How to Manage Pests

UC Pest Management Guidelines

Almond

Powdery Mildew

Pathogens: thought to be Podosphaera (=Sphaerotheca) pannosa, Podosphaera tridactyla, and P. leucotricha

(Reviewed 3/09, updated 11/12)

In this Guideline:


SYMPTOMS AND SIGNS

Typical symptoms of powdery mildew include russeting on almond hulls. The symptoms are reminiscent of rusty spot on peach fruit caused by Podosphaera leucotricha but without the typical powdery white growth. No conidia (asexual spores) or chasmothecia (sexual fruiting structures of powdery mildew fungi) are generally observed on the fruit. Foliar and twig symptoms are absent.

COMMENTS ON THE DISEASE

Powdery mildew of almond has been only rarely reported in California and generally does not cause economic crop losses. Other crops such as peach have been reported to develop powdery mildew symptoms on fruit without reproductive structures forming in the infected areas. Podosphaera leucotricha, P. tridactyla, and Podosphaera (=Sphaerotheca) pannosa have been described on almond in California, as well as in other locations in the world. Growth of the pathogen is favored by cool, moist nights and warm days. Generally, fruit are susceptible only up to time of shell hardening, but later infections can occur on some varieties. Certain cultivars such as Mission, Padre, and Ruby are most susceptible.

MANAGEMENT

The disease is rarely an economic problem on almonds in California. If management of powdery mildew on almonds is needed, control practices should focus on protecting fruit from infections. Jacket-split (late petal fall) and mid-spring applications of powdery mildew fungicides are highly effective in managing the disease. Avoid growing almonds near apple varieties that are highly susceptible to powdery mildew, such as Jonathan, Gravenstein, and Rome Beauty. If nearby apples are expected to cause mildew problems on almonds, control the disease on apples.

Organically Acceptable Methods

Some sulfur sprays are acceptable for use in an organically certified crop.

Chemical Control

Generally, chemical control is not needed. If necessary, apply one of the fungicides listed below from jacket split until mid-April.

Common name Amount to Use R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
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 (PDF), and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. MYCLOBUTANIL
  (Rally 40W) 2.5–6 oz/acre 24 90
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation (sterol) inhibitor (3)
 
B. TEBUCONAZOLE/TRIFLOXYSTROBIN
  (Adament) 4.0-8.0 oz 12 60
  MODE OF ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3), Quinone outside inhibitor (11)
  COMMENTS: Do not make more than two successive applications, and no more than 4 per season, to limit the development of resistance.
 
C. 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 4 per season, to limit the development of resistance.
 
D. FLUOPYRAM/TRIFLOXYSTROBIN
  (Luna Sensation) 5.0-7.6 fl oz 12 60
  MODE OF ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7), Quinone outside inhibitor (11)
  COMMENTS: Do not make more than two successive applications, and no more than 4 per season, to limit the development of resistance.
 
E. 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 4 per season, to limit the development of resistance.
 
F. FLUOPYRAM/TEBUCONAZOLE
  (Luna Experience) 7.2-17.0 fl oz 12 35
  MODE OF ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7) and demethylation (sterol) inhibitor (3)
  COMMENTS: Do not make more than two successive applications and no more than 2 per season to limit the development of resistance.
 
G. 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 successive applications, and no more than 4 per season, to limit the development of resistance.
 
H. SULFUR DUST# Label rates See label 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application. Check with your certifier to determine which products are organically acceptable.
 
I. WETTABLE SULFUR# Label rates See label 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application. Check with your certifier to determine which products are organically acceptable.
 
J. WETTABLE SULFUR#   See label 0
  . . . PLUS . . .
  LIQUID LIME SULFUR# Label rates See label 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Do not apply within 3 weeks of an oil application. Check with your certifier to determine which products are 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 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

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

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