Agriculture: Almond Pest Management Guidelines

Brown Rot Blossom Blight

Symptoms and Signs

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, determine timing by the bloom of the most seriously affected cultivar in the orchard.

Treat at pink bud (5–10% bloom) and full bloom. One application at full bloom is sufficient in most orchards in most years if there is low rainfall. 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.

Cultivars highly susceptible to brown rot include Drake, Winters, and Wood Colony; other cultivars such as Butte, Carmel, and Ne Plus Ultra are very susceptible.

Common name Amount per acre REI‡ PHI‡
(Example trade name) (hours) (days)
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
A. PYRACLOSTROBIN/FLUXAPYROXAD
(Merivon) 5–6.5 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 three applications per season or 19.5 fl oz/acre 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. FENBUCONAZOLE
(Indar 2F) 4–6 fl oz 12 160
MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
D. DIFENOCONAZOLE/CYPRODINIL
(Inspire Super) 16.0-20.0 fl oz 12 60
MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3) and anilinopyrimidine (9)
E. DIFENOCONAZOLE
(Inspire) 7 fl oz 12 14
MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
F. 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.
G. 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.
H. FLUOPYRAM/TEBUCONAZOLE
(Luna Experience) 6.0–17.0 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 two per season to limit the development of resistance.
I. AZOXYSTROBIN/PROPICONAZOLE
(Quilt Xcel) 14.0–26.0 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 four per season, to limit the development of resistance.
J. 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.
K. PYRACLOSTROBIN/BOSCALID
(Pristine) 10.5–14.5 oz 12 25
MODE-OF-ACTION GROUP NAME (NUMBER1): succinate dehydrogenase inhibitor (7) and Quinone outside inhibitor (11)
COMMENTS: Do not make more than four applications per season of QoIs 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.
L. IPRODIONE
(Rovral, Nevado) 1 pt 24 See comments
MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
. . . PLUS . . .
NARROW RANGE OIL
(various) Label rates See label See label
MODE-OF-ACTION: Contact
COMMENTS: Do not apply iprodione (Rovral, Nevado) later than 5 weeks after petal fall. 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.
M. PYRIMETHANIL
(Scala SC) 9–18 fl oz 12 30
MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
N. THIOPHANATE-METHYL
(Topsin M WSB) 1.5 lb 72 (3 days) See label
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 product/season per acre.
O. CYPRODINIL
(Vangard WG) 5 oz 12 60
MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
COMMENTS: Do not apply more than 30 oz/acre per crop per year.
P. 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 two 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.
Q. FENHEXAMID
(Elevate 50 WDG) 1–1.5 lb 12 See comments
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 two consecutive applications or apply more than 6 lb/acre per season. Apply up to 28 days after petal fall.
R. TRIFLOXYSTROBIN
(Gem 500SC) 3.8 oz 12 14
MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
COMMENTS: Do not apply within 14 days of harvest or after hullsplit. 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.
S. MYCLOBUTANIL
(Laredo EW, Rally 40WSP) Label rates 24 90
MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3)
COMMENTS: Apply in 400 gallons water/acre. Do not make more than two successive applications and no more than three per season to limit the development of resistance. Use in rotation with different FRAC groups.
T. CAPTAN
(various 50WP) Label rates See label See label
MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
COMMENTS: Do not apply in combination with, immediately before, or closely following oil sprays.
U. TEBUCONAZOLE
(Toledo, Tebucon) 4–8 oz 12 35
MODE-OF-ACTION GROUP NAME (NUMBER1): demethylation (sterol) inhibitor (3).
COMMENTS: Do not make more than two successive applications and no more than four applications per season to limit the development of resistance.
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
Text Updated: 08/17
Treatment Table Updated: 08/17