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How to Manage Pests
UC Pest Management Guidelines
Almond
Rust
Pathogen: Tranzchelia
discolor
(Reviewed 1/05,
updated 1/05)
In this Guideline:
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Rust appears as small, yellow spots on the upper surface of leaves. On the
lower surface of the leaf these spots take on a rusty red appearance when the
rust-colored spores produced in the lesions erupt through the surface. These
spores are spread by air movement and infect other leaves to continue the
disease cycle. Young twigs may be infected, but twig lesions are seldom seen on
almond.
Rust occurs sporadically throughout almond-growing areas in California. It is
most likely to become serious in orchards near rivers or streams or other
locations where humidity is relatively high in spring and summer. The disease
causes leaves to fall prematurely and will weaken trees if not controlled.
The development of rust is favored by humid conditions, and the disease becomes
worse when rain occurs in late spring and summer. Trees can be defoliated
quickly when rust becomes severe. The rust fungus survives from one season to
the next in infected leaves and possibly also in infected twigs.
In orchards with a history of rust, apply fungicide in late spring and summer
to control leaf infections. Two or three applications may be needed in orchards
that have had severe rust problems. To be effective, fungicide must be applied
before rust symptoms are visible.
To prevent the rust inoculum from increasing in late fall, apply zinc sulfate
(20-40 lb/acre) in late October to early November to hasten leaf fall.
Otherwise, the inoculum may build up, overwinter on the trees, and infect
leaves the following spring.
| Common name |
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P.H.I.+ |
| (trade name) |
Amount/Acre |
(days) |
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| Fungicides are listed in general order of efficacy. |
| A. |
WETTABLE SULFUR# |
Label rates |
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COMMENTS: Chemical class: inorganic. To be effective,
sulfur treatments must be applied before rust symptoms appear, which can be
anytime from late spring through fall. Do not apply within 3 weeks of an oil
application. |
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| B. |
SULFUR DUST# |
50 lb/acre |
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COMMENTS: Chemical class: inorganic. To be effective,
sulfur treatments must be applied before rust symptoms appear, which can be
anytime from late spring through fall. Do not apply within 3 weeks of an oil
application. |
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| C. |
AZOXYSTROBIN |
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(Abound) |
12.3-15.4 oz |
28 |
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COMMENTS: Chemical class: strobilurin fungicide. Do
not apply more than 3 sequential sprays before alternating with a fungicide
that has a different mode of action. Do not apply more than 4 applications of
strobilurin fungicides/year or apply more than 1.92
qt/product/acre/season. |
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| D. |
TRIFLOXYSTROBIN |
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(Flint) |
3-4 oz |
60 — see comments |
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COMMENTS: Chemical class: strobilurin. Do not apply
within 60 days of harvest or after hull split. Do not exceed more than 3
applications of all strobilurins per season to limit the potential for the
development of resistance. Do not apply more than 12 oz/acre/season. |
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| E. |
MANEB |
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(various) |
Label rates |
145 |
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COMMENTS: Chemical class: carbamate (ethylene
bisdithiocarbamate). Do not apply more than 32 lb of product/acre/season. |
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More information on almond fungicides
UC IPM Pest Management Guidelines: Almonds
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
Acknowledgment for contributions to the disease section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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