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How to Manage Pests
UC Pest Management Guidelines
Apricot
Bacterial
Canker
Pathogen: Pseudomonas
syringae
(Reviewed 11/07,
updated 11/07)
In this Guideline:
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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.
Orange or red flecks and
pockets of bacterial invasion under the bark occur outside canker margins.
Frequently, trees sucker from near ground level; cankers do not extend below ground.
Pseudomonas syringae survives on plant surfaces, is spread by splashing rain, and is
favored by high moisture and low temperatures in spring. The bacterium is
commonly found on healthy as well as diseased plants and becomes pathogenic
only on susceptible or predisposed trees.
The disease is found almost exclusively in
replanted orchards where ring nematodes flourish or in locations where spring
frost is a problem. The disease is worse in low, gravelly, 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
the first year of planting unless the ground is not fumigated before planting
and is uncommon in nurseries.
The key to bacterial canker management is control of ring nematodes
and maintaining healthy, vigorous trees. Any management practice that improves
tree vigor (e.g., lighter, more frequent irrigation with drip or
microsprinklers, improved tree nutrition [especially nitrogen], etc.) will help
reduce the incidence of this disease.
It is very important to fumigate sandy soils
when apricot trees are to be planted following an old apricot, peach, almond,
or other Prunus spp.
orchard. Rootstocks of plum parentage (e.g. Myrobalan, Marianna 2624) are
highly susceptible to bacterial canker. Lovell peach and Viking rootstocks are
more tolerant than Nemaguard or apricot rootstocks. In soils with high levels
of ring nematodes, annual fall treatments with a nematicide are beneficial.
There is evidence that pruning during the dormant period may make trees more
susceptible than pruning after trees become active in spring or pruning in
summer. Copper sprays applied at the beginning and end of leaf fall have been
tried with highly variable results.
Management Decisions
In light,
sandy soils and in some heavy soils, control has been achieved with preplant
fumigation for ring nematodes. Nematodes stress trees, which predisposes them
to bacterial canker. The benefits of preplant soil fumigation for control of
bacterial canker usually last only a few years.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(days) |
|
| When choosing a pesticide, consider the general
properties of the fungicide as well as information relating to environmental impact.
|
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| PREPLANT |
| A. |
1,3-DICHLOROPROPENE*/CHLOROPICRIN* |
| |
(Telone C35) |
see comments |
7 days |
0 |
| |
COMMENTS: Chloropicrin tends to invigorate young trees, which
can be advantageous in replant situations and where one Prunus orchard replaces a previous one. This restricted
use product is applied only by professional fumigation companies. It is
effective at 33.7 gal/acre rate 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
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. |
| |
| B. |
1,3-DICHLOROPROPENE* |
| |
(Telone II) |
33.7 gal/broadcast acre |
7 days |
0 |
| |
COMMENTS: This restricted use product is applied only by
professional fumigation companies. It is effective at 33.7 gal/acre rate 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
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. |
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UC IPM Pest Management Guidelines: Apricot
UC ANR Publication 3433
Diseases
J. E. Adaskaveg, Plant Pathology, UC Riverside
W. D. Gubler, Plant Pathology, UC Davis
W. W. Coates, UC Cooperative Extension, San Benito Co.
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
J. L. Caprile, UC Cooperative Extension, Contra Costa Co.
B. A. Holtz, UC Cooperative Extension, Madera Co.
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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