How to Manage Pests

UC Pest Management Guidelines

Cherry

Bacterial Canker

Pathogen: Pseudomonas syringae

(Reviewed 11/09, updated 11/09)

In this Guideline:

Symptoms and Signs

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.

Comments on the Disease

Pseudomonas syringae survives 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 rarely occurs in first year of planting, and is uncommon in nurseries.

Management

The occurrence of bacterial canker is thought to be related to the amount of stress trees are subjected to, including poor nitrogen and/or microelement availability, high ring-nematode populations, previous drought stresses, hardpan, rootstocks that reduce tree vigor, spring freezes, and irrigation methods that wet the tree. If ring-nematode populations are present in an orchard site, preplant fumigation is important. Also important are rootstock selection, proper nitrogen fertilization, and the use of drip or microsprinkler irrigation, which may help with nutrient uptake. Of the rootstocks commonly used for cherries in California, Mahaleb is the most tolerant of bacterial canker, Colt is moderately susceptible, and Mazzard is susceptible. Spring and summer pruning may also help. Fall and dormant season copper sprays have been used by some growers to help manage this disease, but research in California orchards has not shown this practice to be consistent or reliably effective. There is also widespread copper resistance in pathogen populations in commercial orchards.

Treatment Decisions

In light, sandy soils and in some heavy soils, control has been achieved with preplant fumigation for nematodes. Ring nematodes predispose cherry trees to bacterial canker. The benefits of preplant soil fumigation for control of bacterial canker usually last only a few years; in some areas only limited improvements in disease control occur following soil fumigation.

Common name		Amount per acre	R.E.I.‡	P.H.I.‡
(trade name)			(hours)	(days)
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees (PDF), and environmental impact. Not all registered pesticides are listed. Always read the label of the product being listed.
PREPLANT
A.	METHYL BROMIDE*	300-600 lb	See label	NA
	COMMENTS: Use allowed under List of Approved Critical Uses. Use higher rates for fine-textured soils. Fumigants such as methyl bromide are a source of volatile organic compounds (VOCs) but are not reactive with other air contaminants that form ozone; methyl bromide depletes ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
‡	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
*	Permit required from county agricultural commissioner for purchase or use.
NA	Not applicable.

PUBLICATION

UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440

Diseases

• J. E. Adaskaveg, Plant Pathology, UC Riverside
• J. L. Caprile, UC Cooperative Extension, Contra Costa County

Acknowledgment for contributions to Diseases:

• W. D. Gubler, Plant Pathology, UC Davis
• B. L. Teviotdale, Kearney Agricultural Center, Parlier

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