Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Strawberry -- Leaf Scorch
 
Cause: Diplocarpon earlianum (asexual: Marssonia fragariae), a fungus that overwinters on old infected leaves. The disease is frequent in northern Idaho and western Oregon and Washington. Conidia are produced in acervuli and are splash dispersed to healthy tissue. Conidia are sticky and can directly penetrate the leaf cuticle. In spring rains, spores from just a few diseased plants can multiply and spread through the entire planting. Generally more severe in 2nd and 3rd year fields.
Symptoms: Small, dark purple spots develop on upper leaf surfaces and remain dark purple. A white center never forms, as with common leaf spot. Spots have an irregular outline. If numerous, spots run together, and leaves appear scorched. In severe cases, foliage is reduced considerably, and plants may be stunted. Infected fruit has elongated, slightly sunken, reddish areas or streaks, but the marks disappear as the fruit ripens.

Note the red blotches on the leaves and on the unripened fruit.

 
Cultural control:

  1. 'Hood' and 'Rainier' are resistant. 'Northwest', 'Puget Beauty', 'Shuksan', and 'Totem' have intermediate susceptibility. 'Benton', 'Linn', 'RedCreast' and 'Quinault' are susceptible.
  2. Space plants so foliage dries rapidly after rain and irrigation.
  3. Use optimal fertilization.
  4. Summer renovation will help reduce inoculum levels. In Oregon, it is recommended to renovate 2 to 4 weeks after the last harvest of June bearing types.
Chemical control:

  1. Syllit FL at 2.4 to 3 pt/A. Do not apply within 14 days of harvest. 48-hr reentry.
  2. Topsin 4.5 FL at 15 to 20 fl oz/A plus another fungicide. Do not apply within 1 day of harvest. 12-hr reentry.
Notes: When used for Botrytis control, iprodione has activity on leaf scorch.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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