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How to Manage Pests
UC Pest Management Guidelines
Almond
Hull Rot
Pathogens: Rhizopus stolonifer and Monilinia spp.
(Reviewed 1/05,
updated 1/05)
In this Guideline:
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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.
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.
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. Not irrigating 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 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 Ne
Plus Ultra. Hard-shelled varieties such as Mission, Davey, and Drake may
exhibit rotted hulls but rarely shoot dieback.
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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
Acknowledgment for contributions to the disease section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier
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