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UC Pest Management Guidelines


Brown rot twig blight.

Prune

Brown Rot Blossom and Twig Blight

Pathogens: Monilinia laxa and Monilinia fructicola

(Reviewed 6/06, updated 4/09)

In this Guideline:


SYMPTOMS AND SIGNS

Blossom and twig blight cause the collapse of young blossom spurs and associated leaves. A gummy exudate is present at base of flowers. Gray brown spore masses develop on diseased flowers under high humidity. Cankers form on the wood at the base of blossom spurs.

COMMENTS ON THE DISEASE

The fungus survives in mummies, twig cankers, and remaining diseased flower parts and spurs. Spore pads (sporodochia) on old infections also may provide inoculum for spring infection. Spores are airborne or rain splashed. Optimum conditions for infection and disease development are rainy weather during bloom with temperatures in the mid-70s (0F). All flower parts are susceptible to infection, and these infections may lead to blossom blight.

MANAGEMENT

Unlike brown rot on peach and nectarine, control of spring brown rot of prune does not appear to have any effect on harvest levels of brown rot. However, in orchards with chronic blossom and twig blight, spring applications are recommended.

Cultural Control
Good orchard sanitation helps reduce the amount of brown rot inoculum in spring. Have pruning crews remove all fruit mummies and blighted shoots. Remove the mummies from the orchard and destroy them. If left on the orchard floor, mummies will produce inoculum in the spring. You can cultivate the orchard floor to bury fruit mummies and reduce inoculum production. Dense ground cover maintained during bloom favors the production of inoculum by fruit mummies.

Chemical Control
Treat at green bud and again at full bloom. An intermediate treatment at the popcorn stage may be necessary if bloom is prolonged and weather favors disease development. Fungicides are most effective when applied before a rainfall and allowed to dry.

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. PROPICONAZOLE
  (Orbit) 3.6EC 4 fl oz/acre 24 0
  (Bumper) 41.8EC 4 fl oz/acre 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Most effective when applied before a rainfall and allowed to dry. Apply at 5–10% bloom and make a second application at 80–100% bloom.
 
B. PYRACLOSTROBIN/BOSCALID
  (Pristine) 10.5–14.5 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
 
C. CYPRODINIL
  (Vangard) 75WG 5 oz 12 2
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 10 oz/acre/year for blossom blight control.
 
D. PYRIMETHANIL
  (Scala) SC 18 fl oz 12 2
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 10 oz/acre/year for blossom blight control.
 
E. IPRODIONE
  (Rovral) 4F 1–2 pt/acre 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
  COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material and will aid in aphid control.
 
F. THIOPHANATE METHYL
  (Topsin-M) 70WP 8 oz/100 gal water 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENTS: Addition of a narrow range oil (superior, supreme) at 1–2% increases the effectiveness of this material and will aid in aphid control. Strains of Monilinia fructicola resistant to thiophanate methyl have been found in California. If resistance has occurred in your orchard, do not use this fungicide. Use only 1 application of thiophanate methyl/year, and always apply with a fungicide of different chemistry.
 
G. FENHEXAMID
  (Elevate) 1–1.5 lb/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
  COMMENTS: Apply when conditions favor disease development. Do not apply more than 6 lb/acre/season.
 
H. MYCLOBUTANIL
  (Rally) 40W 2.5–6 oz 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 2.75 lb/acre/season.
 
I. CAPTAN 50WP
  (Various) 4–6 lb 4 days 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
  COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
 
J. CHLOROTHALONIL
  (Echo 720, Bravo Weather Stik) 3.125–4.125 pt/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays. Do not use after jacket split.
 
K. AZOXYSTROBIN
  (Abound 2F) 12.3–15.4 fl oz 4 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than 2 applications before alternating with a fungicide that has a different mode of action.
 
+ 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.
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 fungicide with a different mode of action Group number.

[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
W. H. Olson, UC Cooperative Extension, Butte County
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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