"Coleus (Solenostemon scutellarioides) and impatiens (Impatiens walleriana) are popular annuals used extensively in shaded landscape beds in the U.S. Coleus plants exhibiting disease symptoms were observed in New York and Louisiana in 2005 and throughout the country by 2006. This pathogen is an unclassified Peronospora species. Downy mildew (DM) on impatiens, caused by the oomycete Plasmopara obducens, rapidly defoliates impatiens and epidemics have been observed throughout the U.S. Epidemiological studies on both pathogens were conducted to determine the optimal environmental conditions for infection and sporangial production and release in the greenhouse atmosphere. A volumetric spore sampler was used in a greenhouse containing DM-infected coleus for two extended periods of time and environmental parameters recorded. A rapid reduction in recorded relative humidity prompted the release of high concentration of sporangia into the atmosphere. P. obducens sporulation was observed on inoculated impatiens when incubated at 20°C and 25°C while no pathogen sporulation was observed at 30°C. A leaf wetness period of 22656 hours yielded a greater proportion of inoculated leaves developing P. obducens sporangia than a reduced leaf wetness period of 3 hours. Twenty-one coleus cultivars were screened for DM susceptibility. None of the tested cultivars showed complete disease resistance. Reduced-risk fungicides were tested for efficacy against DM in coleus and impatiens. Defining the environmental conditions that favor DM sporulation, and identifying cultivars that are less susceptible to DM along with reduced-risk fungicides with proven efficacy provide an integrated management program."--Page ii.
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