Grape Disease Management

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Grape Disease Management

• By Harold Larsen

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Primary Grape Diseases

• Powdery mildew
• Crown gall
• Bunch rot
• Grapevine leafroll virus (GLRV)

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Grape Powdery Mildew

• Caused by fungus, Uncinula necator
• Reduces yield, vigor
• Reduces berry quality for wine
• Reduces vine and bud hardiness

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Powdery Mildew - Symptoms

• Powdery mycelium on shoots, leaves, berries
• Russet stunting of berries
• Rusty spots on canes
• Flagged shoots (in spring, infected buds)
• Cleistothecia in fall on infected tissues
  (leaves, shoots, canes)

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Powdery Mildew - Leaves
Image at web site http//www.apsnet.org/online/f
eature/pmildew/galery.htm/img02.htm
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Powdery Mildew - Colonies
Image at web site http//www.apsnet.org/online/fe
ature/pmildew/gallery.htm/img01.htm
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Powdery Mildew Flagged Shoots
Image at website http//www.apsnet.org/online/fea
ture/pmildew/gallery.htm/img08.htm
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Powdery Mildew - Conidia
Image at web site http//www.apsnet.org/online/fe
ature/pmildew/gallery.htm/img07.htm
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Powdery Mildew on Fruit
Image at web site http//www.apsnet.org/online/fe
ature/pmildew/gallery.htm/img04.htm
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Powdery Mildew - Cleistothecia
Image at web site http//www.apsnet.org/online/fe
ature/pmildew/gallery.htm/img06.htm
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Powdery Mildew Fruit Russet
Image at web page http//www.apsnet.org/online/fe
ature/pmildew/gallery.htm/img05.htm
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Powdery Mildew Cane Scarring
Image at web site http//www.apsnet.org/online/fe
ature/pmildew/gallery.htm/img03.htm
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Powdery Mildew Disease Factors

• Cultivar susceptibility
• Availability of newly grown tissue
• Temperature
• Humidity / rainfall
• Inoculum source

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Cultivar Susceptibility

• High Carignane, Thompson Seedless, Ruby
  Seedless, Cardinal, Chardonnay, Cabernet
  Sauvignon, Chenin Blanc
• Moderate White Petite Sirah, Zinfandel,
  Semillon, Riesling

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Tissue Susceptibility

• New shoots / leaves
• New fruit
• (All tissues that lack well developed cuticle)

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Temperature

• Mild weather favors powdery mildew (64o 84o F,
  optimum 77o F)
• Spores germinate _at_ 43o to 91o F
• Extended exposure to temperatures of 92o F or
  more kills spores and mildew colonies
• 12 hrs exposure to UV light temperature of 95o
  F kills the fungal colonies completely

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Humidity / Rainfall

• Spores can germinate at humidities as low as 20,
  but 40 or more results in better germination
• 12 15 hrs of continuous leaf wetness is needed
  at temperatures of 50o 59o F
• Dew formation also is adequate for spore
  germination if it occurs early enough in the
  evening (providing a long enough leaf wetness
  period)

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Inoculum Source

• Infected buds (result in flagged shoots in
  spring)
• Overwintering cleistothecia
• Conidia from infected vines (or other hosts)
  nearby can include Virginia creeper, Boston
  ivy, and monks hood vine.

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Control Considerations

• Fungus can develop resistance to control
  materials, so need to minimize risk of this
• Many categories of control materials are
  available
• Materials also differ in how long they are
  effective after application
• Need to rotate chemistries or tank mix different
  chemistries

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Control Strategies

• Use predictive models to determine need for
  sprays
• Wait until see first infection, then apply
  eradicative materials (Stylet oil, or jojoba oil)
  
• Start early, keep regular, rotate chemistries
• Use sulfur on 7 10 da intervals (until veraison)

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Chemical / Control Categories

• Sulfurs (organic certification programs)
• Sterol inhibitors (DMIs)
• Strobilurins (new class of fungicides)
• Oils (some are eradicative)
• Potassium bicarbonate
• Biological control agents (mildew pathogens)
• Plant defense elicitors (new class)
• Mycophagous mites

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Chemistry Groups - Sulfurs

• Wettable powders (8595 _at_ 5 lb/acre)
• Flowable formulations (6F 6 lbs / gal. _at_ 7
  pts/acre prebloom, 1 gal/acre postbloom)
• Micronized formulations (DF, e.g. Thiolux 80DF _at_
  2-5 6 lbs/acre)
• surfactant

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Chemistry Groups DMIs

• Bayleton 50DF (_at_ 2-6 oz/acre)
• Nova 40W (_at_ 3-5 oz/acre)
• Procure 50W (_at_ 4-8 oz / acre)
• Rubigan 1E (_at_ 2-3 fl. oz./acre prebloom, 4-5
  fl. oz./ acre postbloom, 5-6 fl. oz./ acre
  summer)
• surfactant

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Chemistry Groups - Strobilurins

• Flint 50WDG (_at_ 2 oz./acre)
• Abound 2.08F (_at_ 11.0 15.4 fl. oz./acre)
• Sovran 50WDG (_at_ 3.2-4.8 oz./acre)

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Chemistry Groups - Oils

• Stylet oil _at_ 2 soln.
• Jojoba oil (EcoErase _at_ 2 soln.

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Chemistry Groups - Bicarbonates

• Potassium bicarbonate (Kaligreen 2.5 5 lb /
  acre)

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Chemistry Groups - Plant Defense Elicitors
(Experimental)

• Serenade (_at_ 6 lb / acre)

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Biological Controls

• Ampellomyces quisquallis (AQ10 _at_ 0.5 1 oz/acre)
• Mycophagous mites (potential future option)

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Example Control Program

• 2 shoot growth Sulfur _at_ 4 lb ai / acre
• 4 6 shoot growth DMI (Nova _at_ 5 oz/acre)
• 12 - 14 Strobilurin (Flint _at_ 2
  oz/acre)
• Flowering DMI (Nova _at_ 5 oz/acre)
• Flowering 14 da Strob. (Flint _at_ 2 oz/acre)
• Flowering 28 da sulfur _at_ 4 lb ai/acre
• Monitor planting Stylet oil as needed (_at_ 1.5
  solution)
• Annual Cost approx. 110 / acre / season

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Crown Gall
Image at web page http//www.ipm.ucdavis.edu/PMG/
r302100911.html
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Crown Gall

• Caused by bacterium, Agrobacter tumifasciens
  (actually by phage within A. tumifasciens)
• Bacterium enters by wounds, dumps the phage into
  the cells, leaves
• Phage then inserts self into cell DNA
• Result is tumor-like growth in host plant

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Crown Gall
Images at web page http//www.cas.psu.edu/docs/CA
SDEPT/plant/fpath/grape/crgall.html and
http//www.ipm.ucdavis.edu/PMG/A/D-GR-ATUM-TR.002
.html
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Crown Gall

• Control by Galltrol (Agrobacter radiobacter, a
  competitor for sites on the host root)
• Gallex control solution for treating wound
  after removal of galled tissue.

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Bunch Rot
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Bunch Rot

• Caused by Botrytis cinerea various fungi
  bacteria
• Control via opening up canopy for air
  circulation

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Bunch Rot Early Stages
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Grapevine Leaf Roll Virus
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Grapevine Leafroll Virus

• Caused by a virus (GLRV)
• Transmitted by grape mealybug
• Symptoms are premature purpling and rolling of
  foliage in Cabernet franc
• No cure once infected

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Grapevine Leafroll Virus
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