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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Brown rot infection on petals.

Almond

Brown Rot Blossom Blight

Pathogen: Monilinia laxa; rarely Monilinia fructicola

(Reviewed 3/09, updated 3/09)

In this Guideline:

SYMPTOMS

Young blossom spurs and associated leaves collapse to form shoot blight. Gum may exude at the base of infected flowers. Cankers on blighted twigs have tan centers with dark margins. At high humidity, gray to tan spore masses form on diseased flower parts and twig cankers.

Flowers may become infected from pink bud to petal fall and are most susceptible when fully open. In almonds, stigma, anthers, and petals are all very susceptible to infection.

COMMENTS ON THE DISEASE

The fungus survives in twig cankers and on remaining diseased flower parts and spurs. Spore pads (sporodochia) appear on these structures in late winter to provide inoculum for spring infection. Spores are airborne or rain splashed. Infection is favored by rainy weather with temperatures in the mid-70s during bloom. It can also occur in dry years with high humidity.

MANAGEMENT

Control is based upon protection of flower parts. Ideally, applications should be made for each cultivar according to its stage of bloom. Otherwise, timing should be determined by the bloom of the most seriously affected cultivar in the orchard.

Treat at pink bud (5-10% bloom) and/or full bloom. One application at full bloom is sufficient in most orchards in most years if there is no rain. If brown rot has been severe or in years of extended bloom accompanied by rainfall, a second or even third application near full bloom may be necessary.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
When choosing a pesticide, consider the general properties of the fungicide as well as information relating to fungicide resistance and environmental impact.
 
A. PYRIMETHANIL/TRIFLOXYSTROBIN
  (Distinguish) 12.8–26 fl oz 12 60
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) and Quinone outside inhibitor (11)
  COMMENTS: Do not apply after hull split.
 
B. FENBUCONAZOLE
  (Indar) 75WSP 1.25–2 oz 12 160
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Use allowed under a supplemental label.
 
C. PROPICONAZOLE
  (Orbit) 4–8 fl oz 12 60
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
D. PYRACLOSTROBIN/ BOSCALID
  (Pristine) 10.5-14.5 oz 12 25
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
  COMMENTS: Do not make more than 4 applications per season of strobilurins or carboxyanilides to limit the potential for the development of resistance.
 
E. IPRODIONE
  (Rovral) 4F 1 pt 24 0
  MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
  COMMENTS: Addition of a narrow range oil (superior, supreme) at 1 to 2% volume/volume increases the effectiveness of this material. Do not apply oil, however, within 3 weeks of a sulfur application or closely before or after an application of captan or chlorothalonil. Do not apply more than 4 applications/season.
 
F. PYRIMETHANIL
  (Scala) SC 9–18 fl oz 12 30
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
 
G. THIOPHANATE-METHYL
  (Topsin M) 70WP 1.5–2 lb 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
  COMMENTS: Strains of brown rot pathogen resistant to thiophanate-methyl have been found on almond, but resistance is not widespread. Do not apply more than 3 lb/season/acre.
 
H. CYPRODINIL
  (Vangard) WG 5 oz 12 60
  MODE OF ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 30 oz/acre/crop/year.
 
I. AZOXYSTROBIN
  (Abound) 2F 12.3–15.4 oz 4 28
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than 3 sequential sprays before alternating with a fungicide that has a different mode of action. Do not apply more than 4 applications of strobilurin fungicides/year or apply more than 2.88 qt/product/acre/season.
 
J. FENHEXAMID
  (Elevate) 50 WDG 1–1.5 lb 12 0
  MODE OF ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
  COMMENTS: Apply in sufficient water to obtain complete coverage of flowers and twigs. Do not make more than 2 consecutive applications or apply more than 6 lb/acre/season.
 
K. TRIFLOXYSTROBIN
  (Gem) 4–6 oz 12 60–see comments
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply within 60 days of harvest or after hull split. Do not exceed more than 3 applications of all strobilurins per season to limit the potential for the development of resistance. Do not apply more than 12 oz/acre/season.
 
L. MYCLOBUTANIL
  (Laredo) EC 8–12.8 fl oz 24 90
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Apply in 400 gallons water/acre. Do not make more than 3 applications or apply more than 38.4 fl oz/acre/season.
 
M. CAPTAN
  (various) 50WP 8 lb 4 days see label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
  COMMENTS: Preharvest interval varies depending on formulation and if hulls are to be fed to livestock. Do not apply in combination with, immediately before, or closely following oil sprays.
 
N. MANEB
  (various) Label rates 24 145
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Do not apply more than 32 lb of product/acre/season.
 
+ 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 these two intervals is the minimum time that must elapse before harvest may occur.
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: Almond
UC ANR Publication 3431
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
Roger Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center
B. A. Holtz, UC Cooperative Extension, Madera County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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