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 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. 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,
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.
In light, sandy soils and in some heavy soils,
control has been achieved with preplant fumigation for ring nematodes. Applications of copper are not effective
against bacterial canker.
Organically Acceptable Methods
controls are acceptable for use in an organically certified crop.
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, and in some
areas only limited improvements in disease control occur following soil
planting, if bacterial canker occurs in an orchard, apply nematicide around all
trees in the affected area of the orchard on a yearly basis until the trees are
8 years old.
||Amount to Use
|When choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are
listed. Always read label of product being used.
||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.
||33.7 gal/broadcast acre
||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.
UC IPM Pest Management Guidelines: Nectarine
UC ANR Publication 3451
J. E. Adaskaveg, Plant Pathology, UC Riverside
R. A. Duncan, UC Cooperative Extension Stanislaus County
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
W. D. Gubler, Plant Pathology, UC Davis
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