Pacific Northwest 1998 An Online Guide to Plant Disease Control

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Iris, Rhizomatous (Iris germanica) -- Bacterial Soft Rot
 
Cause: The bacterium Erwinia carotovora subsp. carotovora attacks several hosts. The organism is in most cultivated soils and regularly overwinters in soil. Bacterial soft rot can attack plants any time of the year but often is noticed in the critical months before bloom. Seedlings sometimes suffer at the beginning of their second year, and so do established plants that have stayed too long in one place and become congested.
Symptoms: Yellowing or browning of leaves, especially the fan's outer leaves, is an early symptom, resulting from a soft decay of the leaf base or of the rhizome itself. Eventually, tops die. When infected plants are lifted for dividing, often empty shells are all that remain of the rhizomes. The organism enters through wounds.
Cultural control:

  1. Destroy all infected plants and rhizomes.
  2. Avoid wounding rhizomes when digging.
  3. Dry rhizomes in sun and replant in a new well-drained site.
  4. Plant shallowly to expose part of rhizome to the sun.
  5. Divide plants frequently enough to avoid serious congestion.
Chemical control: Combine with cultural control methods because chemical control is difficult and often ineffective.
  1. Phyton 27 at 1.5 to 2 oz/10 gal water. 24-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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