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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Rust lesions on upper leaf surface.

Prune

Rust

Pathogen: Tranzschelia discolor

(Reviewed 6/06, updated 6/06)

In this Guideline:

SYMPTOMS

The most common symptoms of rust are bright yellow, angular spots on leaves, with red-brown spore masses on lower sides of leaf, and premature defoliation.

COMMENTS ON THE DISEASE

The rust pathogen depends on moisture for infection. Twig lesions do not occur on prune trees.

MANAGEMENT

If rust is a problem in an orchard, evaluate the orchard to develop a treatment program. Treating at bloom won't be effective because it is too far in advance of leaf symptoms.

Begin monitoring orchards by May 1; in the San Joaquin Valley monitor at least every other week and in the Sacramento Valley monitor every week until July 15. Examine 40 trees randomly each time. Examine each tree for the presence of leaves with prune rust symptoms; be sure to look at low hanging branches. In addition, be sure to monitor nonbearing replants in the orchard, trees with vigorous growth, and known rust hot spots. If there are no trees with rust present, continue to monitor weekly or every other week.

Treat at the first sign of rust in the orchard. Additional treatments may be necessary, especially if a treatment was required early in the season. After a treatment is applied, continue to monitor weekly or twice monthly. If the number of trees with rust increases from the last reading, a second treatment is recommended if there is significant time remaining to harvest. No additional treatments or monitoring are necessary within 4 weeks of harvest.

Common name Amount to Use
(trade name)  
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy. When choosing a pesticide, also consider information relating to environmental impact.
 
A. AZOXYSTROBIN
  (Abound) 12.3–15.4 fl oz
  MODE OF ACTION: A Qol (Group 11)1 fungicide.
  COMMENTS: A strobilurin fungicide. Do not apply more than three sequential applications for rust control before alternating with a fungicide that has a different mode of action.
 
Note: Minimize the use of sulfur because it kills predatory mites, leading to an increase in mite populations.
B. WETTABLE SULFUR# 20 lb
  MODE OF ACTION: A multi-site contact (Group M2)1 inorganic fungicide.
  COMMENTS: Controls rust for only 2 weeks.
 
C. SULFUR DUST# 50 lb
  MODE OF ACTION: A multi-site contact (Group M2)1 inorganic fungicide.
  COMMENTS: Controls rust for only 2 weeks.
 
 
#  Acceptable for use on organically grown produce.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different Group number are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.

More information on prune fungicides

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
C. Pickel, UC IPM Program, Sutter/Yuba counties
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
W. H. Olson, UC Cooperative Extension, Butte County
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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