How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms are most obvious in spring and include limb dieback with 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 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, and the severity of bacterial canker in an orchard is highly correlated with the presence of ring nematode in the soil.

MANAGEMENT

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. An application of copper during dormancy is not effective against bacterial canker.

Organically Acceptable Methods
Cultural controls are acceptable for use in an organically certified crop.

Chemical Control
Bactericide applications have no reliable effect on bacterial canker and their use is not recommended. Preplant fumigation for nematode control reduces the severity of bacterial canker in newly planted orchards. Ring nematodes stress trees, which predispose them 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.

Following planting, if bacterial canker occurs in an orchard, apply nematicide around all trees in the affected area of the orchard on an annual basis until the trees are 8 years old.

Common name		Amount to Use	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
PREPLANT
A.	METHYL BROMIDE*	300–600 lb	see label	see label
	COMMENTS: Must be applied under a Critical Use Exemption. 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.
B.	1,3-DICHLOROPROPENE*
	(Telone II)	33.7 gal/broadcast acre	5 days	NA
	COMMENTS: This restricted use product is applied only by professional fumigation companies. It is effective at 33.7 gal/acre rate (top label rate for broadcast applications) if applied to dried sandy soils or sandy loam soils with no more than 12% soil moisture content anywhere in the surface 5 feet of soil profile. In California the applications must be applied to soils having a moist surface; this task is difficult to achieve without use of sprinklers unless there is a fortunate rainfall. Do not flood irrigate prepared lands to achieve this surface moisture requirement. Broadcast apply where nematode resistance is unavailable for prevailing nematodes. Strip applications are permitted at higher treatment rates and effective where resistant rootstocks are available, the clay loam soil profile contains no more than 19% soil moisture, the field has been pre-ripped to 4- or 5-foot depth, and the delivery shank is winged to limit off-gassing. Fumigants such as 1,3-dichloropropene are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
POSTPLANT
A.	SODIUM TETRATHIOCARBONATE*
	(Enzone)	750–1,000 ppm	4 days	0
	COMMENTS: Liberates carbon bisulfide soon after soil contact and its half-life may not exceed 24 hours. Thus, performance is limited to soils that quickly infiltrate 2 to 3 inches of water within several hours. Enzone is quite effective against nematodes external to the roots, particularly ring and dagger nematodes in coarse textured soils applied via low volume during a 4-hour irrigation. Apply during cooler months before May 1 or after October 15 and no more than twice per year. Fall applications can halt bacterial canker incidence the following spring.
+	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: Peach
UC ANR Publication 3454
Diseases
J. E. Adaskaveg, Plant Pathology, UC Riverside
R. A. Duncan, UC Cooperative Extension Stanislaus County
J. K. Hasey, UC Cooperative Extension Sutter/Yuba counties
K. R. Day, UC Cooperative Extension Tulare County
Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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