Disease Risk of Potting Media Infested with Phytophthora ramorum Under Nursery Conditions.

Phytophthora ramorum has been found in potting media of containerized plants; however, the role of infested media on disease development under nursery conditions is unknown. This study assesses pathogen survival, sporulation, and infectivity to rhododendron plants in nursery pots with infected leaf litter that were maintained under greenhouse and field conditions. The influence of environmental conditions and irrigation method on disease incidence was also assessed.

Disease on Nursery Stock as Affected by Environmental Factors and Seasonal Inoculum Levels of Phytophthora ramorum in Stream Water Used for Irrigation.

A pear bait monitoring system was used to detect and quantify Phytophthora ramorum propagules in streams that flow through woodland areas with sudden oak death in Santa Cruz County, CA from 2001 to 2007. Stream propagules were detected most frequently or occurred in highest concentrations in winter and spring. The stream propagule concentration was characterized with statistical models using temperature and rainfall variables from 2004 to 2007.

Phytophthora Leaf Spot and Foliar Blight of Pieris japonica Caused by Phytophthora citricola in California.

During 2004, containerized nursery stock of lily-of-the-valley-bush (Pieris japonica 'Flamingo', family Ericaceae) in Santa Cruz County was affected by a foliar disease. Symptoms consisted of large leaf spots, many developing at the leaf tips that ranged in size from 1 to greater than 4 cm in diameter. Spots were dark brown to almost black, generally oval to round, visible from both sides of the leaf, and did not exhibit signs of any pathogen.

Downy Mildew Caused by Peronospora radii on Marguerite Daisy (Argyranthemum frutescens) in California.

In California, marguerite daisy (Argyranthemum frutescens [= Chyrsanthemum frutescens]) is an important, commercially grown, perennial flowering plant that is used as a potted plant, cutflower, and landscape plant. For two seasons (2003 and 2004), a downy mildew disease has been affecting marguerite daisy at wholesale container and field cutflower nurseries and retail nurseries in coastal California (Monterey, Santa Cruz, and San Mateo counties). The disease occurred early in the season (January) and continued to infect new foliage throughout the year whenever cool, foggy weather occurred.

First Report of Downy Mildew on Delphinium Caused by Peronospora ficariae in California.

Along California's central coast, delphinium (Delphinium species and cultivars) is grown as a cut flower and potted plant. In the spring of 2003, severe downy mildew was observed on various delphinium crops in Santa Cruz County. The disease was detected on cut flower Delphinium 'Volkerfrieden' in a greenhouse and adjacent field production areas.

First Report of a Leaf Spot Disease of Bells-of-Ireland (Moluccella laevis) Caused by Cercospora apii in California.

Bells-of-Ireland (Moluccella laevis) (Lamiaceae) is an annual plant that is field planted in coastal California (Santa Cruz County) for commercial cutflower production. In 2001, a new leaf spot disease was found in these commercially grown cutflowers. The disease was most serious in the winter-grown crops in 2001 and 2002, with a few plantings having as much as 100% disease incidence.

First Occurrence of Downy Mildew on Digitalis purpurea (Common Foxglove), Caused by Peronospora digitalidis, in California and the United States.

In California, Digitalis purpurea (common foxglove) and D. grandiflora (yellow foxglove) are grown as cutflower, potted, and landscape plant commodities. In the spring of 2002, after seasonably wet and cool weather, severe downy mildew was observed on potted common foxglove plants in commercial nurseries in coastal California (Santa Cruz County).

A Blight Disease of Dill in California Caused by Itersonilia perplexans.

In 2000, a foliar disease was observed in commercial field plantings of dill (Anethum graveolens) in coastal California. Initial symptoms consisted of a gray-green discoloration and wilting of the tips of dill leaves. As disease developed, many of the leaves discolored and collapsed, which gave the foliage a blighted appearance and made the leaves unsuitable for harvest.

Outbreak of Leaf Spot of Saponaria Caused by Alternaria saponariae in California.

Saponaria (Saponaria vaccaria [= Vaccaria hispanica]) is a Caryophyllaceae plant that is grown commercially in California as a cut flower. In 1998, a leaf spot disease devastated the commercially grown saponaria in coastal California. The entire saponaria crop was completely unmarketable because of extensive leaf spotting.

A New Root and Crown Rot Disease of Heath in California Caused by Cylindrocladium pauciramosum.

Heath (Erica capensis Salter) is a woody, evergreen plant used in Cali-fornia as a landscape shrub or ground cover. In 1997, a new root and crown disease was found in commercial nursery plantings of potted heath. A similar disease was found in 1998 on heath transplants being grown as liners.

Rust Disease of Oregano and Sweet Marjoram in California.

In 1996 and 1997, a rust disease was detected on commercial, fieldgrown oregano (Origanum vulgare) and sweet marjoram (Origanum majorana) in coastal California. Symptoms on both plants were similar and mostly consisted of small (2 to 5 mm in diameter), circular, brown, necrotic leaf spots that developed cinnamon brown pustules in the center of the spot or in concentric groups on the spot periphery. Pustules sometimes developed without spots.

First Occurrence of Downy Mildew of Statice, Caused by Peronospora statices, in California and the Rest of the United States.

In California, hybrid statice (Misty series; Limonium bellidifolium × Limonium latifolium) is grown as a commercial cutflower crop in fields and greenhouses. In 1997, downy mildew was observed on statice plantings in both southern (San Diego County) and central (Monterey and Santa Cruz counties) parts of coastal California. Initial symptoms consisted of light green, irregularly shaped leaf spots that, after a few days, became chlorotic.