How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

The first indication of hull rot usually comes several weeks before harvest, when leaves on a shoot wither and die. Closely examine fruit on this shoot for a brown area on the outside of the hull and either tan fungal growth in the brown area on the inside or outside of the hull (this indicates Monilinia) or black fungal growth on the inside of the hull (this indicates Rhizopus). Fungi invade hulls and produce a toxin that kills the shoot attached to the fruit. Because the shoot is killed other green fruit on the shoot don't mature and they remain on the tree after harvest. The disease causes dieback of shoots and fruiting wood that reduce productivity in future years.

COMMENTS ON THE DISEASE

Almond hulls are susceptible to hull rot fungi from the beginning of hull split until the hulls dry—a period that can last from 10 days to 2 months depending on fertilization and irrigation.

MANAGEMENT

Look for nuts or leaves stuck on trees well after harvest as an indication of hull rot infections. No fungicides are suggested for hull rot. Irrigation management is the most important cultural control. Regulated deficit irrigating (255 KB, PDF) or reducing irrigation at the onset of hull split greatly reduces incidence of hull rot. Avoid standing water at hull split. Fertilizer management is also important; avoid excess nitrogen fertilizer. Take leaf samples in July to be sure nitrogen levels, which should be below 2.6%, don't favor hull rot.

Almond varieties vary in their susceptibility. The most susceptible varieties are Nonpareil, Kapareil, Sonora, Jordanolo, and IXL. Although frequently affected by hull rot, damage tends to be minimal on Merced, Thompson, and NePlus Ultra. Hard-shelled varieties such as Mission, Davey, and Drake may exhibit rotted hulls but rarely shoot dieback.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Diseases
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
B. A. Holtz, UC Cooperative Extension, Madera County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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