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How to Manage Pests

UC Pest Management Guidelines

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Phomopsis leafspot foliage symptoms.

Grape

Phomopsis Cane and Leafspot

Pathogen: Phomopsis viticola

(Reviewed 6/06, updated 6/06)

In this Guideline:

SYMPTOMS

Phomopsis cane and leafspot appears as tiny dark spots with yellowish margins on leaf blades and veins. Spots first show 3 to 4 weeks following rain. Leaf death may occur if large numbers of spots build up. Basal leaves with heavy infection become distorted and usually never develop to full size. On shoots, small spots with black centers similar to those found on leaves occur usually on a basal portion of the shoot. After spots lengthen a few millimeters, the epidermal layers of the shoots usually crack at the point of infection. Heavy infection usually results in a scabby appearance of the basal portions of the shoot. On clusters, spots similar to those that occur on shoots occur on the flower cluster stems.

Lesions on leaves, shoots, and clusters become inactive during the summer heat but rain just before harvest can cause light brown spots on clean berries and spots quickly enlarge and become dark brown. Berries may shrivel and become mummified. Infected canes appear bleached during the dormant season. Severely affected canes or spurs exhibit an irregular dark brown to black discoloration intermixed with whitish bleached areas. The black specks visible in the bleached areas are pycnidia that develop during the dormant season.

COMMENTS ON THE DISEASE

This disease is most severe in northern grape-growing regions (North Coast and northern San Joaquin Valley) where spring rains are common after bud break; moisture is required for infection. Infections generally occur when shoots begin to grow. Spores are released in large quantities from the overwintering pycnidia on diseased canes and spurs. These are splashed by rain onto early developing shoots and infection occurs when free moisture remains on the unprotected green tissue for many hours.

MANAGEMENT

Spur and cane lesions provide most of the inoculum for new infections. Reducing the source of the disease is important. A treatment of liquid lime sulfur before rainfall in fall will reduce the viability of pycnidia as well as reduce overwintering Botrytis sclerotia and powdery mildew spores.

In all areas, spring foliar treatments are advisable if rainfall is predicted after budbreak. Apply materials before the first rain after budbreak and before 0.5 inch shoot length (and again when shoots are 5 to 6 inches in length). Contact materials such as copper, sulfur, ziram, mancozeb, and maneb must be reapplied after significant rainfall in order to protect shoots up to 18 inches in length. If several rains are predicted, use systemic fungicides (azoxystrobin and kresoxim-methyl).

Common name Amount/Acre** P.H.I.+
(trade name)   (days)
The following materials are listed in order of usefulness in an IPM program taking into account efficacy. When choosing a pesticide, also consider information relating to environmental impact.
 
DORMANT SEASON
A. LIQUID LIME SULFUR#
Label rates
  
  MODE OF ACTION: A multi-site contact (Group M)1 inorganic fungicide.
  COMMENTS: Reduces overwintering structures of Phomopsis as well as Botrytis and powdery mildew spores.
 
SPRING FOLIAR TREATMENT
A. KRESOXIM-METHYL    
  (Sovran)
3.2–4.8 oz
14
  MODE OF ACTION: A Qol (Group 11)1 fungicide.
  COMMENTS: Restricted entry interval: 12 hours. Begin application at budbreak.
 
B. AZOXYSTROBIN    
  (Abound) F
11–15.4 fl oz
14
  MODE OF ACTION: A Qol (Group 11)1 fungicide.
  COMMENTS: Restricted entry interval: 4 hours. A strobilurin fungicide. Do not apply more than 3 sequential sprays before alternating with a fungicide that has a different mode of action. Apply before disease development begins. Follow label directions, especially as they pertain to number of applications allowed per year.
 
C. CAPTAN 50WP
2 lb
  
  MODE OF ACTION: A multi-site contact (Group M)1 phthalimide fungicide.
  COMMENTS: Restricted entry interval: 4 days. Captan-treated grapes prohibited in Canada. Do not apply more than 24 lb/acre/year. Do not apply in combination with, immediately before, or closely following oil sprays.
 
D. MANEB 80WP
1.5–2.5 lb
see comments
  MODE OF ACTION: A multi-site contact (Group M)1 dithiocarbamate fungicide.
  COMMENTS: Restricted entry interval: 24 hours. Do not apply after bloom.
 
E. MANCOZEB    
  (Dithane M-45)
Label rates
 see comments
  MODE OF ACTION: A multi-site contact (Group M)1 dithiocarbamate fungicide.
  COMMENTS: Restricted entry interval: 1 day. Do not apply after fruit set or more than 7.5 lb/acre/season. Do not apply after bloom.
 
F. PYRACLOSTROBIN/BOSCALID    
  (Pristine)
8–10.5 oz
14
  MODE OF ACTION: A Qol (Group 11)1 and carboxamide (Group 7)1 fungicide.
  COMMENTS: Restricted entry interval: 24 hours. Do not apply on Concord, Worden, Fredonia, Niagara, and related varieties. Do not make more than 2 sequential applications before rotating to a fungicide with a different mode of action.
   
G. ZIRAM    
  (Ziram) 76DF
3–4 lb
  
  MODE OF ACTION: A multi-site contact (Group M)1 dithio-carbamate fungicide
  COMMENTS: Restricted entry interval: 48 hours. Apply before buds swell and repeat after blossoming but before fruit forms.
 
H. LIME SULFUR
15–20 gal
  
  MODE OF ACTION: A multi-site contact (Group M)1 inorganic fungicide.
  COMMENTS: Restricted entry interval: 2 days. Apply as a directed spray in 80–100 gal water/acre. Apply in the delayed dormant period to kill spores.
 
I. SULFUR#    
  (Micronized Dry Flowable)
6 lb
  
  MODE OF ACTION: A multi-site contact (Group M)1 inorganic fungicide.
  COMMENTS: In some counties there is a 3-day restricted entry period when using sulfur; consult your county agricultural commissioner. Apply just before or immediately after post budbreak rains. Do not apply within 3 weeks of an oil application.
 
 
**  Apply with enough water to provide complete coverage.
+ Preharvest interval. Do not apply within this many days of 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/.

More information on grape fungicides

[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 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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