Treatment Plan

Phomopsis is most likely to be a problem when the Phomopsis fungus is allowed to build up on dead canes or pruning stubs and/or when early-season sprays for the disease are omitted or when sprays are not timed properly (i.e. before extended periods of rainfall) or are applied ineffectively (as in every-other row spraying). Cultural practices to reduce Phomopsis include removing diseased and dead canes and pruning stubs during pruning.

Mancozeb, Captan, and Ziram are the most effective sprays against Phomopsis and should begin as early as 1” shoot growth in vineyards with heavy inoculum pressure, and should not be delayed beyond 3-5” shoot growth when clusters first become visible and rachises are highly susceptible. Copper and sulfur are only weakly effective against Phomopsis. Early season applications of strobilurin (Group 11) fungicides, including Pristine Fungicide and Abound Flowable Fungicide, are only fairly effective, but they provide good additional protection of rachises and fruit when used during bloom or later. Phomopsis fruit infections can occur until inoculum from previous year’s infections are depleted at about the pea-sized berry stage.

Mancozeb is the active ingredient in Dithane F-45 Rainshield (liquid formulation) and Manzate Pro-Stick Fungicide (dispersible granules). Mancozeb products provide protectant control of Phomopsis as well as black rot, anthracnose, downy mildew, and angular leaf scorch, and are at low risk of developing disease resistance. The maximum allowance for all products containing mancozeb ranges from 18-19.2 lb of active ingredient per acre per season. At the maximum use rate, Dithane or Manzate Pro-Stick can be used up to six times per season, but not within 66 days of harvest. For applications at 1-5” shoot growth, apply 1.6 to 3.2 qt Dithane or 2-4 lb Manzate Pro-Stick; for applications at 10-12” shoot growth through the immediate pre-bloom spray, apply 2.4 to 3.2 qt Dithane or 3-4 lb Manzate Pro-Stick; for post-bloom sprays, apply 3.2 qt Dithane or 4 lb Manzate Pro-Stick. 66 day PHI, 24 hr REI.

Ziram 76DF Fungicide provides protectant control of black rot and Phomopsis, and suppression of downy mildew with low risk of disease resistance development. Ziram is similar to mancozeb products for control of black rot and Phomopsis, but less effective than mancozeb for control of downy mildew. Ziram can be used from 6” shoot growth until 21 days to harvest with a maximum 24 lb per acre per season; hence, Ziram is most useful where applications for control of black rot are needed within the 66 day PHI requirement for mancozeb products, or after the maximum seasonal use rate of mancozeb has been reached. Apply 3-4 lb Ziram for applications prior to bloom, and 4 lb Ziram for post-bloom applications. 21 day PHI, 48 hr REI.

Captan is the active ingredient in Captan 50 Wettable Powder, Captan 80 WDG, and Captec 4L. Captan products provide protectant control of Phomopsis, downy mildew, and “summer rots” but only suppression of black rot, with a low risk of disease resistance development. Early season sprays of Captan provide significant control of anthracnose but is not listed as a target on most product labels. Captan provides control of Phomopsis and downy mildew similar to that of mancozeb; however, mancozeb provides superior control of black rot to that of captan, so mancozeb is often the fungicide of choice for early season grape disease management programs. As mancozeb cannot be used within 66 days of harvest, captan can be an excellent choice for protective control of Phomopsis and downy mildew (and other diseases such as sour rots) later in the season. The total allowable use of captan from all products is 12 lb per acre per crop cycle, which is 6 applications at the maximum product use rate. For applications prior to the 10-12” growth stage, apply 2-4 lb Captan 50WP or 1.25 to 2.5 lb Captan 80WDG or 1-2 qt Captec 4L; for applications at 10-12” shoot growth or later, apply 3-4 lb Captan 50WP or 1.75 to 2.5 lb Captan 80WDG or 1.5 to 2 qt Captec 4L. 0 day PHI, 48 hr REI for Captan 50 Wettable Powder and Captec 4L, 0 day PHI, 72 hr REI for Captan 80 WDG.