How to Manage Pests

UC Pest Management Guidelines

Grape

Phomopsis Cane and Leafspot

Pathogen: Phomopsis viticola

(Reviewed 6/06, updated 2/14)

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 budbreak; 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. In table grapes, mark areas in the vineyard exhibiting poor budbreak in spring. Later examine these areas for disease symptoms. 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, and mancozeb 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 per acre** R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider the general properties of the fungicide as well as information relating to environmental impact.
 
DORMANT SEASON
 
A. LIQUID LIME SULFUR# Label rates See label See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  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 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Begin application at budbreak.
 
B. AZOXYSTROBIN
  (Abound) 11–15.4 fl oz 4 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Do not apply more than 3 sequential sprays; rotate 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 3–4 lb 4 days 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M4)
  COMMENTS: Captan-treated grapes are prohibited in Canada. Do not apply more than 24 lb/acre per year. Do not apply in combination with, immediately before, or closely following oil sprays.
 
D. MANCOZEB
  (Dithane M-45) Label rates 24 See comments
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Do not apply after fruit set or more than 7.5 lb/acre per season. Do not apply after bloom.
 
E. PYRACLOSTROBIN + BOSCALID
  (Pristine) 8–10.5 oz 24 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 sequential 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.
 
F. ZIRAM
  (Ziram 76DF) 3–4 lb 48 10
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Apply before buds swell and repeat after blossoming but before fruit forms. Do not apply after bloom.
 
G. LIME SULFUR Label rates 48 See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  COMMENTS: Apply as a directed spray in 80 to 100 gal water/acre. Apply in the delayed dormant period to kill spores.
 
H. SULFUR#
  (Golden Micronized Sulfur) 5 lb See comments See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M2)
  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.
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/.

[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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