Bacterial Canker
Beginner
This pest affects:
 |
 |
 |
Scientific Name
Pseudomonas syringae pv.syringae (morsprunorum)
Identification
Trunks, limbs, and branches
- On young trees, elongated cankers that are soft and spongy with copious gumming
- Cambium at the canker will be discoloured and necrotic
- Cankers may expand rapidly in spring causing girdling of main trunk or branches
- Cankers on trunks, limbs and branches exude gum during late spring and summer
- Leaves on the terminal portions of cankered limbs and branches may wilt and die in summer or early autumn if girdled by a canker
- Occasionally, large scaffold limbs are killed
- Older trees have a bare-branch or leggy appearance caused by extensive killing of leaf and flower buds and spurs on wood 3 years of age or older
- Cankers or dark sunken areas around dead buds and spurs and in the crotch angles
Leaves
- Sporadic occurrence
- Initially water-soaked lesions, becoming dry, dark brown, circular to angular sometimes surrounded with yellow halos
- Centres of lesions fall out giving shot-hole appearance
- The spots may coalesce to form large patches of dead tissue, especially at margins of leaves, resulting in tattered leaves
- Infected leaves may fall off midseason
Fruit
- Sporadic occurrence
- Lesions initially brown with a margin of wet or water-soaked tissue on green fruit
- Becoming deep, black depressions in the flesh, with margins becoming yellow to red as lesions and fruit age
- Elliptical brown lesions with water-soaked margins on fruit stems
Blossoms & Buds
- Infected leaf and flower buds may fail to open in spring
- Small cankers often develop at the bases of these buds
- Other infected buds open in spring but collapse in early summer, leaving wilted leaves and dried-up fruit
- If blossom infection occurs, whole blossom clusters collapse (blossom blast) as infection spreads into the fruit-bearing spurs (spur blast)
Often Confused With
Frost damage to buds – no cankers at base of bud; no foliar spotting or shothole
Perennial canker – no foliar spotting or shothole; elliptical sunken cankers along the length of the trunk or limb surrounded by a series of callus rings
Period of Activity
Outbreaks of bacterial canker are often associated with prolonged periods of cold, wet weather with late spring frosts.
Scouting Notes
Cankers develop in winter and early spring.
Use a pocket knife cut below canker to look for discoloured cambium tissue.
Threshold
No threshold established.
Advanced
This pest affects:
|
|
|
Scientific Name
Pseudomonas syringae pv.syringae (morsprunorum)
Identification
Trunks, limbs, and branches
- On young trees, elongated cankers that are soft and spongy with copious gumming
- Cambium at the canker will be discoloured and necrotic
- Cankers may expand rapidly in spring causing girdling of main trunk or branches
- Cankers on trunks, limbs and branches exude gum during late spring and summer
- Leaves on the terminal portions of cankered limbs and branches may wilt and die in summer or early autumn if girdled by a canker
- Occasionally, large scaffold limbs are killed
- Older trees have a bare-branch or leggy appearance caused by extensive killing of leaf and flower buds and spurs on wood 3 years of age or older
- Cankers or dark sunken areas around dead buds and spurs and in the crotch angles
Leaves
- Sporadic occurrence
- Initially water-soaked lesions, becoming dry, dark brown, circular to angular sometimes surrounded with yellow halos
- Centres of lesions fall out giving shot-hole appearance
- The spots may coalesce to form large patches of dead tissue, especially at margins of leaves, resulting in tattered leaves
- Infected leaves may fall off midseason
Fruit
- Sporadic occurrence
- Lesions initially brown with a margin of wet or water-soaked tissue on green fruit
- Becoming deep, black depressions in the flesh, with margins becoming yellow to red as lesions and fruit age
- Elliptical brown lesions with water-soaked margins on fruit stems
Blossoms & Buds
- Infected leaf and flower buds may fail to open in spring
- Small cankers often develop at the bases of these buds
- Other infected buds open in spring but collapse in early summer, leaving wilted leaves and dried-up fruit
- If blossom infection occurs, whole blossom clusters collapse (blossom blast) as infection spreads into the fruit-bearing spurs (spur blast)
Often Confused With
Frost damage to buds – no cankers at base of bud; no foliar spotting or shothole
Perennial canker – no foliar spotting or shothole; elliptical sunken cankers along the length of the trunk or limb surrounded by a series of callus rings
Biology
Bacterial canker is mainly a problem on sweet cherry although it can also occur on sour cherry and plum. Young cherry trees are more susceptible than established cherry trees, and trees under stress are much more susceptible than healthy trees with optimal growing conditions. Heading cuts of first year whips are especially susceptible and can be infected up to 3 weeks after pruning during the winter. Tree mortality is generally greatest in the first 2 years after planting and trees are seldom killed after 8 years.
