How to Manage Pests

UC Pest Management Guidelines

Almond

Anthracnose

Pathogen: Colletotrichum acutatum

(Reviewed 8/17, updated 8/17)

In this Guideline:


SYMPTOMS AND SIGNS

Symptoms of anthracnose on almond include blossom blight and fruit infections often with spur and limb dieback. Infected flowers look similar to brown rot strikes. Leaves on infected spurs develop marginal necrosis, beginning with water-soaked areas that fade in color; leaves die but remain attached to branches.

Infected nuts show round, orangish, sunken lesions on the hull. These symptoms may appear about 3 weeks after petal fall; nuts remain susceptible and can be infected later in the season if conditions are favorable. Profuse gumming occurs as the infection progresses into the kernel. Diseased fruit die and turn into mummies that remain attached to the spur. The shoots or branches that bear infected nuts often die. Although the fungus may invade fruitwood, it is seldom cultured from affected branches. Death of the wood may result from a toxin rather than from direct colonization of the wood by the fungus.

COMMENTS ON THE DISEASE

All cultivars appear to be susceptible to anthracnose. The disease has been most damaging on Thompson, Merced, Price, Peerless, Winters, Monterey, Fritz, and Butte; moderate on Harvey, Carmel, NePlus Ultra, Padre, and Mission. Nonpareil is considered to be less susceptible. Ideal conditions for the development of this disease are warm, rainy weather.

MANAGEMENT

Fungicide treatment is the most important control strategy, but must be coupled with cultural practices to achieve the best control. In orchards that have a history of anthracnose, apply fungicide sprays beginning at 5-10% bloom or pink bud and repeat every 10 to 14 days if rains persist. Late spring rains may necessitate additional applications into May. Alternate materials as follows: make the first application at pink bud using either a demethylation (sterol) inhibitor (DMI; FRAC group 3) or quinone outside inhibitor (QoI; FRAC group 11) fungicide; follow this with a premixture (FRAC groups 3/11 or 7/11) fungicide application or a tank mix of captan or mancozeb mixed with iprodione or thiophanate-methyl applied at full bloom.

As long as conditions are conducive to disease development, alternate applications of demethylation (sterol) inhibitor (DMI), quinone outside inhibitor (QoI), captan, chlorothalonil, or mancozeb (FRAC Groups M3, M4, M5, 3, 11, respectively). Prune out dead, infected wood to reduce inoculum. If sprinkler irrigation is practiced, use low angle nozzles to prevent the tree canopy from being wetted by the sprinklers as a means of reducing disease spread.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees, and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
PINK BUD
 
A. PYRACLOSTROBIN/FLUXAPYROXAD
  (Merivon) 6.5 oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): quinone outside inhibitor (11) and succinate dehydrogenase inhibitor (7)
  COMMENTS: Do not make more than two successive applications, and no more than 3 per season, to limit the development of resistance.
 
B. PROPICONAZOLE
  (Bumper, Tilt) 8.0 oz 12 60
  MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
 
C. FLUOPYRAM/TRIFLOXYSTROBIN
  (Luna Sensation) 5.0-7.6 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7) and Quinone outside inhibitor (11)
  COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
 
D. METCONAZOLE
  (Quash) 3.5 oz 12 25
  MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
 
E. AZOXYSTROBIN
  (Abound) 12.0–15.5 oz 4 28
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than 2 sequential sprays before alternating with a fungicide that has a different mode of action. Do not apply more than four applications of strobilurin fungicides per year or apply more than 92.3 fl oz/acre per season.
 
F. AZOXYSTROBIN/DIFENOCONAZOLE
  (Quadris Top) 14 fl oz 12 28
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance.
 
G. TRIFLOXYSTROBIN
  (Gem 500SC) 2.9-3.8 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not make more than four applications per season and no more than two sequential sprays of QoI or SDHI fungicides to limit the potential for the development of resistance.
 
H. CHLOROTHALONIL
  (various) Label rates See label See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): Chlorinated hydrocarbon (M5)
  COMMENTS: Use as a multi-site protective treatment with long residual. Do not apply one week before or after a treatment containing oil or an oil-based pesticide.
 
BLOOM AND AFTER (as long as weather conducive)
 
A. PROPICONAZOLE
  (Bumper, Tilt) 8.0 oz 12 60
  MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance
 
B. FLUOPYRAM/TRIFLOXYSTROBIN
  (Luna Sensation) 5.0-7.6 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7), Quinone outside inhibitor (11)
  COMMENTS: Do not make more than two applications per season of QoIs or SDHIs to limit the potential for the development of resistance
 
C. METCONAZOLE
  (Quash) 3.5 oz 12 25
  MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two successive applications, and no more than four per season, to limit the development of resistance
 
D. AZOXYSTROBIN/PROPICONAZOLE
  (Quilt Xcel) 17.5-26.0 fl oz 12 60
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two applications per season of QoIs or SDHIs to limit the potential for the development of resistance.
 
E. TRIFLOXYSTROBIN
  (Gem 500 SC) 2.9-3.8 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not make more than four applications per season and no more than two sequential sprays of QoI or SDHI fungicides to limit the potential for the development of resistance.
 
F. PYRACLOSTROBIN/BOSCALID
  (Pristine) 10.5–14.5 oz 12 25
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and succinate dehydrogenase inhibitor (7)
  COMMENTS: Do not make more than four applications per season of (QoIs (strobilurins) or SDHIs and no more than two sequential applications before rotation to a different mode of action fungicide to limit the potential for the development of resistance.
 
G. CAPTAN
  (various) Label rates See label See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
 
H. ZIRAM
  (Ziram 76DF) 6–8 lb 48 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: When Ziram 76F is not applied as a tank mix with other systemic fungicides, use the maximum rate. Do not apply more than 32 lb of product/acre per season.
 
I. THIOPHANATE-METHYL
  (Topsin-M) 1.0-1.5 lb See label See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): methyl benzimidazole (1)
  COMMENTS: Do not apply more than 3 lb product per year. Some populations of the pathogen are not sensitive to MBC fungicides on almond in California.
 
J. MANCOZEB
  (Manzate Pro Stick) 4–6.4 lb See label See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): multi-site contact (M3)
 
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 action. 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.
QoI = quinone outside inhibitor or strobilurin
SDHI = succinate dehydrogenase inhibitor

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431

Diseases

J. E. Adaskaveg, Plant Pathology, UC Riverside
W. D. Gubler, Plant Pathology, UC Davis
R. A. Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Research and Extension Center, Parlier
B. A. Holtz, UC Cooperative Extension, San Joaquin County
F. P. Trouillas, Plant Pathology, Kearney Agricultural Research and Extension Center, Parlier

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