Vinca Cultivar Trials in Guam

Vinca (Catharanthus roseus (L.) G. Don) is a frequently grown as a ground cover in Guam landscapes. Seeds of forty-nine vinca cultivars were germinated in flats under outdoor ambient conditions. Over half of the cultivars died before transplanting due to disease. Surviving cultivars were transplanted into five raised beds containing soil amended with compost. The soil surface was covered with plastic mulch which was subsequently covered with dry iron wood branchlets. Drip irrigation was installed under the plastic mulch. Flower diameter, petal length, petal width, leaf length, leaf width, plant height, and plant diameter were compared among the cultivars. Chlorophyll readings were also compared for leaves from the tops of plant and lower leaves. Vincas, in Guam, generally succumb to foliar diseases during months of heavy rainfall. Diseases commonly observed included Phytopthora and Corynespera. A combination of less rainfall and the application of Banrot appear to have reduced the incidence of foliar disease during this trial. The Banrot treatment extended the survival of some of the cultivars through September, 2009. Cultivars began to flower 45 days after germination. The first cultivars to flower were: ‘Pacifica Icy Pink', ‘Heatwave Orchid', ‘Heatwave White', and ‘Santa Fe'. The last surviving cultivar was ‘Heatwave Cherry'.