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UC Pest Management Guidelines


Rust symptoms on fruit and leaves.

Peach

Rust

Pathogen: Transchelia discolor

(Reviewed 4/10, updated 4/10)

In this Guideline:


SYMPTOMS AND SIGNS

Infections of young twigs and leaves are the most common symptoms of rust, but in California, fruit infections may be a major component of the disease as well.

Twig Cankers
Twig cankers are the first symptoms of the disease in spring. Cankers develop after petal fall on 1-year-old fruiting wood. They appear as blisters and longitudinal splits in the bark about 0.12 to 0.25 inches long. They can most easily be seen using a 20X hand lens.

Leaf Lesions
Leaf lesions usually develop after cankers form in spring and may continue to develop through summer and into fall. The lesions appear as bright yellow, angular spots on the upper surface of leaves. The lower surface of the leaves contains brown spore masses. A high incidence of early leaf infections may cause midseason defoliation and numerous fruit infections at harvest. Early and severe defoliation also may reduce yields and stimulate the production of new leaves and buds late in the growing season.

Fruit Lesions
Fruit lesions may develop during the growing season after leaf symptoms. They first develop as small, brownish spots (.1 inch) with green halos on mature, yellow fruit. When fruit reddens, lesion halos become greenish yellow. The lesions are sunken and extend several millimeters into the fruit.

COMMENTS ON THE DISEASE

Transchelia discolor survives in twig cankers or on other host parts, and airborne spores depend on wetness for infection. This disease typically has been more prevalent on cling varieties of peaches than on other varieties because the areas in which cling peaches are grown tend to have higher rainfall, making conditions more conducive to disease development. Fruit symptoms may resemble damage caused by stink bugs; confirm rust by the presence of rust spores within the fruit lesion or by leaf or twig symptoms.

MANAGEMENT

In orchards where rust develops it is managed with a fungicide treatment in spring. If the problem was severe the previous year, several fungicide treatments may be necessary in spring as soon as the trees leaf out. Because damp conditions favor rust development, angle sprinklers to avoid wetting the foliage. Drip irrigation is the least favorable to development of this disease because it doesn't increase the humidity in the orchard as much as flood or furrow irrigation.

Examine fruit on trees every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program (see FRUIT EVALUATION AT HARVEST). Record results for the harvest (115 KB, PDF) sample.

Organically Acceptable Methods
Sulfur treatments are acceptable for use in an organically certified crop.

Chemical Control
To be effective, treatments must be applied before rust symptoms appear on leaves. Examine one-year-old fruiting wood for small blisters or longitudinal splits. If twig cankers are found and rain is forecasted, make a treatment. If wet weather persists, additional applications may be necessary in late May or early June. Disease severity in the preceding year is an important factor in determining potential of disease during current year.

Treatment with sulfur is both cost-effective and efficacious. The sterol inhibitors are also efficacious but more expensive than the sulfurs.

Common name Amount to Use R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed within groups in order of usefulness in an IPM program, taking into account efficacy. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
SULFUR TREATMENTS
A. WETTABLE SULFUR# 18 lb/100 gal water see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
B. WETTABLE SULFUR#
  . . . PLUS . . .
  LIQUID LIME SULFUR# Label rates see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
C. LIQUID LIME SULFUR# 6 gal/100 gal water see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
D. SULFUR DUST# 50 lb/acre see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application.
 
STEROL INHIBITOR FUNGICIDES
A. TEBUCONAZOLE
  (Elite, etc. 45WP) 4–8 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 3 lb/acre/season.
 
B. PROPICONAZOLE
  (Bumper, Tilt) 4 oz/acre 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Maximum of 2 preharvest sprays.
 
C. METCONAZOLE
  (Quash) 3.5–4 oz/acre 12 14
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not make more than 3 applications/season.
 
STROBILURIN FUNGICIDE
A. AZOXYSTROBIN
  (Abound) 12.3–15.4 fl oz/acre 4 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than two applications before alternating with a fungicide that has a different mode of action group number.
 
B. TRIFLOXYSTROBIN
  (Gem) 3.8 oz 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
+ Restricted entry 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.
# 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 (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1,4,9,11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to a fungicide with a different mode of action Group number.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
Diseases
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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