Sudden oak death: Nursery survey update

To date, Minnesota is the only state that has implemented a survey of potential nursery pathways for the introduction of the fungus causing sudden oak death, Phytophthora ramorum. Again the commitment of the MN Dept of Agriculture to manage potentially damaging invasive plant pests shines through. For the Pest Alert, see USDA Pest Alert.

University of California at Davis and APHIS are providing voucher specimens, verification protocols and training. UMN and USFS S&PF staff are culturing the samples collected and will be running molecular tests to verify the pure cultures they obtain. To date, MDA staff have collected 142 rhododendron samples and 19 oak samples (from the surrounding woods) from 26 nurseries around the state. These samples are being cultured now, so have not yet been identified. But to date none of the cultures have produced chlamydospores (P. ramorum is a prolific producer of chlamydospores, the resting spore stage of Phytophthora), suggesting that none of the cultures are the infamous ramorum.

On another note, a second Phytophthora species has shown up in a few of the oak samples taken in California. The fungus has yet to be identified, but closely resembles one found on holly.