How to Manage Pests

UC Pest Management Guidelines

Grape

Botrytis Bunch Rot

Pathogen: Botrytis cinerea

(Reviewed 6/06, updated 2/14)

In this Guideline:


SYMPTOMS

Early-season shoot blight may occur following frequent spring rains. Flowers can become infected during bloom; generally the fungus then becomes dormant until late in the season when sugar concentration increases in the infected berry. The fungus then resumes growth and spreads throughout the berry. Infected berries split and leak, thus allowing the pathogen to grow and sporulate on berry surfaces and spread to adjoining berries by mid-season. Spores from infected fruit can directly infect intact, ripe berries as harvest approaches.

COMMENTS ON THE DISEASE

The fungus overwinters as sclerotia in berry mummies on the ground or left hanging on the vine and in canes. Germination and spore production occur in spring. Infections require free water for a definite period of time depending on temperature. Infections may occur during bloom should rains occur; preclose rachis infections often occur on Chardonnay. Late-season infections are most severe when relative humidity exceeds 92%, free moisture is present on the fruit surface, and temperatures are in the 58° to 82°F range. Berries that have been damaged by insects, birds, machinery, etc. may become infected at any time after the fruit begins to ripen because the juice in the berry can provide the necessary water and nutrients for fungal growth.

MANAGEMENT

Successful management of Botrytis bunch rot can be achieved through the use of several strategies. The efficacy of a fungicide depends on getting good coverage, and coverage is affected by the canopy and stage of growth. By employing cultural control methods, properly applying fungicides, and using resistant varieties, the disease can be managed.

Cultural Control

Excellent control has been achieved using canopy management and leaf removal in particular. Removal of basal leaves or basal lateral shoots at or immediately after berry set has resulted in significantly reduced incidence and severity of disease. In warmer growing areas, be careful not to remove excessive numbers of leaves, which can lead to sunburned fruit. This condition is made worse when leaves are removed later in the season. If leaves are removed at cluster set, the berries acclimate readily to the sunlight and develop a thick cuticle that helps prevent sunburn as well as Botrytis infection.

On cordon-trained vines, only remove leaves from the side of the vine that receives morning sun. Do not remove lateral shoots. If leaves are not removed and weather is dry in spring, one fungicide application should be made sometime between bloom and pea-size berries. Otherwise, apply sprays before rainfall especially at bloom or after veraison.

Northern and coastal production areas

Remove leaves or lateral shoots around clusters beginning at late bloom and continue to berry set.

Central Valley

Remove leaves (from bloom to berry set) or hedge (mid-season) to open canopy.

Organically Acceptable Methods

Canopy management and other cultural control methods along with sprays of Organic JMS Stylet Oil and Serenade are organically acceptable methods.

Monitoring and Treatment Decisions

Look for flagging shoot tips or entire shoots during rapid shoot growth. If you see flagging, attempt to break or cut the shoot in the region between the flaccid area and the adjacent area with normal turgor. Brown discoloration on the cut surface is evidence of Botrytis.

If the entire shoot is involved, look for a hole at the base, which could indicate feeding by branch and twig borer.

If basal leaves are not removed, apply fungicides before rain in northern and coastal production areas to prevent flower infections. Research data shows a trend toward better control if fungicides are applied at bloom, preclose, and veraison. If leaf removal is practiced, then sprays can be limited to one application if wet weather occurs during bloom (or none if no rain occurs). Thorough coverage is essential for all fungicide treatments.

A fungicide application may also be warranted if a major rain is expected late in the season when grapes are nearly mature. Otherwise, management of Botrytis bunch rot following bloom generally relies on proper cultural practices as outlined in SUMMER BUNCH ROT.

At harvest, check table grape for Botrytis symptoms to assess this year's management program and to plan for next year.

Common name Amount per acre** R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM Program, taking into account efficacy. Also consider the general properties of the fungicide as well as information relating to environmental impact.
 
Note: Treatments can be made in conjunction with plant growth regulators and other applications.
 
A. CYPRODINIL
  (Vangard WG) 10 oz 12 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 20 oz/acre per season. Rate is 5 to 10 oz if tank-mixed with another fungicide.
 
B. FENHEXAMID
  (Elevate 50WDG) 1 lb 12 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Hydroxyanilide (17)
  COMMENTS: Do not make more than two consecutive applications. Do not apply more than 3 lb a.i. product/acre per season.
 
C. PYRIMETHANIL
  (Scala SC) 18 fl oz 12 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 36 fl oz/acre per season. Rate is 9 fl oz if tank-mixed with another fungicide.
 
D. FLUOPYRAM + TEBUCONAZOLE
  (Luna Experience) 8–8.6 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (7) and Demethylation inhibitor (3)
  COMMENTS: For use on wine grapes only. Do not make more than two consecutive applications; rotate to a fungicide with a different mode of action. The R.E.I. is 5 days for treated grapes when conducting cane tying, turning, or girdling of wine grapes. Do not apply more than 34 fl oz/acre per season.
 
E. CYPRODINIL + FLUDIOXONIL
  (Switch 62.5WG) 11–14 oz 12 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) and Phenylpyrrole (12)
  COMMENTS: Do not apply in less than 21-day intervals. Do not make more than two consecutive applications; rotate to a fungicide with a different mode of action.
 
F. DIFENOCONAZOLE + CYPRODINIL
  (Inspire Super) 20 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) and Anilinopyrimidine (9)
  COMMENTS: Do not apply more than 2 consecutive applications; rotate to a fungicide with a different mode of action.
 
G. IPRODIONE
  (Rovral 4F) 1.5–2 lb 48 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
  COMMENTS: Do not apply more than 4 times per season. Addition of a narrow range oil (superior, supreme) at 1% increases the effectiveness of this fungicide.
 
H. PYRACLOSTROBIN + BOSCALID
  (Pristine) 23 oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) and Carboxamide (7)
  COMMENTS: Do not apply on Concord, Worden, Fredonia, Niagara, and related varieties. Do not make more than 2 consecutive applications; rotate to a fungicide with a different mode of action. The R.E.I. is 5 days when conducting cane tying, turning, or girdling.
 
I. NARROW RANGE OIL#
  (JMS Stylet) 1% 4 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): A contact fungicide with smothering and barrier effects.
  COMMENTS: Foliage burn may occur if oil is applied within 2 weeks of sulfur or captan sprays. Oil will temporarily remove the 'bloom' on the berries; to avoid this, do not spray within 2 weeks of harvest.
 
J. BACILLUS SUBTILIS#
  (Serenade Max) 1–3 lb 4 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Microbial (44)
 
** Apply with enough water to provide complete coverage.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the R.E.I. exceeds the P.H.I. The longer of two intervals is the minimum time that must elapse before harvest.
# Acceptable for use on organically grown produce.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different Group number are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

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 County
L. G. Varela, UC IPM Program, Sonoma County
S. Vasquez, UC Cooperative Extension, Fresno County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Research Center, Parlier
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
Acknowledgment for contributions to Diseases:
G. M. Leavitt, UC Cooperative Extension, Madera County

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