Cankers in nursery stock species are characterised by the death of cambium (inner bark) tissue of woody stems, branches or twigs, causing them to sink in. They can completely girdle the stem, disrupting the vascular system so that shoots beyond the canker wilt and die through a lack of water.
Large numbers of smaller cankers can also disrupt vascular systems enough to cause gradual wilting and shoot death.
The most common canker pathogens are the fungus Nectria galligena, which causes cankers on subjects such as apple, pear, willow, mountain ash, beech and poplar, and the bacterium Pseudomonas syringae, which exists as a large number of subspecies and can cause cankers in a wide range of trees and shrubs.
Pseudomonas syringae pv. mors-prunorum is widespread and serious on cherry and plum but also found on almond, apricot, peach and related ornamentals. Other Pseudomonas species can attack berberis and philadelphus.
A low pH in growing media can create a papery bark-like canker (high manganese availability), especially on container-grown trees.
Notifiable diseases (producing canker-like symptoms)
Including Xanthomonas campestris pv. Pruni on Prunus spp. and fireblight (Erwinia amylovora), which causes cankers at late infection stages.
How to distinguish them
Fungal cankers White, orange or pink conidial (spore-producing) pustules develop on infected tissue in summer, followed by small red perithecae, which produce ascospores. In early stages, lesions may produce blobs of amber gum.
Bacterial cankers Xanthomonas populi or forms of Pseudomonas syringae. Creamy slime or sticky gum oozes from canker lesions, particularly in spring. Xanthomonas populi may cause orange staining of outer wood at infection sites.
Xanthomonas campestris pv. pruni Leaf spots may exude bacterial slime.
Erwinia spp. Foliage looks burnt and girdled stems form a "shepherd’s crook" shape. Affected plant material and blossom can exude bacterial ooze and usually remain attached to the plant.
Canker lesions themselves, including those caused by physical or physiological injury, can provide entry points for other pathogens or wood decay fungi, which may lead to symptoms that mask the true identity of the primary infection.
In Pseudomonas bacterial canker of prunus, Pseudomonas syringae may infect leaves in summer. Cankers are initiated in autumn by bacteria splashed from the leaves that enter stems through abscission scars.
The bacteria lie dormant over winter and lesions develop in spring.
The characteristic depressed lesion of canker infections is caused by the arrested development of the infected bark tissue. Corky tissue layers may even be actively produced by the plant around the lesion as a means of defence.
These may impede the canker’s progress but will not prevent the infection from spreading.
Other bacterial cankers include:
ash canker (Pseudomonas syringae spp. savastanoi pv. fraxini) and poplar canker (Xanthomoas populi). Pseudomonas and Xanthomonas can only be distinguished with certainty by lab analysis.
Significant fungal cankers include:
Nectria galligena on apples and pears; robinia canker (Nectria haematococca var. brevicona); black canker (Glomerella miyabeana), which attacks Salix alba, among others; stem blight (Diaporthe kalmiae); Coryneum canker (Seiridium cardinale), which can attack Chamaecyparis, Cupressus and × Cupressocyparis leylandii (resistant trees include Thuja occidentalis and Juniperus virginiana); Phomopsis canker (Phomopsis juniperovora), particularly on Juniperus sabina ‘Tamariscifolia’; Amylostereum canker (Amylostereum laevigatum) on Taxus and junipers; and finally Phytophthora bleeding canker (Phytophthora cactorum and P. citricola) on Aesculus and Tilia.
Treatment: cultural control
Avoid unnecessary wounding, improve air circulation around plants, remove and destroy fallen leaves and make sure that tree ties do not become too tight. Wash pruning tools in disinfectant between cuts
and avoid pruning plants in wet conditions. Make sure that all equipment used is kept sharp.
In deciduous tree production, consider the use of chemical defoliants during autumn to help ensure well-healed abscission scars.
Treatment: biological control
Use Prestop* (Gliocladium catenulatum strain J1446), Revive P, Serenade ASO* (Bacillus subtilis
strain QST713) or Trianum P (Trichoderma harzianum) as part of
a prevention strategy.
Treatment: chemical control
A copper-based fungicide will help prevent bacteria from infecting stems and foliage. Apply to small areas of crop first to check for phytotoxicity.
Fungal canker controls
Active ingredient Tebuconazole
FRAC code 3
Formulation Various including Folicur (Bayer)
Action(s) Systemic fungicide for outdoor crops. Compatible with biological controls.
Bacterial canker controls
Active ingredient Bacillus subtilis
Formulation Serenade ASO* (Various)
Action(s) Protectant bio-fungicide compatible with biological controls.
Active ingredient Copper oxychloride
FRAC code M1
Formulations Cuprokylt* (Certis)
Action(s) Protectant fungicide. Compatible with some biological controls. Check the CRD website for latest emergency approval/EAMU information. ν
Fully updated by Dove Associates
Use plant protection products safely. Always read the label and product information before use.
* EAMU required for use in ornamental plant production outdoors and/or under protection.
Dove Associates shall in no event be liable for the loss of or damage to any crops or biological control agents caused by the use of products mentioned.