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Eleven rose cultivars were field planted and evaluated weekly for disease, defoliation, and overall vigor in order to compare natural resistance to blackspot (Diplocarpon rosae). Alternative treatments were also compared for efficacy in low-maintenance disease control. Treatments included a bimonthly application of chlorothalonil, a bimonthly application of a horticultural oil, an application of chlorothalonil based on rain events, and a no-treatment control. Cultivars showed significant differences in disease severity, defoliation, and overall performance, with old garden rose varieties showing more natural disease resistance than modern susceptible varieties included in the study. Chlorothalonil applied on a 14-day spray schedule did provide a significant decrease in blackspot disease severity when compared to other treatments. A significant incidence of secondary disease including Cercospora rosicola and Botrytis cinerea occurred on old garden rose varieties. No treatment differences were found for these diseases. `Belinda's Dream', `The Fairy', and `Red Mediland' ranked highest in overall performance throughout the season.
Five antitranspirant materials, a horticultural oil, the fungicide chlorothalonil, and an untreated control were applied to rose plots using one of four application schedules. After 12 weeks, treatments were evaluated for their effectiveness in control of blackspot. Disease (P=0.0022) and defoliation (P=0.0008) showed significant treatment differences, while vigor and flowering were unchanged. Two antitranspirants, Stressguard 0.05% applied every 2 weeks and NuFilm17 1% alternated with chlorothalonil around rain events, gave similar disease control to weekly chlorothalonil applications. One antitranspirant, Vapor Gard, 1 % alternated with chlorothalonil around rain events, gave similar defoliation control to weekly chlorothalonil applications. These results indicate that blackspot disease can be effectively managed with fewer applications of chlorothalonil.
The root rot fungus Phytophthora parasitica is known to be very destructive to annual vinca (Catharanthus roseus). Phytophthora produces motile zoospores which swim freely in water, posing a special threat to crops grown using a recirculating water supply. Vinca were transplanted into 7 cm square pots containing a sphagnum peat:perlite medium. The medium was inoculated with the pathogen and plants were then placed in one row on each ebb and flow bench. Untreated vinca were placed in six additional rows on the benches. Separate benches were used to space plants at a distance of either 1 cm or 4 cm between pots. Plants were harvested biweekly over a six week period and tested for presence of Phytophthora. Cumulative results of root sampling revealed pathogen movement to 60% of untreated plants spaced at 1 cm, and to 30% of those spaced at 4 cm. Severe root injury (injury to root system ≥ 25%) was exhibited in 36% of the closer spaced plants, compared to 13% of those spaced at 4 cm. Phytophthora zoospores were detected in one tank which was used to irrigate plants spaced at 1 cm. Closer plant spacing enhanced the pathogen's ability to infect healthy plants.