Treatment Plan

There is a wide range of susceptibility to downy mildew among grapevine cultivars. Vineyard practices that improve air circulation and speed drying time will help to control downy mildew. On most cultivars grown in humid climates, properly timed fungicide applications are necessary to manage the disease. Management programs for downy mildew should focus on preventing early season establishment of the disease that can cause cluster destruction from pre-bloom through early post-bloom growth stages, and to limit secondary spread on the foliage during summer and fall. Protective fungicides may need to be applied as early as 2-3 weeks before bloom on susceptible cultivars if the weather is wet. In any case sprays should not be delayed beyond the immediate pre-bloom stage. Research at Cornell University indicates fruit is no longer susceptible to infection at about 4 weeks post-bloom, but foliar infections can occur into early autumn. Mancozeb, captan, and copper fungicides provide excellent protective (only) control activity with little to no risk of disease resistance development. Ziram is another protectant fungicide but only provides suppression of downy mildew. Strobilurin fungicides are protective fungicides absorbed into grapevine tissue, but are at high risk of resistance; Pristine Fungicide and Abound Flowable Fungicide provide excellent control of downy mildew. Other fungicide classes offer a range of protective and systemic (curative) activity, and all are at moderate to high risk of disease resistance development. Effective management programs for downy mildew utilize these products in an integrated approach that discourages the buildup of resistant downy mildew by rotating among available chemistries and avoiding the overuse of any chemistry.

Mancozeb is the backbone of early-season disease management programs in grapes as it controls downy mildew, black rot, Phomopsis, and anthracnose with low risk of disease resistance development. Mancozeb is the active ingredient in Dithane F-45 Rainshield (liquid formulation) and Manzate Pro-Stick Fungicide (dispersible granules). 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. As a general rule of thumb, one half of a mancozeb product will be washed off following one inch of rain. For use prior to bloom, apply 2.4 to 3.2 qt Dithane or 3-4 lb Manzate Pro-Stick. For post-bloom applications, apply 3.2 qt Dithane or 4 lb Manzate Pro-Stick. 66 day PHI, 24 hr REI for listed mancozeb products.

Captan provides control of 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 downy mildew (and other diseases such as sour rots) later in the season. Captan is the active ingredient in Captan 50 Wettable Powder, Captan 80 WDG, and Captec 4L. 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 immediate pre-bloom spray, apply 2-4 lb Captan 50 Wettable Powder or 1.25-2.5 lb Captan 80 WDG or 1-2 qt Captec 4L; for immediate pre-bloom applications apply 3-4 lb Captan 50 Wettable Powder or 1.75-2.5 lb Captan 80 WDG or 1.5-2 qt Captec 4L; for post-bloom sprays, apply 4 lb Captan 50 Wettable Powder or 2.5 lb Captan 80 WDG or 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.

Copper fungicides provide good control of downy mildew similar to that of mancozeb and captan; only fair control of black rot; and some control of powdery mildew – adequate on cultivars only moderately susceptible to powdery mildew, but typically not adequate on V. vinifera and other susceptible varieties. Some varieties are sensitive to copper injury, but varietal sensitivity is not known or not published for many cultivars.   Lime is often added to copper fungicide applications to reduce the chance of foliar injury. Lime should not be used in a tank mix with captan or carbaryl. Do not use copper on varieties with unknown sensitivity – conduct small scale spray trials to determine the likelihood of injury. Spray water with low pH increases the chance of injury, add lime especially if water pH is 6.0 or less. Copper applied under slow drying conditions may cause injury on otherwise tolerant varieties. Copper is sometimes used as the last spray of the season to control downy mildew and suppress powdery mildew under moderate pressure but is solely a protectant fungicide and does not “burn out” previous infections; however, disease resistance development is not an issue when applying copper onto existing infections. Apply 0.75 to 1.75 lb DuPont Kocide 3000 (dry flowable formulation of copper hydroxide) or 1.33 to 2.66 pint Champ Formula 2 Flowable (liquid formulation of copper hydroxide); add lime as per label directions. 0 day PHI, 48 hr REI.

Revus Fungicide (active ingredient mandipropamid) is a Resistance Group Number 40 fungicide unrelated to other fungicides (except Revus Top) registered for use in vineyards. It is absorbed by plant tissues and provides excellent control of downy mildew (only) with post-infection, anti-sporulant and residual protective activity with moderate risk of disease resistance development. Use in a rotational program with other downy mildew fungicides making no more than two consecutive applications before switching to another effective downy mildew fungicide, and no more than four applications per season. Apply Revus Fungicide at 8 fl oz per acre. 14 day PHI, 4 hr REI.

