Replanting after the removal of a host of Armillaria can be very difficult, as removal of all sources of inoculum is almost impossible unless it was a contained growing area, such as a pot, where all the soil can be removed. Therefore current advice suggests removal of the infected plant and if replanting in the area to use a less susceptible species.
However, the hosts of Armillaria tend to be trees and woody shrubs, often used as focal points, which are usually replanted with something similar. Therefore it is hoped that this work will enable us to better tailor the advice we can provide on this disease by understanding how any remaining inoculum may behave in the soil.
The factors currently being tested are the size of the piece of severed rhizomorph, the species of Armillaria, the growing media, and the length of time. These all relate to practical steps a gardener could take once their infected plant has been removed.
If the gardener was to rotovate the surrounding soil, after plant removal, would this help by reducing the size of the remaining rhizomorphs? To answer this question we are using two lengths of rhizomorph.
The species, once identified, may make a large difference to the advice given as the rhizomorphs of species such as A. gallica, behave in a very different way to those of other species, such as A. mellea.
Previous work suggests the rhizomorphs of A. mellea are short-lived, and often not used for infection; whereas those of A. gallica are seen to be produced much more frequently, and further from the original food source, as these are one of the main infection structures for this species. These differences would greatly affect the treatment of a site after infected plant removal.
The differing experimental growing media would help us understand whether soil enrichment, once the host plant was removed, could help suppress the rhizomorph growth. For this reason a loam is being used to model a quite ordinary soil, and then for comparison a compost derived from municipal waste collections, as this will hopefully model the compost made and used by gardeners.
Time is obviously an important factor. If the rhizomorphs are severed from their food source but can remain viable indefinitely in the soil, it would be important to never replant that area with a susceptible species, however if after time they ceased to be viable it would allow a gardener to replant with their choice. The rhizomorphs in this experiment are assessed on a regular basis to check for growth and viability.