During the past month I’ve noticed a problem with the ‘red apple’ groundcover in my landscape. The leaves of the plants have developed purplish and brown spots and the plants seem to be dying. Do you have any idea what this could be and what I should do to manage it?
We have found a new species of downy mildew in San Diego County that is attacking red apple groundcover (Aptenia cordifolia). The disease is a downy mildew, Peronospora mesembryanthemi. It has a pest rating of Q from the California Department of Food and Agriculture, which means it is a pest of quarantine significance (for now). No action will be taken against it on private property, but plants infected with this organism may not be sold in nurseries. It was previously reported in South Africa and New Zealand, but this is the first report of it in the western hemisphere.

There are currently no known chemical controls that will assist with managing this problem. Because it is possible that this disease is more likely found in plantings that are in the shade, non-chemical options to help manage this pest include letting the area dry out, avoiding overwatering of the plants, and placing future plantings in sunny areas. If you suspect that you have this disease pest, we recommend that you bring a sample of the plant to the County of San Diego Department of Ag Weights and Measures to have it analyzed by our County Pathologist. Their address is 9325 Hazard Way, San Diego, CA 92123.