Symptoms and Signs
Symptoms are most obvious in spring, and include limb dieback with rough cankers and amber-colored gum 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 numbers 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 the 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, rip or backhoe to break up hardpan areas. When replanting an orchard, fumigate the soil before planting to reduce ring nematode numbers. Consider using Viking, Lovell, or Guardian rootstocks, as they survive significantly better in the presence of this disease.
- Trees planted on Marianna 2624 and peach-almond hybrid (Hansen, Nickels, Cornerstone, Titan, and Bright's) rootstocks are very susceptible to bacterial canker.
- 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. Most strains of the pathogen are resistant to copper.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| PREPLANT | ||||
| A. | 1,3-DICHLOROPROPENE* | |||
| (Telone II) | Label rates | See label | See label | |
| COMMENTS: This restricted-use fumigant is applied only by professional fumigation companies. 1,3-dichloropropene is a multipurpose liquid fumigant for preplant treatment of soil to help manage certain soil borne diseases and to control other pests (e.g., plant parasitic nematodes and symphylans) in croplands. 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. Do not apply this product in a way that will contact workers or other persons, either directly or through drift. Only handlers may be in the application block from the start of the application until the entry restricted period ends, and in the buffer zone during the buffer zone period. 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. | ||||
| B. | 1,3-DICHLOROPROPENE*/CHLOROPICRIN | |||
| (Telone C-35) | Label rates | See label | See label | |
| COMMENTS: This restricted-use fumigant is applied only by professional fumigation companies and is a multipurpose liquid fumigant for preplant treatment of soil to help manage certain soil-borne diseases and to control other pests (e.g., plant parasitic nematodes and symphylans) in croplands. It is effective at 39 to 46.7 gal/acre rate (shank 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. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 action. 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 a fungicide with a different mode-of-action group number. |