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How to Manage Pests
UC Pest Management Guidelines
Almond
Rust
Pathogen: Tranzchelia
discolor
(Reviewed 3/09,
updated 3/09)
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 more likely to become serious in orchards near rivers or
streams or other locations where humidity is relatively high in spring and
summer. Excessive levels of nitrogen are also known to increase the tree's
susceptibility. The disease causes leaves to fall prematurely and will weaken
trees, reducing the following year's bloom if not controlled. Rust is often
observed in second- and third-leaf nonbearing orchards where fungicides have
not been applied.
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 sulfur or maneb 5 weeks
after petal fall and follow 4 to 5 weeks later in late spring and summer with a
QoI fungicide (FRAC Group number 11) 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.
When zinc sulfate (20-40 lb/acre) is applied in late October to
early November to hasten leaf fall, rust inoculum is prevented from increasing.
Otherwise, the inoculum may build up, overwinter on the trees, and infect
leaves the following spring.
| 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 fungicide resistance and environmental impact. |
| |
| A. |
PROPICONAZOLE |
| |
(Orbit) |
8 fl oz |
12 |
60 |
| |
MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) |
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| B. |
PYRACLOSTROBIN /BOSCALID |
| |
(Pristine) |
10.5–14.5 oz |
12 |
25 |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7) |
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COMMENTS: Chemical class: carboxyanilide/strobilurin.
See label for current preharvest interval. Do not make more than 4
applications per season of strobilurins or carboxyanilides to limit the potential for the development of resistance. |
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| C. |
AZOXYSTROBIN |
| |
(Abound) |
12.3–15.4 oz |
4 |
28 |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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COMMENTS: 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 2.88 qt/product/acre/season. |
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| D. |
TRIFLOXYSTROBIN |
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(Gem) |
3–4 oz |
12 |
60 – see comments |
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MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) |
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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 |
24 |
145 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3) |
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COMMENTS: Do not apply more than 32 lb of product/acre/season. |
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| F. |
WETTABLE SULFUR# |
Label rates |
24 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
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COMMENTS: 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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| G. |
SULFUR DUST# |
50 lb/acre |
24 |
0 |
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MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2) |
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COMMENTS: 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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UC IPM Pest Management Guidelines: Almond
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
B. A. Holtz, UC Cooperative Extension, Madera County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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