Disease of the Month - Anthracnose of Strawberry

 
  Hort Snacks - August 2017
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 Causal agents: Colletotrichum fragariae; C. acutatum; C. gloeosporioides

Crops Affected: strawberry

Disease Cycle:

  • Different species can cause different diseases
    • Crown rot
    • Fruit rot
    • Leaf spots
  • Affects foliage, runners, crowns and fruit
  • Typically introduced in infected plants
  • Can overwinter for a short time (up to 1 year) on debris
  • Spores are produced in warm, humid weather
    • Spread by rain splash or irrigation
    • Spores may also be transferred by clothing and equipment
  • Wetness is required for infection
SYMPTOM
C. acutatum
C. fragariae
C. gloeosporioides
Crown rot
X
Fruit rot
X
X
X
Black leaf spot
X
X
Irregular leaf spot
X
Information courtesy www.fruit.cornell.edu

Symptoms
  • Occur on green or ripe fruit
  • Brown or black, sunken lesions
    • Tend to be small (typically less than 1.5cm across)
  • In humid conditions
  • Salmon (pink-orangey) coloured ooze (filled with spores) is released from lesions
  • Dark, sunken lesions form on petioles, runners and crowns
  • Daughter plants may die
  • Outer leaves may die prematurely
  • Plants may collapse from crown rot
  • Crowns may exhibit a reddish-brown streaking when cut lengthwise
    • Looks a bit marbled
  • Dried up, dead flowers or small, hard dried up fruit may be observed if infections occur during flowering
Anthracnose lesion on fruit
Sunken elliptical Anthracnose lesion on runner
Anthracnose lesion on leaf petiole
Photos by OMAFRA.gov.on.ca
Symptoms of Anthracnose crown rot (possibly Phytophthora – difficult to tell)
Photo by OMAFRA.gov.on.ca /
Photo by Frank Louws, North Carolina State University

.
Telling the difference between Anthracnose & look-a-likes
Look-a-like Disease
Symptoms
Botrytis Grey Mold
  • Fruit lesions often associated with the calyx
  • Lesions develop grey fuzzy mould and grey spores
Leather Rot
  • Indistinct lesions
  • Smell foul
  • Spores that develop are white
Verticillium Wilt
  • Wilted plants, but crowns do not have the reddish discolouration
Phytophthora Crown Rot
  • Plants wilt
  • Crowns have reddish discolouration

Conditions Favouring Development:
  • Very weather dependent
  • Splashed rain
  • Warm, humid conditions
    • 20-32°C and 100% RH
Management:
  • Start with clean plant material
    • Some varieties have resistance (most don’t)
  • Practice good sanitation
    • Remove infected fruit from the field
    • Clean up crop debris between crops
    • Clean equipment between fields
  • Maintain a good rotation between non-host crops
  • Control weeds
    • Some weeds may be hosts
  • Work in infected fields last
  • Clean clothing and equipment after working in infected fields
    • Spores can survive on clothing for several weeks
  • Avoid over fertilizing plants, specifically Nitrogen
    • Vigorous plants are more susceptible
  • Ensure a good layer of straw is in place
    • Straw reduces rain splash and disease spread
  • Use drip irrigation instead of sprinklers
  • Apply registered fungicides, where appropriate
 
 
 
 
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on July 28, 2017.