Strawberry Leaf Spot

strawberry-leaf-spotBiological information:

  • Common name: Strawberry Leaf Spot
  • Scientific name: Mycosphaerella fragariae
  • Family or class: Mycosphaerellaceae

Symtoms and/or signs to watch out for:

  • Leaf lesions 3-8mm in diameter
  • Dark purple/reddish in color

Life cycle:

  • Differs in southern/northern growing regions (warmer vs. colder)
  • Northern: 3 sources of primary inoculum: spores from overwintering sclerotia, and ascospores. Spores are produced in early summer and are spread mainly by water splash.

Mode of Reproduction:

  • Spore reproduction

Vectors for pest:

 

  • Carried through rain and moisture
  • Perfect conditions are at cool times of the day when plant is wet such as early mornings or after rainfall

 

 

Overwintering habit:

 

  • Sclerotia produced in winter on dead infected leaves

 

Alternate hosts:

 

  • Mycosphaerella fragariae is specific to the strawberry plant

 

Horticulture production information:

Preventative Strategies:

  • Plant in well-drained, preferably raised beds.
  • Limit overhead irrigation, drip irrigation is most desirable for prevention of fungal spread.
  • Use disease free plants when possible (although seedlings can have disease without showing signs until maturity). There are a number of Leaf Spot resistance varieties but none have shown total immunity.
  • Optimal fertility levels will also reduce fungal spread.

Threshold Levels:

  • Leaf Spot, as the name implies, generally targets the leaves of the strawberry plant. In severe cases, strawberries will form black (necrotic) seeds instead of the typical white seeds in the flesh. The threshold level for leaf damage is between 20-30%, at which point the disease begins to impede upon the photosynthetic rate of the plant.

Control Options:

Physical controls:

  • A common physical control option for strawberry cultivation is growing on straw beds or black plastic.
  • Straw beds reduce the rate of soil warmth in the spring and prolong soil temperature in the fall.
  • Black plastic reduces the spread of fungal spores residing in the soil. It also keeps moisture levels down which directly correlates with fungal spread.
  • Greenhouses, high tunnels, and or plastic row covers, will keep moisture off the leaves and fungal pressure down.

Historical notes from Farm to YoU NH:

 

  • Use of black plastic/straw
  • Drip irrigation used
  • Well drained, raised-beds

 

 

References:

http://www.fruit.cornell.edu/tfabp/strawleafspot.pdf

http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3015_08.pdf

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