How to Manage Pests

UC Pest Management Guidelines

COMMENTS ON THE DISEASE

The phytoplasma organism that causes pear decline is carried by pear psylla. Psylla transmit the disease when they feed on pear foliage. The expression of the disease depends on rootstock susceptibility, tree vigor, and psylla numbers. The organism apparently does not multiply in pear trees as well as it does in pear psylla. Good pear psylla control usually results in disease remission even when rootstocks are highly susceptible.

DAMAGE

Poor shoot and spur growth, dieback of shoots, upper rolling of leaves, reduced leaf and fruit size, and premature leaf drop characterize pear decline. Sudden tree collapse can result from tissue damage at the graft union on highly susceptible rootstocks such as Pyrus serotina or P. ussuriensis, but slow decline of trees is more common. Trees on tolerant rootstocks may show mild to moderate symptoms that occasionally become severe if very high psylla populations occur in conjunction with other tree stresses.

MANAGEMENT

Commercial pear rootstocks currently available, with the exception of Pyrus calleryana, are essentially tolerant to pear decline and produce excellent crops in spite of recurring pear psylla populations and exposure to pear decline. Tolerant rootstocks include Bartlett seedling, Winter Nelis, Old Home X Farmingdale, and Pyrus betulaefolia. To keep the disease in remission on susceptible rootstocks, control pear psylla and maintain trees in good vigor, and reduce stress caused by inadequate irrigation, nutrient deficiency, weed competition, lack of pruning, and pest damage.

There is no known biological control of the pear decline phytoplasma organism. Indirectly, biological control of pear psylla can reduce disease expression.

PUBLICATION

UC IPM Pest Management Guidelines: Pear
UC ANR Publication 3455
Diseases
R. B. Elkins, UC Cooperative Extension Lake County
W. D. Gubler, Plant Pathology, UC Davis
L.G. Varela, UC IPM Program, UC Cooperative Extension Sonoma County

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