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Beginner

Scientific Name
            Rhizobium vitis (formerly named Agrobacterium vitis)

Identification
Current season galls

• First apparent in early summer as swellings on the trunk
• Soft, convoluted, callus-like tissue, creamy in colour, erupting through the bark layer near injured sites of the vine
• In young vines, gall formation is often seen just above the graft union
• By late summer the galls darken and become corky in texture with a rough surface and persist for several years

After one or two years

• Dead galls may flake off the vine
• Young galls may often form at the periphery of old galls
• Typically seen from the soil line to the first wire
• Stressed infected vines are often killed during low temperature episodes in the winter

Often Confused With:
Excessive callusing of nursery stock under wet conditions: callus does not become corky and flake off.

Period of Activity
Early summer, particularly after winter injury has occurred in cold sensitive varieties.

Scouting Notes
Galls are mostly found on the lower trunk, from the soil line to the first wire; however, aerial galls may develop more than one metre up the trellis. Monitor these areas of the trunk for galls starting in early summer. Severely diseased vines usually exhibit significant reductions in yield and vigour, predisposing them to winter kill.

Threshold
There is no threshold.  Trunks with crown gall symptoms will weaken and die.  However, other symptomless trunks on the same vine, while infested, may continue to produce crop for many years.  If the gall is at the graft union and no suckers develop, the vine will die.

Advanced

Scientific Name
            Rhizobium vitis (formerly named Agrobacterium vitis )

Identification
Current season galls

• First apparent in early summer as swellings on the trunk
• Soft, convoluted, callus-like tissue, creamy in colour, erupting through the bark layer near injured sites of the vine
• In young vines, gall formation is often seen just above the graft union
• By late summer the galls darken and become corky in texture with a rough surface and persist for several years

After one or two years

• Dead galls may flake off the vine
• Young galls may often form at the periphery of old galls
• Typically seen from the soil line to the first wire
• Stressed infected vines are often killed during low temperature episodes in the winter

Often Confused With:
Excessive callusing of nursery stock under wet conditions: callus does not become corky and flake off.

Biology
The crown gall bacterium survives within galls and systematically infested vines. The bacterium remains inside the vine, without causing symptoms, until there is an injury to the trunk and only then invades the outer part of the trunk where it causes rapid cell multiplication and distortion of tissue producing galls.  The crown gall bacterium may also survive in vineyard soils in vine debris. It is believed that the majority of infections are a result of symptomless contaminated planting material. Generally, the incidence of crown gall is correlated with cold susceptibility; less cold tolerant varieties having a higher incidence of crown gall infection. 

Period of Activity
Early summer, particularly after winter injury has occurred in cold sensitive varieties.

Scouting Notes
Galls are mostly found on the lower trunk, from the soil line to the first wire; however, aerial galls may develop more than one metre up the trellis. Monitor these areas of the trunk for galls starting in early summer. Severely diseased vines usually exhibit significant reductions in yield and vigour, predisposing them to winter kill.

Threshold
There is no threshold.  Trunks with crown gall symptoms will weaken and die.  However, other symptomless trunks on the same vine, while infested, may continue to produce crop for many years.  If the gall is at the graft union and no suckers develop, the vine will die.

Management Notes
Management practices that reduce injury are important in managing this disease, since the expression of crown gall is closely correlated with the occurence of injury.

Before Planting

Losses of grape plants due to crown gall may be minimized with some considerations before vineyard site selection or planting.

• Select sites with good soil and air drainage, avoid frost-prone areas
• Select rootstocks that are resistant to crown gall such as Courderc 3309, 101-14 Mgt, and Riparia Gloire,
• Select hardy, cold tolerant varieties where possible
• Do not replant old vineyard areas where crown gall was present less than 2 years after grapevines have been removed. Crown gall bacteria can survive in the remnants of the old grape plants until the debris decomposes. When removing diseased vines, remove as much of the root system as possible.
• Purchase vines from a reputable source. Latently-infested nursery stock is the major source of crown gall disease in vineyards.
• Hot water treatment of vines is effective in reducing crown gall infection levels in planting materials. 

After Planting

There is little that can be done to control this disease once it is established in the vineyard other than to avoid injury to vines (winter, mechanical and human) that will activate the disease.

• Remove suckers when shoots are small (3 to 6 cm) to reduce trunk damage and promote rapid healing of wounds. Removing larger shoots before they harden will result in clean and small scars.
• Hill young vines with 30 cm or more of soil or other material in the fall to protect graft unions and the lower trunk from cold injury.  This will ensure new shoots for trunk renewal or replacement the following season. Remove this soil carefully in the spring to avoid mechanical damage.
• Avoid injuring vines during cultivation since the soil-inhabiting pathogen enters through wounds, particularly in spring and early summer.
• Do not overcrop.
• Use multiple trunks.  If one trunk develops crown gall and has to be removed, the vine will continue to bear fruit on the symptomless trunk and a renewal cane can be trained from above the graft union.
• Remove galled and girdled trunks and train new trunks. Partially galled trunks may outgrow the gall, but success is determined by the susceptibility of the cultivar and the environmental conditions that trigger gall development.
• When replacing vines killed by crown gall, remove the dead vine and as much of the root mass as possible since the pathogen can live for years on decaying roots.
• Topical chemical treatments are ineffective as the pathogen is systemic in the grapevine and new galls will develop around or beyond the treatment site. Soil fumigation is generally ineffective particularly in heavier soils, but also in light textured soils where roots often extend deeper than the fumigant application. The pathogen can remain viable in the soil as long as infected living root material is present.
• Limit applications of nitrogen in the late fall or early spring. Vines that do not adequately harden off have a higher water content going into the winter and are more prone to winter injury and crown gall infection. Vines growing in wet sites that grow vigourously late in the season will typically be more prone to injury and crown gall infection.  Similarly, rapid growth in the spring can cause bark splitting which can act as entry points for infection.
• Wind machines mix warm air from above the vineyard with cold air closer to the ground, reducing cold injury.