The bacteria survive the winter in bark around small cankers, in infested buds, and the vascular system of infected trees. Under cool, wet conditions in the spring, the bacteria infect buds and leaf scars and tissue damaged by frost, pruning cuts or insects. Splashing rain disperses the pathogen to susceptible tissue. Infection has been demonstrated at temperatures as low as 6°C.
Small cankers eventually form at the base of the dead buds and often exude gum during the late spring or early summer. Bacteria can also survive on the surfaces of leaves and blossoms without causing any damage throughout the growing season. Leaf and fruit infections can be of economic significance in years with prolonged wet cold weather during or shortly after bloom. Blossom blast and spur blast are most likely in years when leaf and fruit infections are common.
As the tree begins growth in spring, the bacteria population declines and a callus layer forms around the canker’s edge. During spring and summer, girdled and nearly girdled limbs may leaf out. Normally, leaves turn yellow, then the limbs usually die. In some instances, these symptoms may not appear until late summer when the leaves’ water requirement is high.
During the warmer and dryer summer months, the bacteria populations tend to be low. In the autumn particularly when conditions are wet and cool, the bacteria multiply and may enter the host trees through the leaf scar up to two or three days after leaf fall.
Period of Activity
Outbreaks of bacterial canker are often associated with prolonged periods of cold, wet weather with late spring frosts.
Scouting Notes
Cankers develop in winter and early spring.
Use a pocket knife cut below canker to look for discoloured cambium tissue.
Threshold
No threshold established.
Management Notes
Bing, Lambert, Sweetheart, Schmidt, Hedelfingen and Van are very susceptible to bacterial canker. Viva, Venus, Vic, Vega, and Victor are considered moderately resistant. Mazzard F12-1 is one of the most resistant rootstocks. Resistance of new rootstocks is unknown at this time, but trees on Mazzard may have an advantage over trees on size controlling rootstocks.
Avoid planting sweet cherry orchards beside sour cherry orchards. Sour Cherry trees may harbour the pathogenic bacteria populations, which spread to the sweet cherry orchards resulting in economic losses.
Ideally locate orchard in a frost free area. If planting in the spring, plant orchards after frost is likely to occur.
Before establishing new orchards, have soil tested for pathogenic nematodes. High nematode populations, particularly the 'ring nematode' are associated with increased losses due to bacterial canker. Fumigate soil before planting if nematode populations are high.
Use scions or buds from virus-free, canker-free trees. Make buds or grafts at least 12 to 15 inches away from the trunk.
Make heading cuts after planting only during dry weather when rain will not occur for at least a week after pruning.
Do not interplant new trees with infected old trees which are a major source of the bacteria.
Keep trees healthy and prevent stresses that may predispose them to infection including maintaining a balanced nutrient program, keeping soil pH around 6.0 – 6.5 and managing other disease and insects.
Paint all trunks white with latex paint to prevent winter injury.
Prune when trees are fully dormant or, if pruning must be done in the spring, wait for a few days of forecasted warm, dry weather so pruning cuts can heal more rapidly. Remove severely affected trees, and prune off dead or dying branches. Avoid pruning in early spring and fall when bacteria are most active. Sterilizing pruning tools between cuts is not beneficial for reducing transmission of bacterial canker.
Prune out branches with cankers.
In summer, small cankers may be cut out using the following method. Cut away bark above and around the edges of the infected area. Use sharp tools, and leave wound margins smooth and neat. In non-irrigated orchards, wounds may be left uncovered during summer but should be treated with a wound dressing before fall rains begin. In sprinkler-irrigated orchards wounds may be soaked frequently, so they should be covered with a dressing as soon as possible after cutting.
Control weeds in the tree row. Pseudomonas cells are present everywhere; however, the type of cover crop in an orchard does affect the population of the pathogen. Pseudomonas is more prevalent on grasses and dandelions than on clover.
Keep irrigation water off the part of the trees above ground as much as possible for the first 2 or 3 years after planting. Consider withholding water in late summer so trees will "harden off" and not be as susceptible to low temperature injury in early winter.
Registered copper products suggest two applications per year; one in the fall when 75% of leaves have dropped and one in the spring before bud break. Spring applications are risky if buds are too far along since copper is quite phytotoxic to sweet cherry. Fall applications probably reduce surface populations of P. syringae, but at 75% leaf drop, there has been plenty of opportunity for the bacteria to invade and be protected in small leaf scars. Copper sprays do not eliminate the disease and at best, can only help suppress P. syringae that have not already infected plant tissues.
Some information included above excerpted from;
