-size to basketaball-size, interfering with the transfer of nutrients. Most garden plants are susceptible, including most deciduous fruit trees and other members of the rose family.

Don't confuse crown gall with clumsy graft unions, which may make swellings but don't show notable changes in color or texture. Root nematode damage can also resemble crown gall, but the swellings are usually smaller and more numerous.

Prevent its spread. Galls often appear at the point where grafting or budding is done--and the disease is frequently transmitted by tainted tools. If crown gall has appeared in your garden, keep budding knives, grafting tools, and pruning tools clean; sterilize between cuts by dipping them in methyl alcohol or a solution of 1 part sodium hypochlorite (household bleach) to 10 parts water.

Root wounds that invite infection can be caused by insect or nematode feeding or by mechanical damage--digging, cultivating, or root-pruning in the nursery or by the gardener before planting.

Infected nursery stock was once the source of most crown gall, but now nurseries take great pains to offer clean stock. Still, even a healthy plant can become diseased if you put it in infected soil. If you have an infected plant that is productive, keep it; galls on crowns can be cut off, but they almost always recur. Pull and destroy young plants that are infected. Do not replant in the same site for several years.

Photo: Unearthed cherry tree has galls at root ends. Infection occurred when roots were cut, during digging or root-pruning

Photo: At soil level, blackish-brown, corky mass near rose's base indicates that infection took place at or near the bud union
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Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Date:Apr 1, 1986
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