Managing Fungal Pathogens of Grapevines in the Texas Hill Country

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1 Managing Fungal Pathogens of Grapevines in the Texas Hill Country Jim Kamas Asst. Professor & Extension Specialist Texas A&M AgriLife Extension Service Viticulture & Fruit Lab Fredericksburg, Texas

2 Keys to Effective Grape Fungal Disease Management Keeping Disease Inoculum Low Understanding Pathogen Life Cycle Pathogen, Weather, Seasonality Selecting the Right Product(s) for Control Timing Spray Applications Efficiently Making Spray Applications Effectively Managing Fungicide Resistance

3 Focus on the 4 Major Fungal/Fruit Diseases Powdery Mildew Downy Mildew Black Rot Phomopsis

4 Critical Elements in Fungal Disease Management Understand the pathogen biology Environmental effects When active Cultural practices that favor/ disrupt Understand host susceptibility Relative degree (cultivar effect) When not susceptible Critical, peak period Understand fungicide characteristics Surface-active or penetrant? Protectant? Post-infection? Eradicant? Spectrum of activity Resistance concerns and management

5 Phomopsis

6 Phomopsis viticoli Cool, Wet Season Disease Overwintering Structures Latent Rachis Infections Infections Become Systemic

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8 Phomopsis Cane & Leaf Spot in Texas Very Subtle Cane Lesions Infection Takes Place VERY Early Becomes a Problem With Extended Hang Time Berry Sporulation Has Been Observed, But is Uncommon Collapsing Rachis is Most Common Symptom

9 Leaf Symptoms Can Vary

10 Look For Basal Cane Lesions and Rachis Lesions

11 Phomopsis on Berries

12 Management of Phomopsis Start Spray Program at 1-3 Shoot Growth Must Maintain Coverage As Shoots & Cluster Tissue Expands Berries Susceptible to Direct Infection Until Pea-Sized Rachis Tissue is Usually Most Critical In Minimizing Crop Loss

13 Black Rot

14 Black Rot Overwinters as Mummified Fruit or Cane Lesions Infection Periods are Temperature and Leaf Wetness Driven Key Periods of Susceptibility 2 Weeks Pre-bloom to 30 Days Post-bloom Achilles Heel of Organic Grape Production

15 Black Rot Management Considerations Most commercial vineyards have low levels of inoculum If so, makes it much easier to control with limited number of sprays Serious economic losses usually result from berry-to-berry spread within the vine (rainsplashed secondary spores) 2015 Season Has Changed the Paradigm in Many Younger Vineyards

16 Black Rot Life Cycle

17 Leaf wetness duration and temperature necessary for infection by the black rot fungus. Temperature (degrees F) Hours of leaf wetness required for infection Monitoring Black Rot Infection Periods 45 No infection

18 BLACK ROT: IMPORTANCE OF SANITATION (Removal of mummies from trellis) Mummies in trellis (versus on the ground) Produce spores until +/- veraison vs. 1-2 wk postbloom Produce 10-20x as many spores over the season Produce spores right next to new fruit (splash dispersal)

19 Bl Wayne Wilcox NYSAES

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21 BLACK ROT: LENGTH OF INCUBATION PERIOD Need to know to determine, What went wrong? 2-3 weeks when berries are young 3-5 weeks as berries become resistant

22 Wayne Wilcox NYSAES

23 Powdery Mildew

24 Powdery Mildew Problematic in All Parts of the State 0.1 Rain & 50 F Needed for Primary Infection No Rainfall Needed for Secondary Infection Key Period of Susceptibility is 2 Weeks Pre-bloom to 30 Days Post-bloom

25 Powdery Mildew Lifecycle

26 Powdery Mildew Lifecycle

27 POWDERY MILDEW: EFFECT of TEMPERATURE on DISEASE SPREAD Temp. ( F) Generation time (days) not active

28 Potential Losses from PM Direct Fruit Loss Loss of Fruit Quality Loss of Photosynthetic Area

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30 Importance of Canopy Management Superior Canopy Management Provides Environment Less Susceptible to Disease Outbreak Direct Effect of Ultraviolet Light

31 Powdery Mildew Rescue Treatments Excellent Tank Mix Additions to Conventional Fungicides Important Products for Late Season (Post-harvest) Control of PM DO NOT WANT TO SOLELY RELY ON THEM WHEN SUSCEPTIBLE FRUIT IS PRESENT If Used Alone, Complete Coverage is Absolutely Essential!

32 Downy Mildew

33 Downy Mildew Overwinters in Leaf Litter on Vineyard Floor Spores Disseminated by Splashing Rain Primary Infection Takes Place During Wet Nights Fruit/Rachis Infections Become Systemic

34 Downy Mildew Life Cycle

35 Potential Losses from Downy Mildew Direct Fruit Loss Loss of Photosynthetic Area (Foliage) Loss of Fruit Quality

36 Downy Mildew Management Considerations First primary infections occur about 2-3 weeks before bloom, to ~ 2 weeks post-bloom 52 F, 0.1 rain Critical time to prevent epidemic from starting Young Clusters Highly Susceptible

37 Anthracnose Occurs Annually in The Gulf Coast Can Be Found in Hill Country in Very Wet Years (Especially on Blanc du Bois )

38 Anthracnose Management Dormant Treatments With Calcium Polysulfide (Limed Sulfur) Very Effective Other Material Efficacy???

39 Leaf Blight Pseudocercospora vitis OR Isariopis clavispora Imperfect stage of Mycosphaerella personata

40 Leaf Blight Can Show You Different Looks

41 Other Things To Worry About. Aspergillis Vine Canker

42 Aspergillis- Opportunistic Wound Pathogen

43 Bunch Rot Organisms

44 Botrytis cinerea Although the fungus grows well only in berries that are ripening, young fruit also can become infected through attached blossom parts, and perhaps through scars left by the fallen caps. Such infections remaining latent (dormant) until some of them resume activity and rot the berries as they start to ripen.

45 Characteristics of Other Bunch Rots & Molds Alternaria alternata Aspergillis niger Organisms are Ubiquitous Opportunistic Invaders Often Enter Through Mechanical Injury GBM Hail Bird Pecks PM Infections Cracking Due to High Moisture Status Cladosporium spp.

46 Variety Selection? Irrigation Strategy? Other Organisms Material Selection & Timing Penicillium spp. Greeneria uvicola Rhizopus spp. Bitter Rot Conventional Wisdom is that Multi-site Toxin Fungicides are the Best Materials Available for Control

47 Other Things You Might See Xanthamonas leaf spot Rupestris speckle Septoria leaf spot

48 Periods of Greatest Fruit/ Rachis Infection Potential Blackrot Powdery Downy Phomopsis Leaf Blight?????????????????????? Bunch Rots????????????????????? Budbreak Pre-bl Bl.-Shatter Pea Berry Véraison Harvest

49 There Is No Recipe For Disease Free Fruit

50 Keys to Successful Disease Management *Site Selection *Sanitation *Canopy Management *Fungicide Applications *Manage Resistance

51 2014 Release From Texas A&M Press