Diagnostic Troubleshooting

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Diagnostic Troubleshooting

• Walt Stevenson
• Dan Heider
• Karen Delahaut

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Possible Causes of Crop Problems
Insects
Diseases
Weather
Crop Problems
Compaction
Nutrient Availability
Weeds
Pesticide Applications
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Gather a Complete History

• Know your plants.
• Know your key pests.
• What were the recent weather conditions?
• What cultural practices have been done?
• What were the previous crops in that location?
• What plant species are affected?
• What is the variety?
• Did the symptoms appear suddenly or gradually?
• Are their nearby sources of air pollution?
• Power plants, foundries, open burning sites,
  paper mills?
• How are the affected plants arranged in the
  field?
• What part of the plant is affected?
• Examine for both internal and external
• Examine roots as well as aerial plant parts
• SPECIFICALLY, what are the symptoms?

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Diagnostic Tools

• Handlens
• Shovel/trowel
• Knife
• Water
• Bags/vials, etc. for collecting samples
• Cooler
• Sticky traps
• Select references
• Information collection form ( a pencil)
• Camera digital if possible

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Lab Tests May Be Necessary

• Microscopic examination.
• Isolation of suspected pathogens on lab media.
• Electron microscopic examination.
• Serological examination for virus identification.
• Root soil examination for nematodes.
• Soil tests for pH, fertility, salt.
• Tissue analysis for micronutrient levels.
• Pesticide residue analysis.

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Diagnostic Look-alikes in Vegetable Crops
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Bacterial Brown Spot or European Corn Borer?
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Bacterial Brown Spot
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European Corn Borer
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Wilted Plants Cabbage Maggot? Herbicide
Damage?Excess Water? Clubroot?
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Wilted Cabbage Close-up
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Cabbage Maggot
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Clubroot
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Herbicide-Contaminated Transplant Water
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Bacterial Wilt or Squash Vine Borer?
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How to tell the difference

• What is the crop?
• Check for frass.
• Slit the stem look for bacterial exudate.

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Virus Infection or Herbicide Injury?

• Leaves are distorted, chlorotic, curled downward

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Pod Malformation
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Phenoxy Herbicide Injury (2,4-D)

• Which way are the leaves curling?
• What is the leaf color?
• Is there any leaf distortion?
• Other symptoms.

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Stunted Sweetcorn Herbicide, Rootworm,
Compaction, Root Rot?
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Herbicide Injury
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Corn Rootworm Damage
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Wilted Plants Verticillium?Fusarium? Juglone
Toxicity?Herbicide?
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Vascular Wilts
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Root Knot Nematode, Soil Compaction, Pythium,
orPoor Soil Drainage?
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Excess Water, Looper Damage, Black Rot,
Cultivator Blight, Severe Hail Damage?
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Black Rot
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Cabbage Lep Damage
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Herbicide Carryover,Seed Corn Maggot Damage or
Seedling Disease?
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Poor Drainage? Nematodes? Root Rot?Herbicide?
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Common Root Rot
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Herbicide Injury orAster Yellows
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Leaf Blight, Frost, Excess Water or Herbicide
Damage?
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Cercospora Leaf Blight