Management of Field Diseases

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Management of Field Diseases
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Use an Integrated Approach to Manage Diseases

• Pathogen
• Sanitation
• Fungicides
• Environment
• Air movement
• Moisture
• Host
• Resistance
• Injury
• Stress

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Soilborne Diseases

• Soreshin Damping-off
• Typical soilborne (monocyclic) disease
• One disease cycle per season.
• Disease cant be stopped once it starts
• Pathogen (Rhizoctonia solani) survives between
  crops on residue and organic matter.
• Most effective control is to reduce or limit
  buildup of pathogen in soil
• Rotation
• Destroy or turn under crop residues

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Black Shank

• Black shank has steadily spread throughout KY
  since it first appeared in 1934 (Todd Co.)
• Causes more losses on an annual basis than all
  other diseases combined
• Well-established not likely to disappear

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• Easily spread
• Persistent

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Black Shank Biology

• Soilborne disease
• Pathogen (Phytophthora nicotianae) is carried
  over in soil, roots, stalks, etc.
• Control should focus on
• Reduction of pathogen in soil (rotation)
• Limiting ability of pathogen to infect crop
• Resistant varieties
• Ridomil Gold or Ultra Flourish

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The Environment Black Shank

• Temperature
• Warm weather favors infection
• Moisture
• High moisture needed for germination of infective
  structures
• Saturated soils facilitate movement of swimming
  spores

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Management of Black Shank

• Combine tactics
• Cultural practices
• Resistant varieties
• set healthy plants
• Ridomil (preventive)

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Cultural Practices

• Rotation
• 3-5 years away from tobacco is a general
  recommendation
• gt 5 years out of tobacco might be needed where
  black shank is severe
• Grasses and related crops are best choices
• Sods, fescue
• Even 1 year out of tobacco can dramatically
  reduce black shank severity in a problem field

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Cultural Practices

• Sanitation keep black shank out of clean areas
• Clean equipment and feet when moving between
  fields
• Avoid using surface water (ponds, creeks, rivers)
  to set plants, or irrigate crops in the field
• Destroy tobacco stalks promptly and correctly
• Land preparation
• Improve drainage
• Dont over-fertilize
• Keep pH around 6 (especially during rotational
  period)

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Black Shank Resistant Varieties
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Resistant Varieties

• Moderate levels available
• Consult Guide to Burley Tobacco Varieties
• Disease pressure and rotation history should
  dictate the variety to be planted
• Plant a variety with highest level of resistance
  where risk is greatest
• Use in conjunction with other practices
• Rotation
• Ridomil Gold / Ultra Flourish
• Keep in mind that no variety is IMMUNE to black
  shank

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Resistance to Black Shank in Common Dark
Varieties
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Resistance to Black Shank in Common Burley
Varieties
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Managing Black Shank with Soil-Applied Fungicides

• Mefenoxam is the only effective active ingredient
  (a.i.) on the market at this time
• Ridomil Gold EC / SL (new) or Ultra Flourish
• Mefenoxam products can be used prior to planting,
  at 1st cultivation, and at layby (roughly 3 weeks
  between applications)
• Ridomil Gold 3 pt/A total
• Ultra Flourish 3 qt/A
• Ridomil products must be incorporated after
  application (mechanically or by irrigation /
  rain)
• Good soil moisture is critical to success
• Best used with good resistance

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Fusarium wilt

• Problematic in some areas
• Pathogen very persistent in soil
• Nematodes increase incidence losses

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Fusarium Wilt

• Cultural practices the most practical controls
• Long rotations or abandon site
• Resistant varieties
• Soil chemicals may not be practical for many
  growers
• Chloropicrin

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Black Root RotThielaviopsis basicola

• Caused serious losses in KY prior to the 1950s
• Disease began to drop in importance with the
  introduction of resistant varieties
• Favored by cool soil temperatures and soil pH gt
  6.5
• Cover crops can also increase severity
• Alfalfa other legumes
• Barley rye predispose roots to infection
• Poor rotation increases risk of disease

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Black Root Rot - Symptoms
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Black Root Rot - Management

• Rotation and sanitation
• Use good rotation (as for black shank)
• Deep-turn to bury debris
• Cover crops
• Avoid legumes, rye, barley
• Keep soil pH below 6.5
• Avoid planting in cool soils
• Resistant varieties

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Leaf Diseases
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Blue MoldPeronospora tabacina

• Severity varies by year less a problem in
  western KY
• Has caused serious losses (1979, 1996, 2003)
• Typically worse when it appears early

