Armillaria Root Rot

In a yard and home landscape situation your control alternatives are very limited. In commercial situations several fumigant materials can be used to suppress Armillaria mellea infected sites. However, none of these materials are registered for use in residential landscape situations. Therefore, the alternatives for managing Armillaria root rot are to change the landscape planting to immune and resistant species and to alter the management of the landscape to put the Armillaria at a disadvantage. The cultural management of the landscape is important. I recently talked with an Armillaria expert from UC Davis, and he informed me that even so-called immune/resistant plants can succumb to Armillaria if they are grown under high moisture conditions during the summer and fall growing season.

Armillaria mellea has a wide host range including many woody and herbaceous plants. Therefore, if you have a landscape planting in which a variety of shrubs and trees are dying, you should suspect Armillaria mellea as a possible cause. Fortunately, the fungus is soilborne and generally moves (the margins of the infected site) very slowly creating an ever larger infected zone.

To stop or at least dramatically slow the progress of Armillaria, the landscape should be converted to a Mediterranean type, i.e., winter/spring wet (rain or irrigation) and summer/fall dry (little or no irrigation). A Mediterranean garden should be planted in the fall so the plants can become established during the winter and spring before the water is turned off. Turf grass and high water use plants will not be part of this landscape.