How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

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, Monterey, and Butte; moderate on Harvey, Carmel, NePlus Ultra, Fritz, Peerless, 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. 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 azoxystrobin or myclobutanil; follow this with a boscalid/pyraclostrobin application or a tank mix of captan or maneb mixed with iprodione or thiophanate-methyl applied at full bloom. As long as conditions are conducive to disease development, alternate applications of azoxystrobin or myclobutanil with boscalid/pyraclostrobin, captan, or maneb. Pruning out infected wood to reduce inoculum may also help.

More information on almond fungicides

• General properties
• Efficacy on almond diseases
• Treatment timing

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Disease
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
Acknowledgment for contributions to the disease section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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