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Entomology and Plant Pathology, Oklahoma State University 127 Noble Research Center, Stillwater, OK74078 405.744.5527 Vol. 12, No. 7 http://entoplp.okstate.edu/Pddl/ Apr 2, 2013 Plant Disease Corner, April: Fire blight, Pine tree blights, and Leaf spots Jen Olson, Plant Disease Diagnostician Cold weather has slowed the arrival of spring, but bud swell and flower bloom has finally arrived for many trees and shrubs. Spring diseases such as blight, leaf spot and anthracnose are common in years where spring is cool and wet. Often, heavy dews will provide enough moisture for these diseases to “bloom”. Trees and shrubs throughout Oklahoma have been under significant stress due to weather and stress predisposes plants to disease problems. Be on the lookout for the following diseases. Fire blight Fire blight is a common disease in Oklahoma and is caused by the bacterium Erwinia amylovora. Many members of the rose family are hosts of this disease, most commonly apple, pear, crabapple, catoneaster, quince and hawthorn. Susceptibility is highly variable and some trees and shrubs are resistant. However, even resistant trees can show symptoms of fire blight in cool, wet years. Symptoms appear shortly after bloom when a brown to black discoloration develops on flowers, leaves and twigs. The infection usually begins with the flower and spreads down the branch. Occasionally, leaves can be infected directly through the stomata (pores in the leaves) or wounds. The disease advances to the twig and the tip of the shoot may droop and produce a “shepherd’s crook” (Fig 1). Leaves, flowers and branches often take on a brown to black color which gives the disease the common name fire blight. Symptoms of the fire blight can be similar to those caused by chemical injury and frost damage. Laboratory tests can determine if the cause of shoot tip dieback is due to the bacterial pathogen. Clients should submit symptomatic shoots for testing.Black to brown cankers can form at the base of blighted shoots (Fig 2). Reddish-brown discoloration may be visible in the
|Okla State Agency||
Oklahoma State University
|Okla Agency Code||
|Title||Pest e-alerts, 04/02/2013, v.12 no.7|
Oklahoma State University. Department of Entomology and Plant Pathology.
Oklahoma State University. Cooperative Extension Service.
|Purpose||Plant Disease Corner, April: Fire blight, Pine tree blights, and Leaf spots, Jen Olsen;|
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|Digital Format||PDF, Adobe Reader required|
|ODL electronic copy||Downloaded from agency website: http://entoplp.okstate.edu/pddl/2013/PA12-7.pdf|
|Rights and Permissions||This Oklahoma state government publication is provided for educational purposes under U.S. copyright law. Other usage requires permission of copyright holders.|