Treatment Plan

On susceptible cultivars, and especially in wet seasons, managing Botrytis requires both cultural and chemical approaches. According to Cornell grape pathologist Wayne Wilcox, “Perhaps more than any other disease, consistent control of Botrytis requires the conscientious use of cultural management practices even when the best fungicides are applied.” Cultural practices include any practice that improves air circulation in the canopy, such as site selection; canopy management practices including pruning, shoot positioning, and cluster zone leaf removal; removal of old cluster stems during pruning that are sources of infection during the new season; avoiding excessive nitrogen fertilization; using loose-clustered clones and cultivars, and using techniques that aid in promoting loose clusters.

The timing of fungicide sprays depends on seasonal weather patterns. Potential timings of sprays include late bloom, pre-bunch close, verasion, and pre-harvest. All Botrytis fungicides have the potential for developing disease resistance. Effective fungicide programs use a rotation among effective chemistries including Pristine Fungicide (Resistance Group Numbers 7 and 11), Elevate 50WDG Fungicide (Resistance Group Number 17), Rovral Brand 4 Flowable Fungicide (Resistance Group Number 2), and Vangard WG Fungicide (Resistance Group Number 9). Switch 62.5WG is a combination product containing the same active ingredient in Vangard, plus an unrelated, Resistance Group 12 fungicide. Pristine controls other important diseases while the other products are only used to control Botrytis. While pesticide labels may permit up to 3 applications per year, it is highly recommended that applications of any specific Resistance Group fungicides be limited to one or two applications per season in rotation with other Botrytis fungicides.

Pristine Fungicide is a combination fungicide containing pyraclostrobin (Resistance Group 11) and boscalid (Resistance Group 17), both providing activity against Botrytis with a high risk of disease resistance development against this disease. Pristine also has activity against downy mildew, powdery mildew, black rot, anthracnose, Phomopsis, and “summer rots”, but powdery mildew and downy mildew resistance is well-documented where Pristine or other Resistance Group 17 fungicides have been applied for many years. Wayne Wilcox at Cornell indicates Botrytis control with Pristine is fair when used at 8 to 10.5 oz. per acre, good when used at 12.5 oz per acre, and very good to excellent when used at 19 oz per acre.   14 day PHI, 12 hr/5 day REI – see label for details.

Rovral Brand 4 Flowable Fungicide is very effective against Botrytis where disease resistance has not developed. It provides protectant, post-infection, and anti-sporulant activity with a high risk of disease resistance development. Apply Rovral at 1.5 to 2 pint per acre in a minimum of 50 gallons per acre, aiming the spray at the fruit zone. Addition of non-ionic surfactant or oil may improve performance. Spray solution should have a pH of 5-7; use a buffer if necessary as some chemical breakdown is likely to occur especially if spray solution is alkaline (pH above 7). Four applications are permitted by the label but it is highly recommended to limit applications of Rovral to one per season and make at least one application per season of an unrelated fungicide with good Botrytis activity. 7 day PHI, 48 hr REI.

Elevate 50 WDG is very effective against Botrytis, it provides protectant and post-infection activity against Botrytis with a moderate risk of disease resistance development and also provides modest suppression of powdery mildew. Apply Elevate at 1 lb per acre in at least 50 gallons per acre, aiming the spray at the fruit zone. Use in a rotational program with other Botrytis fungicides. Do not apply more than 2 consecutive applications of Elevate before switching to another effective Botrytis fungicide, and do not apply more than 3 lb Elevate per season. 0 day PHI, 12 hr REI.

Vangard WG Fungicide is very effective against Botrytis where disease resistance has not developed, it provides protectant, post-infection, and anti-sporulant activity with a moderate risk of disease resistance development. Apply Vangard at 10 oz per acre, aiming the spray at the fruit zone. Use in a rotational program with other unrelated Botrytis fungicides. 7 day PHI, 12 hr REI.