Pest Management Office 491 College Avenue Orono, ME 04473-1295 |
Introduction
Crown Gall is a common disease of many woody shrubs and some herbaceous plants. It is caused by the bacterium Agrobacterium tumefaciens which can infect 140 genera in over 90 families of plants. It is especially common in the rose family. The Agrobacteria have been extensively studied over the last 80 years. They are useful today in the genetic engineering of plants because of their ability to integrate parts of their own DNA into a plant's genome. In nature this ability allows the transformation of normal plant cells into tumor cells.
Symptoms
As the name implies, galls tend to form on the stem at the soil line. However, galls may also form on the roots or on above ground stems and twigs. The galls are rough, hard and woody when older; young galls may be smooth and somewhat spongy. Unlike insect galls, these galls are solid throughout. They vary in size from very small to over an inch in diameter. Infected plants may be stunted and lack vigor because of the disrupted flow of water and nutrients from the roots.
Survival and Dispersal
Crown gall bacteria enter the plant through wounds. Soon after infection the bacteria induce the plant cells to proliferate and also to produce unusual chemicals (opines) which the bacteria use as an energy source. Outward symptoms may not develop for several weeks depending on temperature, humidity and the growth of the plant. As the gall increases in size its ability to obtain nutrients decreases and finally growth stops. The gall begins to decay releasing bacteria into the soil. Bacteria will remain active in the soil for a minimum of two years in the absence of a host or longer on decaying infected tissues. The bacteria are spread by any means that can move infested soil such as cultivation equipment, shoes, runoff, splashing soil, etc. Commonly the disease is moved on infected nursery stock. Chewing insects may also carry bacteria to healthy plants.
Management
1) Avoid all unnecessary wounding 2) When grafting use sterilized tools 3) Inspect plants carefully when buying 4) Remove and burn infected plants 5) Plant resistant plants in infested areas 6) Rotate into non-susceptible crops (cowpeas, oats, corn, crotalaria, grass crops) for 2-4 years 7) Painting galls with the chemical eradicant Gallex may be effective 8) Use the antagonistic bacterium Agrobacterium radiobacter (Galltrol) as a pre-planting preventative treatment.
When Using
Pesticides Bruce A. Watt, Extension Plant
Pathologist Where trade names are used, no
discrimination is intended and no endorsement by Cooperative |
PEST MANAGEMENT OFFICE | UMCE HOMEPAGE | UMAINE
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