Revus Top is a pre-mix of mandipropamid (the active ingredient in Revus Fungicide), a Resistance Group 40 fungicide, and difenoconazole, a sterol inhibitor (DMI) Resistance Group 3 fungicide. The mandipropamid component of Revus Top is absorbed by plant tissues and provides excellent control of downy mildew (only) with post-infection, anti-sporulant and residual protective activity, with moderate risk of disease resistance development. The difenoconazole portion of Revus Top controls powdery mildew and black rot. Powdery mildew resistance to the DMI fungicides is a common problem where they have been used in the past, in which case they are less effective than they were in the past and should not be relied upon as the primary tool for management of powdery mildew. They continue to be valuable in rotational programs with other fungicides, but rotating with other DMI fungicides is not an effective resistance management approach. Wayne Wilcox (Cornell University) recommends limiting the total number of DMI fungicide applications to no more than 3 per year; applying full rates with good coverage; using early in the season and post-bloom while avoiding use when more than a modest amount of powdery mildew is present; and maintaining 14 day spray intervals. Apply Revus Top at 7 fl oz and add a non-ionic or penetrating surfactant such as Sure-Spred HV. Do not use Revus Top on Concord, Concord Seedless, and Thomcord (causes injury) and use caution when applying on V. labrusca, V. labrusca hybrids, and other non-vinifera hybrids where sensitivity is not known – the use of Revus Top by itself or in tank mixtures with materials that may increase uptake (adjuvants, foliar fertilizers) may result in leaf burning or other phytotoxic effects. 14 day PHI, 12 hr REI.

Pristine Fungicide is a pre-mix of two unrelated fungicides. The pyraclostrobin component of Pristine is a strobilurin (Resistance Group Number 11) fungicide that provides protectant, some post-infection, and anti-sporulant control of downy mildew with a moderate to high risk of disease resistance development. Pristine also controls powdery mildew, black rot, anthracnose, Phomopsis, and Botrytis (at higher rates than are needed for powdery mildew control), bitter rot and ripe rot. The other component of Pristine is boscalid, an unrelated, Resistance Group 7 fungicide that controls powdery mildew and Botrytis with a moderate risk of disease resistance development.   Although labeled for use starting at the 3-5” shoot growth stage Pristine should be saved for the immediate pre-bloom or later sprays. Powdery mildew and downy mildew resistance to the strobilurin fungicides has occurred in many vineyards following several years of repeated use. It is highly recommended that the combined use of all strobilurin fungicides including Abound and Pristine be limited to no more than 2 applications per season and rotated, alternated, and/or tank-mixed with other unrelated fungicides that also control downy (and powdery) mildew. 14 day PHI, 12 hr/5 day REI – see label for details.

Abound Flowable Fungicide is a strobilurin (Resistance Group Number 11) fungicide the provides protectant, some post-infection, and anti-sporulant control of downy mildew with a moderate to high risk of disease resistance development. Abound also controls powdery mildew, black rot, and Phomopsis and provides suppression of Botrytis. Use of strobilurin fungicides such as Pristine and Abound are generally saved for the immediate pre-bloom or later sprays. Powdery mildew and downy mildew resistance to the strobilurin fungicides has occurred in many vineyards following several years of repeated use. It is highly recommended that the combined use of all strobilurin fungicides including Abound and Pristine be limited to no more than 2 applications per season and rotated, alternated, and/or tank-mixed with other unrelated fungicides that also control downy (and powdery) mildew. 14 day PHI, 4 hr REI. IMPORTANT NOTE: Abound is EXTREMELY phytotoxic to certain apple varieties. Do not spray Abound where spray drift may reach apple trees. Do not use spray equipment which has been previously used to apply Abound to spray apple trees, as even trace amounts can cause unacceptable phytotoxicity to certain apple and crabapple varieties.

Ranman Fungicide (active ingredient cyazofamid) is a Resistance Group Number 21 fungicide that provides good to very good control of downy mildew (only) with protectant and anti-sporulant activity and perhaps limited post-infection activity. Ranman is unrelated to other fungicides used in grapes, providing an additional option for control of downy mildew in rotational programs. Tank mixing with a phosphorous acid product such as Phostrol has provided excellent control in University trials, presumably by adding significant post-infection activity. Apply Ranman at 2.1 to 2.75 fl oz per acre and observe label restrictions for alternating with other fungicides. 30 day PHI, 12 hr REI.

Phostrol Agricultural Fungicide (active ingredient phosphorous acid) is a Resistance Group Number 33 fungicide that controls downy mildew (only) and provides moderate protectant, post-infection, and anti-sporulant activity with a moderate risk of disease resistance development. Phostrol is very active when applied 3-5 days after the beginning of an infection period, but has only limited protective activity, so spray intervals should not exceed 10 days during periods of wet weather. Due to the risk of disease resistance development, do not apply more than twice in a row before using a different downy mildew fungicide, and do not apply more than four times per season. Some varieties may be susceptible to foliar injury, the label advises to test for varietal sensitivity prior to use. Apply 2.5 to 5 pint Phostrol Agricultural fungicide per acre. 0 day PHI, 4 hr REI.

Ridomil Gold MZ WG is a premix of mefanoxam (Resistance Group Number 4) and mancozeb. Mefanoxam provides protectant, post-infection, and anti-sporulant activity against downy mildew (only) with a high risk of disease resistance development. Downy mildew resistance to mefanoxam can develop quickly when the product is used intensively, so mancozeb is included in Ridomil Gold MZ to decrease the likelihood of resistance development. At the labeled rate of 2.5 lb, Ridomil Gold MZ provides the same amount of mancozeb as 2 lb per acre Manzate Pro-Stick or 1.6 qt Dithane F-45 Rainshield. Supplement with additional mancozeb up to the maximum use rates of Manzate Pro-Stick or Dithane if control of black rot and Phomopsis is desired. Do not use more than two applications of Ridomil per season. Apply Ridomil Gold MZ WG at 2.5 lb per acre. 66 day PHI, 48 hr REI.