Pacific Northwest 1998 An Online Guide to Plant Disease Control

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Pear -- Decline
 
Cause: Pear decline is caused by Candidatus Phytoplasma pyri that is transmitted by pear psylla. It also can be transmitted by grafting and budding. Decline is much more prevalent on trees with rootstocks of Pyrus ussuriensis or P. pyrifolia than on trees on domestic P. communis roots. The organisms kill phloem cells at the graft union of specific root-scion combinations, preventing the tree from transporting sugar from its top to its roots. Sugar accumulates above the graft union as stored starch while roots die from starvation. The reduced root system results in the slow decline of the tree.

Quick decline symptoms result from an additional stress acting directly on roots (usually Phytophthora or Pythium root rot). Leaves turn red early due to starch accumulation in the upper tree.

Symptoms: Pear decline is characterized by two phases: quick decline and slow decline. Trees may wilt, scorch, and die in a few weeks or lose vigor over several seasons during which foliage gets sparse with little or no terminal growth and leaf size is reduced.

An abnormal early red leaf coloration has been observed frequently on affected trees. Examining the graft union reveals a brown line on the cambial face of the phloem tissue. (Use a pocket knife to expose the cambium.)

Early or premature foliar discoloration is a general symptoms of this disease.

 
Cultural control:

  1. Use resistant or tolerant rootstocks.
  2. Use the best orchard management practices, including the best possible insect and disease control, irrigation, drainage, fertilization, and pruning.
  3. Control pear psylla.
  4. When grafting Asian pear trees over to European (P. communis) cultivars, graft below the union of the Asian pear with its rootstock to avoid creating a highly decline-susceptible tree.
References:
Fridland, P.R., ed. 1989. Virus and Viruslike Diseases of Pome Fruits and Simulating Noninfectious Disorders. Publication SP0003. Pullman, WA: Washington State Cooperative Extension.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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