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Managing Blue Mold

• Think preventively
• Monitor crop and weather
• Cool humid / wet weather favor disease
• Begin fungicide program when blue mold risk is
  present
• 3rd week of June is the historical beginning of
  the highest risk period

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• Keep Informed
• Newspaper, radio, TV
• CES
• KY Tobacco Disease Info Page
• KY Blue Mold Alert Mailing List

www.uky.edu/Ag/kpn/kyblue/kyblue.htm
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Comparison of Blue Mold FungicidesJessamine
County, 2006 (Carl Waits Farm)
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Target Spot

• Target spot is a serious problem in areas around
  KY
• Can cause yield losses up to 50
• Favored by moderate temperatures and high
  humidity
• Low N fertility also contributes to
  susceptibility
• Can be introduced on transplants
• Can carry over in the field

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Target Spot - Management

• Rotation and sanitation
• Control target spot in the float bed
• Use good rotation
• Deep-turn to bury debris
• Site selection
• Pick areas with good air movement little shade
• Fungicides
• Dithane DF minimally effective
• Quadris 2.08SC - labeled in 2006 for target spot,
  frogeye, blue mold
• Rate range 6-12 fl oz/A 31 fl oz/A per season

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Variety Narrowleaf Madole LC
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untreated
Quadris 8 fl oz/A (3 apps)
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Quadris and Foliar Diseases

• Quadris is not a true systemic fungicide
• Local systemic (trans-laminar) not redistributed
  in plant extensively
• Good coverage is critical to success
• Timing
• Needs to be in place before row middles close
• Late application might be needed to protect after
  topping
• Quadris can be an important part of a spray
  program
• Multiple diseases target spot, frogeye, blue
  mold
• May cause flecking / dont mix with EC
  pesticides
• Resistance management no more than 2
  consecutive applications

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Quadris Injury
Burley
Weather fleck-like injury that usually shows up
around shoulders of leaf Much more common in
burley than in dark Can occur at the 8 oz/A rate.
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FrogeyeCercospora nicotianae

• Mature leaves are most susceptible
• Favored by moderate temperatures and high
  humidity
• Control practices similar to those for target
  spot
• Avoid excess N

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Brown SpotAlternaria alternata

• Lower leaves usually infected 1st
• Favored by moderate temperatures and high humidity

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Important Bacterial Diseases of Tobacco

• Hollow stalk / stalk rot
• Angular leaf spot
• Wildfire

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Bacterial black stalk/ Hollow stalk
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Wildfire / Angular Leaf SpotPseudomonas syringae
pv. tabaci

• Caused serious losses in KY prior to the 1950s
• Introduction of resistant varieties has reduced
  this disease to minor importance
• Particularly problematic in outdoor plant beds
• Favored by warm temperatures and wet weather
• Wounding can increase severity

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Wildfire / Angular Leaf Spot - Symptoms
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Wildfire / ALS - Management

• Rotation and sanitation
• Use good rotation
• Deep-turn to bury debris
• Dont perform field operations when foliage is
  wet
• Resistant varieties
• Chemical control
• Agricultural streptomycin (100-200 ppm)

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Important Viral Diseases of Burley

• Tobacco mosaic (TMV)
• Virus complex
• Potato virus Y (PVY)
• Tobacco etch (TEV)
• Tobacco vein mottling (TVMV)
• Tobacco ringspot (TRSV)
• Alfalfa mosaic (AMV)
• Tomato spotted wilt (TSWV)
  
  
  

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Tobacco Mosaic
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Potato Virus Y
- Transmitted by aphids in a non-persistent
manner - Weeds, tomato, pepper can be reservoirs
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Tobacco Etch
Early symptoms
Later symptoms
- Transmitted by aphids in a non-persistent
manner - Several solanaceous hosts
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Tobacco Vein Mottling
- Transmitted by aphids in a non-persistent
manner - Weeds (especially ground cherry) can be
reservoirs
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Tobacco Ringspot
- Transmitted by nematodes (possibly thrips
aphids)
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Alfalfa Mosaic
- Transmitted by aphids in a non-persistent
manner - Alfalfa, clover can harbor virus
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Diseases Caused by Viruses

• Potyviruses / virus complex
• Transmitted by aphids
• Resistant varieties are a must (see Variety Guide
  for 2007 / ID-160)
• Control weeds in and around tobacco field

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Tomato Spotted Wilt (TSWV)

• Transmitted by thrips in a persistent manner
• Causes heaviest damage on seedlings
• Virus can survive on many plant species
• No practical control methods are available

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Management of Viral Diseases

• Resistant varieties
• Resistance to TMV virus complex found in many
  varieties
• Weed control trap crops
• Insect control
• Results variable

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