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How to Manage Pests
UC Pest Management Guidelines
Grape
Summer Bunch Rot (Sour Rot)
Pathogens: Aspergillus niger, Alternaria tenuis, Botrytis cinerea, Cladosporium herbarum, Rhizopus arrhizus, Penicillium sp., and others
(Reviewed 6/06,
updated 6/06)
In this Guideline:
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As berries ripen and sugar content exceeds 8%, injured fruit become
increasingly susceptible to invasion by a wide variety of naturally-occurring
fungi. Invasion occurs at the point of injury caused by insect or bird feeding,
mechanical or growth cracks, or lesions resulting from powdery mildew or black
measles (esca). The resulting rot can be severe as it progresses beyond the
original injury. Masses of black, brown, or green spores develop on the surface of infected
berries.
Bunch rot often culminates in sour rot, especially in the central and southern
San Joaquin Valley. Sour rot is caused by a variety of microorganisms,
including acetic acid bacteria, which are spread by vinegar flies attracted to
the rotting clusters.
Rotting fruit clusters present during veraison are indicative of
summer bunch rot. Management of this disease complex is based on reducing
injury or damage to the fruit, thus preventing invasion by bunch rot organisms.
Basal leaf removal at or after berry set has given excellent control of summer
bunch rot in the San Joaquin Valley. In warmer growing areas, be careful not to
remove excessive numbers of leaves, which can lead to sunburned fruit. Remove
leaves only from the side of the vine that receives afternoon shade. Also,
leafhopper populations and damage caused by omnivorous leafroller have been
reduced by this cultural practice. Treat at preclose and veraison if summer
bunch rot has been a problem in the past.
To reduce growth-related damage to the berries, follow proper
irrigation, fertilizer, fruit thinning, and canopy management practices. Prune
to achieve vine balance between vegetative growth and cluster number. Also
control powdery mildew and damaging populations of omnivorous leafroller and
other berry feeders.
| Common name |
Amount/Acre** |
P.H.I.+ |
| (trade name) |
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(days) |
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| When choosing a pesticide, consider information relating to environmental impact.
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| A. |
IPRODIONE |
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(Rovral) 4F |
1.5–2 lb |
7 |
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MODE OF ACTION: A dicarboximide (Group 2)1
fungicide.
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COMMENTS: Restricted entry interval: 48
hours. Combinations of iprodione mixed with copper can be effective against summer bunch rot. |
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UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Diseases
W. D. Gubler, Plant
Pathology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma Co.
L. G. Varela, UC IPM Program, Sonoma Co.
J. J. Stapleton, UC IPM Program, Kearney Agricultural Research Center,
Parlier
G. M. Leavitt, UC Cooperative Extension, Madera Co.
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
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