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Diseases of the Pyracantha

By Lori Norris ; Updated September 21, 2017

Pyracantha (Pyracantha spp.), also called firethorn, is hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9. They are evergreen shrubs with glossy green leaves and masses of yellow, orange or red berries. They have sharp thorns, and are often planted as a deterrent along fences or around windows. The flowers are small and white, and the fragrance is sometimes described as musky. The flowers attract bees and butterflies, and the fruit attracts birds. Pyracanthas may suffer from a number of diseases, but there are resistant cultivars on the market, so research purchases carefully.

Scab Disease

Scab, a common disease of pyracanthas, is caused by fungus Fusicladium pyracanthae, and the disease affects both berries and fruits. It first appears on foliage, showing up as small greenish-yellow spotting. As the disease progresses, these spots will turn black. The berries will then exhibit the same black, scabby spots. The disease tends to be more severe when the environment is moist and the temperatures are mild. Scab overwinters on the previous year's foliage, so early fungicide applications may prevent the disease from reaching new foliage.

Canker and Dieback

Fireblight, caused by the bacteria Erwinia amylovora, is a common disease of pyracanthas. Symptoms include wilted blossoms that eventually turn black, then cankers on the twigs which causes dieback. The cankers harbor the bacteria, which oozes from the lesion and is carried by wind, insects or rain to the healthy foliage. The fungus Botryosphaeria causes similar symptoms. Leaves wilt and die, branches develop cankers, and the wood under the cankers is discolored. Both diseases can be controlled by cutting out infected sections well below the infected area, but Botryosphaeria may be prevented with fungicide applications.

Root Diseases

Pyracanthas may suffer from at least a couple of fungal root diseases. Phytophthora symptoms include tip burn on the ends of branches, then branch dieback and possible death of the plant. This disease often occurs where soils are frequently wet or waterlogged. Verticillium wilt is caused by one of many verticillium fungi that exist in soils. Symptoms include wilting of small branches, yellowing foliage, stunted growth and defoliation. Just one or two branches may be affected, or the whole plant may be involved. Fungicides may be used in soils but often aren't effective.

Other Diseases

There are a couple of conditions in which pyracanthas exhibit disease-like symptoms, but the shrub isn't actually diseased. Cankers on trunks, for example, are often caused by diseases, but may also be caused by winter injury and it's difficult to tell the difference. The wound leaves an opening for disease, however. Sooty mold is caused by one of the Capnodium or similar fungi, and symptoms include a black, soot-like substance on leaf surfaces. However, the mold does not infect the plant, it infests the honeydew left behind by sucking insects. It affects the plant by inhibiting photosynthesis.

 

About the Author

 

Lori Norris has been writing professionally since 1998, specializing in horticulture. She has written articles for the Oregon Landscape Contractors Association, chapters of the certification manual for the Oregon Association of Nurseries and translated master gardener materials into Spanish. Norris holds a Bachelor of Arts from Linfield College.