How to Manage Pests

UC Pest Management Guidelines


Leaf curl symptoms on leaves and young twigs.

Nectarine

Peach Leaf Curl

Pathogen: Taphrina deformans

(Reviewed 6/10, updated 5/12)

In this Guideline:


SYMPTOMS AND SIGNS

Leaves produced in spring are thickened, curled, and colored red or yellow instead of normal green. Severely affected shoots die. Irregular, reddish lesions are sometimes seen on fruit. Badly diseased leaves fall by early summer, and repeated infections debilitate trees and kill branches.

After fall and winter rains, spores (blastospores) of the fungus may be observed as a white bloom on the surface of leaves and be found on twigs, buds, and inbetween bud scales.

COMMENTS ON THE DISEASE

Taphrina deformans survives on tree surfaces and buds and is favored by cool wet weather during spring. The pathogen most likely survives the warm, dry summer period as ascospores. With fall and winter rains, the ascospores germinate and form numerous budding blastospores. Tree to tree spread of the pathogen occurs by airborne ascospores, which can move longer distances or by blastospores that are disseminated in splashing water. Leaves and the occasional fruit infections occur only on young plant tissue.

MANAGEMENT

Peach leaf curl can be a serious problem, especially on many of the low-chilling varieties and when spring weather is unusually wet. Annual management is recommended. To successfully control the disease, treatment timing is crucial. This disease is usually kept under control with a dormant fungicide application, but in wet years more than one spray application may be needed.

Organically Acceptable Methods
Spraying with Bordeaux mixture or copper is acceptable in an organically certified crop.

Chemical Control
Most copper products have long residual activity, even during prolonged wetness. Therefore, one application in the dormant/delayed dormant period is sufficient except in areas of high rainfall or where leaf curl has become an increasing problem. In such cases, an added application at delayed dormancy in late winter or before bud swell is recommended. Recently, formulations of fixed coppers have been developed with reduced metallic copper equivalent (MCE). Residual activity is very important to control peach leaf curl and these products, when lower rates are used (e.g., 1.2 to 2.1 lbs/A MCE for reduced MCE fixed coppers, compared to 3 to 5 lbs/A MCE for fixed coppers or even 8 to 10 lbs/A MCE for basic copper sulfate), have not been as efficacious over long rainy winter seasons.

If using the newer reduced MCE products

  • always use the upper label rate,
  • consider using a sticker or winter oil as an adjuvant to increase persistence, and
  • plan to make two applications.

Several other fungicides that are equivalent or even more effective than copper for managing peach leaf curl are ziram, chlorothalonil (Echo or Bravo), and dodine (Syllit) when applied at the optimal time. Ziram is most effective.

  1. Apply in late November/early December after most leaves have fallen from trees to ensure excellent coverage of branches, stems, and buds and before significant late fall and winter rainfall occurs. (This spray will also control shot hole (Wilsonomyces carpophilus).
  2. Apply an additional January/early February treatment if high rainfall occurs in December and early January.
  3. In addition to January/early February treatments, apply during pre-bloom (at bud swell or two weeks before bloom) if high rainfall occurs in February.

To increase fungicide persistence of the materials, use an adjuvant such as an oil or a sticker.

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 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.
 
A. ZIRAM 76DF 6-8 lb/acre – high precipitation fall/winter
4-6 lbs/acre – low precipitation fall/winter
48 30
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact, Dithiocarbamates (M3)
  COMMENTS: While not a preferred timing, if heavy rains are occurring as leaves are emerging in spring or disease symptoms are present, an application of ziram can be beneficial in helping to reduce the spread of the fungus. Apply treatments at a minimum of 100 gals water/A. Higher gallonage (120-150 gals/A) generally improves coverage.
 
B. FIXED COPPER#
  (various products) Label rates see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact, Inorganic metal (M1)
  COMMENTS: Not all copper compounds are approved for use in organic production; check product.
 
C. CHLOROTHALONIL
  (Echo 720) 3.125–4.125 pt/acre 12 NA
  (Bravo Ultrex DF) 2.8-3.8 lb/acre 12 0
  (Bravo Weather Stik) 3.125–4.125 pt/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact, Isophthalonitriles (M5)
  COMMENTS: Do not use with or closely following oil sprays. Plan to make at least two applications in northern nectarine production areas of California where higher rainfall occurs. A single application may be sufficient in southern nectarine growing districts of California. Apply treatments at a minimum of 100 gals water/A. Higher gallonage (120-150 gals/A) generally improves coverage.
 
D. BORDEAUX MIXTURE#
  10:10:100 Label rates see label see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact, Inorganic metal (M1)
  COMMENTS: For information on making Bordeaux mixture, see UC IPM Pest Note: Bordeaux Mixture, ANR Publication 7481. Check copper label to determine if organically acceptable.
+ 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.
NA Not applicable.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Nectarine
UC ANR Publication 3451
Diseases
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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