How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms are most obvious in spring and include limb dieback with rough cankers and amber colored gum and/or total tree collapse. There may also be leaf spots and blast of young flowers, spurs, 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 occurs almost exclusively in orchards where almond or other Prunus spp. orchards previously existed. The disease is worse in low (cold) or sandy spots with high populations of ring nematode. Nitrogen deficient trees are most prone to bacterial canker as are young trees that are 2 to 8 years old. The disease rarely occurs in first year of planting and is uncommon in nurseries.

MANAGEMENT

The pathogen that causes bacterial canker is commonly present on the surfaces of many plants. Consequently, management of this disease should focus on preventing conditions that predispose trees to the disease.

• Before planting, properly sub-soil the orchard to break up hard-pan areas. When replanting an orchard, fumigate the soil before planting to reduce ring nematode populations. Consider using the Viking rootstock as one that has shown better survival in the presence of this disease.
• Trees planted on Marianna 2624 and peach-almond hybrid (Hansen, Nickels, and Bright's) rootstocks are very susceptible to bacterial canker. Of the rootstocks that are somewhat resistant to the disease, Lovell rootstock produces trees that are more tolerant than those growing on Nemaguard.
• Maintaining proper nutrition, particularly nitrogen, is important.
• Recent studies have shown that when low biuret urea is applied before leaf drop, canker size in infected trees is reduced.
• Annual nematicide treatments in October can help reduce disease severity.

Dormant use of copper has not been found to provide successful suppression of this disease in California.

Common name		Amount/Acre	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.	1,3-DICHLOROPROPENE*
	(Telone II)	Label rates	5 days	0
	COMMENTS: 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)	750–1200 ppm	4 days	0
	MODE OF ACTION GROUP NAME (NUMBER1): Unknown. A thiocarbonate fungicide.
	COMMENTS: Most effective when applied in drip irrigation.
+	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.
1	Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
Roger Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center
B. A. Holtz, UC Cooperative Extension, Madera County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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