Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Calla Lily -- Soft Rot
See Also: Iris, Rhizomatous -- Bacterial Soft Rot
 
Cause: The bacteria Erwinia caratovora subs. carotovora enters plants though wounds. Wounds may be from physical injury to the rhizomes or from living organisms like insects or fungi. Soft rot may be the result of many other diseases such as those caused by Pythium. The disease is favored by moist conditions. Frost can also cause a melt down of the entire plant. The bacteria survive in old plant debris and infected rhizomes. They can be spread by transplanting, irrigation water or cutting and digging tools. This disease is considered the most important factor limiting production.
Symptoms: Plant parts become soft and slimy. Generally found at the base of leaves or anywhere on the rhizome. Leaves may appear water-soaked and are soft and slimy. Leaves start out turning dark green, may have spots then wilt, turn yellow and die. Typically, the foliage and flower stalks develop a brown, soft rot at the soil surface.

The rhizomes of this plant have soft rot.

 
Cultural control:
  1. When receiving rhizomes, unpack immediately and let dry out under mild dry conditions to let abrasions heal.
  2. Discard any diseased rhizomes immediately. Wash hands and equipment well before handling more plant material.
  3. If soaking in Gibberellic acid for increased flowering make sure soak times are short and rhizomes are dried quickly and thoroughly. Dip tanks should use fresh water and be cleaned frequently.
  4. Plant in well drained soil or soil-less media.
  5. Be sure to plant the rounded side down and the part where the roots and sprouts emerge at the top.
  6. Keep rooting media moist but not overly wet or dry. When irrigating, do not let water pool or splash. If an outbreak occurs stop irrigating right away and let plants dry out before removing.
  7. Do not apply excessive nitrogen.
  8. It has been reported that yellow and orange colored cultivars are susceptible while white and cream colored cultivars are not as susceptible.
Chemical control: Fungicide drenches (a mix of 2 or more) are recommended to prevent injury from soilborne fungal pathogens. Several bactericides are also used in the industry but few are legal. Antibiotics are not labeled for this use. Disinfectants may be used but have a very short if any residual effect.
  1. Phyton 27 at 3 oz/10 gal water. Soak bulbs for 5 min and allow to dry before planting. May not be very effective. 24-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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