A downy mildew caused by the oomycetous fungus, Peronospora mesembryanthemi Verwoerd has recently been confirmed by the USDA -APHIS from a red apple ice plant sample collected in San Diego. Since its first finding in San Diego County last summer, the disease has spread to Orange, San Bernardino, and Ventura counties and is now found in the Goleta area in Santa Barbara County. Peronospora mesembryanthemi was first reported from South Africa (Verwoerd, 1924) and later in the United Kingdom (Francis and Waterhouse, 1988) and New Zealand (McKenzie and Dingley, 1996), but has never been reported in North America. The host range of P. mesembryanthemi is thought to be limited to ice plants and it is currently found infecting the red apple ice plant, Aptenia cordifolia and the trailing ice plant or the pink carpet,Delosperma (syn. Mesembryanthemum) cooperi in California. Both these ice plant species are native to southern Africa. Because of their environmental hardiness, ease of growing, and bright, colorful flowers, ice plants are grown as ornamental plants or found as groundcovers. However, the red apple ice plant is listed as an invasive plant by the California Exotic Pest Plant Council. It can sometimes grow like a weed.
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