My Large Butterfly Bush Is Dying

Identification

• Butterfly bush is susceptible to root rot disease or phymatotrichum root rot caused by Phymatotrichum omnivorum. The soil borne pathogen is most prevalent in high alkaline or calcareous soils. The fungus remains in soils for extended periods in the form of small seeds known as sclerotia.

Damage

• The fungus commonly infects plants in soil temperatures of about 82 degrees Fahrenheit. Affected foliage starts to dry and brown but remains attached to the shrub. Plants die in patches of circular areas. The fungus decays the taproots. Infected roots develop a tan-color fuzzy growth or mold called mycelium. Wood reveals brown stains under the bark, and spore mats are visible on soil near the plants.

Control

• The best management strategy is to use resistant varieties and to avoid planting in areas with known prior cases of disease, according to the Oklahoma Cooperative Extension. The use of fungicides or soil solarization are not highly effective. Improve soils with organic matter, as this supports the growth of competing soil microorganisms.