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It's that time of year when landscapers and homeowners bring in oak leaves and leaves from other hardwoods such as maple and elm with scorched edges, to be tested for bacterial leaf scorch. Currently, there is a $20 charge per sample for bacterial leaf scorch (BLS) testing. For BLS testing, at least 20 leaves are required and the test may take up to two weeks to run. Check payable to University of Delaware.
Due to similarity of symptoms to other environmental and cultural disorders, a confirmation diagnosis is based on detection of bacteria in plant tissue. A laboratory test necessary to detect presence of causal bacteria relies on sampling approximately 15-20 petioles of leaves. Attached leaves provide the best specimens, for leaves collected in September. A positive detection of bacteria along with dieback indicates the tree in question will survive only a few years. Severely affected trees should be removed to reduce spread to nearby trees. The bacteria that cause BLS are not harmful to humans or animals.
Checks payable to University of Delaware, $20 per sample. Please indicate on the form that BLS testing is requested.  Delaware Cooperative Extension office staff may receive plant samples in the County Offices.
NFG August 2019

BLS has been very damaging to red oaks in Delaware and the Mid-Atlantic states since the early 1990’s

BACTERIAL LEAF SCORCH (BLS) of hardwood trees, shrubs, and herbaceous plants, is caused by the bacterium, Xylella fastidiosa, carried by small insects such as leaf hoppers and sharpshooters. BLS has been very damaging to red oaks in Delaware and the Mid-Atlantic states since the early 1990’s. Northern red oak and pin oaks under environmental stress are more susceptible. Symptoms include marginal discoloration or scorch of leaves in late summer or early fall, often with a yellow or dark band on the inside edge of the discolored area. Symptoms are similar to those caused by drought or root issues that interfere with flow of water and nutrients. Plants may not develop symptoms for a year or two after infection, but then thinning of branches occurs and trees die within 5 to 8 years.  Infection is confirmed with a lab test for a fee, so if confirmation is needed, please arrange to have samples tested by contacting the UDBLS Red Oak 2016 Plant Diagnostic Clinic. Please note that there is a $20 fee for BLS testing. To manage, maintain good tree vigor, and remove infected trees. A UD fact sheet has more info:
NFG 8/30/2016

A new fact sheet from UD Cooperative Extension highlights information on bacterial leaf scorch (BLS) of oak and other trees.  BLS has been problematic in oaks in the red oak group for almost ten years, and has led to the decline and death of many oaks in Delaware.