World Class. Face to Face. 2017 WSGS Grandview, WA 17 November 2017 GRAPE POWDERY MILDEW: MANAGEMENT AND RESISTANCE Michelle M. Moyer, Ph.D. Associate Professor Statewide Viticulture Extension Specialist WSU-IAREC Prosser, WA wine.wsu.edu
2017 FOR SOME
TOP 3 REASONS 2017 WAS A BAD MILDEW YEAR These are true for both wine grapes and juice grapes.
VINE DEVELOPMENT Vines grew fast this year Cold damage = latent and count bud break When 6 inches is really 12 inches
Graphs compiled by Lynn Mills, WSU-IAREC http://wine.wsu.edu/extension/weather WEATHER We had high late winter and early spring precipitation and higher humidity in June The year started off a little cool, but was overall average
SPRAY PRACTICES S-T-R-E-T-C-H-E-D spray intervals early season 15-21 day intervals on oil and sulfur Low-water volume usage on full canopies
BUT THAT S NOT ALL Yes, there is a 4 th reason.
POWDERY MILDEW IS STARTING TO CHANGE Vive La Résistance!
POINTS ABOUT RESISTANCE We ve only been able to verify resistance to FRAC 11 (strobilurin) fungicides Resistance has likely been here for a few years Warm, dry conditions in 2014-2016 likely masked disease development BUT, there were control failures in 2016 that were a little suspicious Most places that had mildew with resistance genes ALSO had other factors contributing to management failures
Figure courtesy Dr. Walt Mahaffee, USDA-ARS, Corvallis, OR THE WEST COAST STORY (THIS SPRING) E. necator QoI resistance in Oregon and Monterey County, CA vineyards
Table courtesy Dr. Walt Mahaffee, USDA-ARS, Corvallis, OR NOT JUST QOI The fungicide resistant make-up of E. necator isolates from Oregon QoI Resistant a Myclobutanil (Rally) DMI Resistant b Tebuconazole (Elite) Number of Isolates % of total sensitive sensitive sensitive 2 4% sensitive moderate sensitive 1 2% sensitive moderate moderate 3 6% resistant sensitive sensitive 2 4% resistant moderate sensitive 3 6% resistant moderate moderate 10 21% resistant resistant moderate 21 45% resistant resistant resistant 5 11% a Resistant to > 100 µl/ml of azoxystrobin (Abound) or trifloxystrobin (Flint) b Sensitive no sporulation at 0.5 µg/ml; Moderate-sporulation >0.5 µg/ml; Resistant sporulation > 3 µg/ml on treated leaf disks
241 samples tested in 2017 THE WASHINGTON STORY (END OF SEPTEMBER) Strobilurin Resistance Gene Frequency Grape Powdery Mildew (Washington) Resistance Gene No Resistance Gene Mix
BRIEF SUMMARY OF RESULTS Field-level resistance in potentially 96% of the vineyards evaluated Resistance found in vineyards bordering cherry and apple orchards Odd places for resistant gene detection: Some Concord blocks Some Organic blocks Young blocks (<5 years old)
UNDERSTANDING FUNGICIDES Nothing is a silver bullet except a silver bullet.
FUNGICIDES CLASSIFIED IN MANY WAYS Classification Scheme Trade Name Flint Rally Sulfur 1) Active Ingredient trifloxystrobin myclobutanil sulfur 2) Mode of action QoI DMI 3) Chemical group/class 4) Mobility in plant Locally systemic 5) Role in protection Protectant Multi-site contact strobilurin triazole sulfur Locally systemic Protectant and early infection Contact Protectant 6) Breadth of activity Single-site Single-site Multi-site 7) FRAC Code 11 3 M2
Image from: Deising, H.B. S. Reimann, and S.F. Pascholati. 2008. Brazil J Micro. 39:286-295. HOW FIELD RESISTANCE EMERGES Qualitative Resistance (FRAC 11) Quantitative Resistance (FRAC 3)
Wong and Wilcox. 1999. Plant Disease 86:394-404. NOTHING NEW Strobilurin resistance already in NY Azoxystrobin (QoI, FRAC 11) Labeled for use in 1997; resistance found in 1999 In vineyards where 15-20 applications had been made since introduction Note: typically more fungicide applications in NY than in WA Programs may include 4-6 (or more!) QoI applications in a single season Also noted partial cross-resistance with myclobutanil (DMI, FRAC 3)
SPRAY PRACTICES CAN INFLUENCE RESISTANCE WHERE WHEN HOW
MANAGING MILDEW With or Without Resistance
ALWAYS GOOD TIPS 1. Spray on-time o Starting early keeps the disease in-check o Not stretching intervals ensures tissue is protected 2. Follow label rates o Low rates encourage resistance development o Some products are ineffective at low rates 3. Pay attention to spray practices o Drive slow; spray every row o o Use enough water / don t spray in the wind Calibrate, Calibrate, Calibrate!
TANK-MIXING Tank-mixing involves applying 2 MOAs simultaneously in the field Some product formulations already do this for you Pristine, Unicorn, Inspire Super, etc. A cheap tank mix is the addition of sulfur (or another contact product) Example: 3-5 lbs sulfur Check for phytotoxicity Check for chemical incompatibility
CURRENT RECOMMENDATIONS FOR MANAGEMENT: 1. Consider an every-other-year rotation option 2. Use FRAC 11 fungicides early if you cannot avoid their use, and apply with a product of another mode of action 3. Avoid the use FRAC 11 fungicides going into prebloom and through bloom if you have had confirmed resistance in your vineyard.
Moyer, et. al. 2014. AJEV 65:315-324. PRE-SEASON ERADICATION VS. IN-SEASON MGMT Eradicating mildew before the season starts can help you if you do nothing else But you always do something else. Nothing beats a good in-season program Spend your money on starting early (3 shoot growth), than spraying with the snow Low-Pressure Year High-Pressure Year
HOW DO I KNOW IF I MIGHT HAVE A RESISTANCE ISSUE? We can help!
HELP WANTED Funded by Washington State Grape and Wine Research Program Sampling for resistance across WA (and OR, CA) Sampling canopy mildew in the summer Sampling cleistothecia in the fall / winter
THE KITS Kits contain 20 sampling bags: Collection bag Disposable forceps Tube w/ sticker
THE TECHNIQUES Find a mildew colony (shoot, leaf, cluster) Collect mildew using kit / Tough-Spot Place into prepared tube, then bag. Drop off at IAREC Label bag
QUESTIONS? VITICULTURE EXTENSION WASHINGTON STATE UNIVERSITY World Class. Face to Face. michelle.moyer@wsu.edu; Office: 509-786-9234 www.wine.wsu.edu/extension www.facebook.com/wsu.vit.enol.ext