How to Manage Pests

UC Pest Management Guidelines

Plum

Brown Rot Blossom and Twig Blight

Pathogens: Monilinia laxa and Monilinia fructicola

(Reviewed 5/06, updated 4/09)

In this Guideline

SYMPTOMS AND SIGNS

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

COMMENTS ON THE DISEASE

Monilinia spp. survive on diseased twigs and mummified fruit. Its development is favored by moderate temperatures and moist-to-wet conditions during bloom or on mature fruit. The disease is not common on most plum cultivars because unlike peach and nectarine, many plums are less susceptible to brown rot blossom and twig blight, as well as fruit rot. For late-season cultivars, if an orchard has a history of the disease, or if rainfall occurs before harvest on mature fruit, protective fungicide treatments may be necessary to prevent brown rot of fruit. Late-season cultivars with harvest dates in August or September include Angeleno, Autumn Beaut, Betty Ann, Casselman, Howard Sun, and Rosemary.

MANAGEMENT

Sanitation includes removal and destruction of mummified fruit from trees and orchard floors after harvest and before bloom, as well as heavily thinned fruit from orchard floors that may be colonized by the pathogen and function as a source of inoculum during fruit maturation. On susceptible cultivars, apply a protective fungicide treatment as a delayed bloom application (20-40% full bloom). A second application may be necessary during protracted flowering or during foggy or rainy weather. Protective fungicide treatments to prevent fruit brown rot are usually not needed on early or mid-season varieties. As discussed above for late-season cultivars, if an orchard has a history of the disease, or if rainfall is forecasted on mature fruit in the harvest period, protective fungicide treatments may be necessary to prevent brown rot of fruit.

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 quality. 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. Do not apply to "Stanley" type plums.
 
B. IPRODIONE
  (Rovral) 4F 1–2 lb/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.
 
C. THIOPHANATE METHYL
  (Topsin-M) 70WP 8 oz/100 gal water 12 1
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENTS: 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.
 
D. PYRACLOSTROBIN/BOSCALID
  (Pristine) 10.5–14.5 oz/acre 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
 
E. PYRIMETHANIL
  (Scala) SC 18 fl oz 12 2
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
 
F. 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.
 
G. 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.
 
H. 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.
 
I. 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.
 
J. 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: Plum
UC ANR Publication 3462

Diseases

W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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