See:
Rhododendron - Phytophthora Blight and Dieback
Cause The fungal-like organism Phytophthora sp. has been found in both the nursery and landscape. In one case an isolate of P. citricola was found in diseased nursery plants. Although identification to a specific species has rarely been done, none have been P. ramorum which can also infect Arctostaphylos spp. Records indicate that P. nemorsa and P. pseudosyringae have also been recovered but it is unclear where these plants were growing. Kinnikinnick was found to be very susceptible when inoculated with P. cactorum, P. cinnamomi, P. citricola, or P. citrophthora.
Plants in this family are low water users. Poorly drained, waterlogged soil or media favors these water-mold organisms. The organisms survive unfavorable periods as oospores or chlamydospores in plant debris. Low temperatures, wet conditions and wounds also favor above ground disease development.
Symptoms Nursery-grown plants have shown stem and root rots as well as leaf blighting and twig dieback. Landscape plants generally have branch diebacks. Foliar discoloration and leaf blighting may also occur.
Cultural control
- Purchase healthy appearing plants.
- Avoid over-watering especially when using automatic sprinkler systems that come on every day using the same amount of water.
- Provide good drainage for plants in beds, fields, or containers.
- Rake up and destroy dead leaves around the base of plants.
- Prune off infected leaves and branches.
- Avoid reusing pots from a previous crop for propagation. If pots must be reused then wash off all debris and soak in a sanitizing solution or treat with aerated steam for 30 min.
Chemical control No chemicals are specifically registered for this crop; however, there are many chemicals that could be used if not phytotoxic to plants.
- Although not specifically registered, according to IR-4 data, products such as Heritage are safe on this crop. These products may be of some benefit.
Reference Linderman, R.G., Davis, E.A., and Marlow, J.L. 2006. Response of selected nursery crop plants to inoculation with isolates of Phytophthora ramorum and other Phytophthora species. HortTechnology 16:216-224.