How to Manage Pests
UC Pest Management Guidelines
Pathogen: Pseudomonas syringae
In this Guideline:
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.
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.
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.
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
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
||Amount to Use
choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are listed. Always
read label of product being used.
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.
||33.7 gal/broadcast acre
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.
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.
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.
UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
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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