The Q&A Archives: Kalmia latifolia Blight

Question: Could you help me determine the proper remedy to a dark brown blight that has infected my many acres of Kalmia (Mountain Laurel) located in Brookline, NH? Would a timely spray of dormant oil solve the problem? Is it more likely to be an insect pest or a disease or fungus? I would greatly appreciate any help you could give me.

Answer: Without seeing a sample of the damage, it's difficult to give you a positive identification and specific controls for the problem. Kalmia Latifolia is subject to leaf spot (Phyllosticta kalmicola) which produce irregular or circular, light gray spots with a purplish-brown border. The leaves may have black fruiting-bodies present and leaves fall prematurely. A good garden fungicide, sprayed when the buds open, will control this disease. The other problem Kalmia can have is blight (Diaporthe kalmiae). This disease is sometimes confused with winter injury. The spots are irregular, sometimes covering large parts of a leaf, especially along the margin. They are purple-brown and appear more or less zoned. The fungus may penetrate into the tip ends of the twigs and cause some blighting. In its advanced stage the fungus is called Phomopsis kalmiae. I'd suggest contacting the University of New Hampshire Cooperative Extension, 59 College Rd., Taylor Hall, Durham, NH 03824-3587, phone (603) 862-1520, and taking a specimen into their plant pathology lab for identification of the problem.

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