How to Manage Pests

UC Pest Management Guidelines

Almond

Shot Hole

Pathogen: Wilsonomyces carpophilus

(Reviewed 3/09, updated 11/12)

In this Guideline:


SYMPTOMS AND SIGNS

Spots occur on leaves, fruit, twigs, and flowers; however, flower and twig lesions are relatively scarce or difficult to find. Leaf lesions begin as tiny reddish specks that enlarge by several millimeters into spots having tan centers and purplish margins. When the fungus sporulates, the fruiting structure appears as a small dark speck (the sporodochium and spores) in the center of the spot; this is a diagnostic characteristic of shot hole disease. Spots on young leaves usually fall out, leaving a hole (the shot hole); older leaves retain their lesions. Fruit spots are small with purplish margins, slightly corky, and raised. Spots are found on the upper surface of fruit with respect to the way it hangs on trees. Heavy infection of young fruit may cause fruit drop or distortion and gumming of fruit.

COMMENTS ON THE DISEASE

The fungus survives on infected twigs and as spores in healthy buds. Spores are moved by water to new sites; prolonged periods of wetness, either due to rain or sprinkler irrigation, are required for the disease to develop. Shot hole can cause losses in yield, defoliation, and weakened trees.

MANAGEMENT

Monitor orchards in fall and spring for shot hole lesions and fruiting structures. Fruiting structures appear in the center of leaf lesions as small black spots and can be seen with a hand lens. If fruiting structures are present in leaf lesions in fall, there is a high risk of shot hole development the following spring and a petal fall treatment should be applied. If fruiting structures are not present on leaf lesions in fall, the petal fall treatment will not be needed for shot hole. (It may be necessary for control of other diseases such as scab or leaf blight, however.)

Whether or not a petal fall treatment is applied, monitor leaves in spring for lesions with fruiting structures. As soon as fruiting structures are evident, apply a treatment; continue treatments at the recommended label interval as long as conditions are conducive to disease development. If fruiting structures are not present, a treatment is not required, but continue monitoring until weather conditions no longer are wet and conducive to shot hole development.

Contact fungicides serve as protectants, not eradicants, and provide control only if they are applied so foliage and fruit are well covered before a wet period. The minimum number of applications may vary each year, depending upon the rain pattern and use of sprinkler irrigation.

When zinc sulfate (20-40 lb/acre) is applied in late October to early November to hasten leaf fall, shot hole inoculum is prevented from increasing. Otherwise, high levels of inoculum may develop and overwinter on the trees, infecting leaves the following spring.

Common name Amount/Acre 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. FLUOPYRAM/TRIFLOXYSTROBIN
  (Luna Sensation) 5.0-7.6 fl oz 12 60
  MODE OF ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7) and Quinone outside inhibitor (11)
  COMMENTS: Do not make more than 2 applications per season of QoIs or SDHIs to limit the potential for the development of resistance.
 
B. 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 4 applications per season of QoIs or SDHI to limit the potential for the development of resistance.
 
C. IPRODIONE
  (Rovral 2F) 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 make more than 4 applications per season.
 
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 successive applications, and no more than 4 per season, to limit the development of resistance.
 
E. AZOXYSTROBIN/DIFENOCONAZOLE
  (Quadris Top) 14 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 4 per season, to limit the development of resistance.
 
F. FLUOPYRAM/TEBUCONAZOLE
  (Luna Experience) 6-8 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
  (Abound) 11–15.4 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 4 applications of strobilurin fungicides per year or apply more than 2.88 qt/product/acre/season.
 
H. TRIFLOXYSTROBIN
  (Gem) 3.8 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 hullsplit. 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.
 
I. CHLOROTHALONIL
  (Echo 720, etc.) Label rates See label See label
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
  COMMENTS: Do not apply one week before or after a treatment containing oil or an oil-based pesticide.
 
J. CAPTAN
  (various 50WP) Label rates See label See label
  (various 50WP)
  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.
 
K. ZIRAM 76DF 6-8 lb 48 0
  MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Do not apply more than 32 lb/acre/season or apply later than 5 weeks after petal fall.
 
+ 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.
# 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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