Treatment Plan

Cultural practices that reduce the incidence of powdery mildew include planting varieties less susceptible to the disease and utilizing pruning and training practices that promote good light exposure throughout the canopy. Sprays to control powdery mildew may be needed as early as 3-5” shoot growth on V. vinifera and highly susceptible hybrids but are often delayed until the immediate pre-bloom stage on varieties only moderately susceptible to the disease. Sprays applied between immediate pre-bloom and fruit set are most important and should employ highly effective fungicides in a rotational program using full product rates, appropriate spray intervals, and good spray coverage. On highly susceptible cultivars protection through the bunch close stage is important as powdery mildew infections can promote the later development of bunch rots and/or wine spoilage, and sprays are often needed to protect foliage during the summer in order to obtain maximum fruit and wine quality. The powdery mildew fungus lives primarily on the surface of leaves, so products such as sulfur and spray oils can be used to suffocate or “burn out” existing infections; however, such eradicative applications require excellent spray coverage and are effective only against younger infections, and should not be counted upon to eradicate a full-blown epidemic. Synthetic fungicides are prone to disease resistance development and should be used in rotational programs that avoid the overuse of any chemical family and should be used primarily as protectants.

Vivando Fungicide (metrafenone is the active ingredient) is a very effective powdery mildew (only) fungicide that provides protectant, post-infection, and anti-sporulant activity with a moderate to high risk of disease resistance development. Vivando is unrelated to any other fungicide currently used in grapes so should be used in rotation with other effective powdery mildew fungicides. Do not make more than two sequential applications before alternating with another effective powdery mildew fungicide, and do not make more than three applications per season. The minimum interval between applications is 14 days. Apply 10.3 to 15.4 fl oz Vivando Fungicide per application. 14 day PHI, 12 hr REI.

Quintec (quinoxyfen is the active ingredient) provides excellent protectant control but no post-infection or eradicant control of powdery mildew (only), with moderate risk of disease resistance development. Quintec is unrelated to any other fungicide used in grapes in the U.S., so should be used in rotation with other effective powdery mildew fungicides with a maximum of 2-3 seasonal applications. Apply Quintec Fungicide at 3 to 4 fl oz per acre at no more than 14 day intervals. 14 day PHI, 12 hr REI.

The difenoconazole portion of Revus Top (a combination product with the unrelated fungicide manipropamid that controls downy mildew only), Mettle 125ME Fungicide (tetraconazole is the active ingredient), Rally 40WSP (myclobutanil is the active ingredient), and the tebuconazole products TebuStar 45WSP (water soluble packets), Amtide Tebuconazole 45WDG Fungicide (water dispersible granules) and Orius 20 AQ (liquid formulation) are fungicides with similar chemistry (DMI or sterol inhibitor fungicides, Resistance Group Number 3) with post-infection, anti-sporulant, and limited protectant activity with a moderate risk of disease resistance development. 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. In addition to powdery mildew, Revus Top is labeled for control of downy mildew (via the manipropamid component), black rot, and anthracnose; Mettle and Rally are labeled for control of black rot and anthracnose; and tebuconazole products are labeled for control of black rot. Apply 7 fl oz Revus Top or 3-5 oz Mettle or 4 oz TebuStar or 8.6 fl oz Orius 20 AQ or 4-5 oz Rally 40WSP. Use a non-ionic or penetrating surfactant such as Sure-Spred HV as per label instructions with Revus Top. 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 for all SI products listed; 12 hr REI for all SI products listed, except 24 hr REI for Rally 40WSP.

Abound Flowable Fungicide and the pyraclostrobin component of Pristine Fungicide are strobilurin (Resistance Group Number 11) fungicides that provide protectant, some post-infection, and anti-sporulant disease control with a moderate to high risk of disease resistance development. Pristine and Abound control powdery mildew, downy mildew, black rot, and Phomopsis. Pristine also controls Botrytis (at higher rates than are needed for powdery mildew control) while Abound provides suppression only. Pristine also provides very good control of anthracnose, bitter rot and ripe rot. Pristine contains an unrelated, Resistance Group 7 fungicide, boscalid, 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, Abound and 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 or alternated with unrelated fungicides. For powdery mildew control, apply Abound at 10-15.5 fl oz or Pristine at 8 to 12.5 oz. Higher rates may be needed for control of other diseases. Do not use Pristine on Concord or Noiret as it causes injury. Use Pristine with caution on Steuben, Rougeon, Worden, Fredonia, Niagara and related varieties where injury has occurred irregularly. 14 day PHI, 4 hr REI for Abound Flowable Fungicide; 14 day PHI, 12 hr/5 day REI for Pristine Fungicide – see label for details. 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.

JMS Stylet Oil (paraffinic oil) is a post-infection, anti-sporulant, eradicant fungicide with modest protectant activity and low risk of disease resistance development. JMS Stylet Oil provides significant eradicant activity against powdery mildew infections (only), but as a contact fungicide, thorough spray coverage is essential. Protective activity is 3 to 7 days following application but is mostly lost after as little as ¼” rain. Two or more applications of JMS Stylet Oil near veraison consistently lower Brix values by 1˚ to 2˚ at harvest. Do not spray oils when air temperature is above 85-90˚F as burning may occur. Do not use captan with or following an oil spray. Do not apply sulfur within 10 days of an oil application. Do not use oil and copper together with fruit present. Do not mix JMS Stylet Oil with certain nutrient spray materials or spreader-stickers as per label instructions. JMS Stylet Oil is most useful when combined with a protectant fungicide as the first powdery mildew spray of the season when disease infections may have already occurred or when they first become visible. Apply JMS Stylet Oil as a 1-2% solution (1 to 2 gallons per 100 gallons spray mix). 0 day PHI, 4 hr REI.

Microthiol Disperss (elemental sulfur) provides control of powdery mildew (only) with protectant, post-infection, anti-sporulant and some eradicant activity. Sulfur is subject to wash-off by rainfall. Do not apply sulfur within 10-21 days of an oil application (refer to specific product labels for restrictions) as injury may occur. Some native and hybrid cultivars can be injured by sulfur, refer to the Grapevine Variety Characteristics Chart

for varietal sensitivity. The regular use of sulfur during the season tank mixed with other effective powdery mildew fungicides on varieties highly susceptible to powdery mildew but not sensitive to sulfur application can eradicate young powdery mildew infections as they occur and is considered an effective disease resistance management practice. Apply 3 to 10 lb Microthiol Disperss per acre per application. 0 day PHI, 24 hr REI.

Nutrol (the active ingredient is monopotassium sulfate) is a potassium salt with post-infection, anti-sporulant, limited eradicant, and no protective activity against powdery mildew (only) with low risk of disease resistance development. Significant post-infection activity occurs when applied after the start of infections, during which time the infections are not yet visible. Nutrol has been relatively ineffective at eradicating well-established powdery mildew infections. Nutrol is most effective when applied sequentially with short (7-day) intervals, and can be useful when tank mixed with other effective powdery mildew fungicides. Apply 5 to 10 lb Nutrol per acre using a maximum 3 lb product per 10 gallons spray mix. For best results apply with a non-ionic surfactant such as Induce. 0 day PHI, 4 hr REI.

Copper fungicides provide 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 copper 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.