How to Manage Pests
UC Pest Management Guidelines
Pathogen: Pseudomonas syringae
(Reviewed 6/10, updated 6/10, pesticides updated 9/15)
In this Guideline:
Symptoms are most obvious in spring and include limb dieback with rough cankers and amber-colored gum. There may also be leaf spot and blast of young flowers and shoots. The sour sap phase of bacterial canker may not show gum and cankers, but the inner bark is brown, fermented, and sour smelling. Flecks and pockets of bacterial invasion in bark occur outside canker margins. Frequently, trees sucker from near ground level; cankers do not extend below ground.
Pseudomonas syringae is a ubiquitous bacterium that survives in or on plant surfaces, is spread by splashing rain, and is favored by high moisture and low temperatures in spring. The disease is worse in low or sandy spots in the orchard. Vigorous trees are less susceptible to bacterial canker, while young trees, 2 to 8 years old, are most affected. The disease complex rarely occurs in the first year of planting and is highly uncommon in nurseries. It is a frequent problem in replant situations; however, the severity of bacterial canker in an orchard is highly correlated with the presence of ring nematode in the soil.
The key to managing bacterial canker is keeping the trees as tolerant as possible to the disease rather than trying to kill the bacterial pathogen. Problems with bacterial canker can be minimized at planting by carefully selecting the planting site, choosing the least susceptible rootstocks, and following recommended cultural practices regarding pruning and fertilizing. Bacterial canker tends to mostly affect weak trees, so any management practice that improves tree vigor (e.g., lighter, more frequent irrigation, improved tree nutrition, nematode management, etc.) will help to reduce the incidence of this disease. Delayed pruning may help. Lovell peach and Viking rootstocks are usually more tolerant than Nemaguard.
In light, sandy soils and in some heavy soils, control has been achieved with preplant fumigation for ring nematodes. Applications of copper are not effective against bacterial canker.
Organically Acceptable Methods
Cultural controls are acceptable for use in an organically certified crop.
Following planting, if bacterial canker occurs in an orchard, apply nematicide around all trees in the affected area of the orchard on a yearly basis until the trees are 8 years old.
UC IPM Pest Management Guidelines: Nectarine
J. E. Adaskaveg, Plant Pathology, UC Riverside
Acknowledgment for contributions to Diseases:B. L. Teviotdale, Kearney Agricultural Center, Parlier
W. D. Gubler, Plant Pathology, UC Davis