Categorization of garden roses for field growth response to black spot disease

Abstract

Five garden rose cultivars and an accession of Rosa roxburghii were field planted at Overton in randomized complete blocks of 5 plants per plot to determine plant growth responses to black spot disease. Half of the plots were protected with fungicide applications and compared to the plots that were not sprayed. After two seasons of treatment, disease ratings confirmed that the fungicide applications fully controlled the disease. Disease ratings for unprotected plants corresponded to a reduction in growth in relation to the protected plots as measured by final height and dry weight. The cultivars ‘Sun Flare’ and ‘Peace’ were the most affected and had the only mortality in the study with a loss of 100 and 55% of the unsprayed plants, respectively. The cultivars ‘Red Radiance’, ‘Carefree Wonder’, and ‘Old Blush’ exhibited moderate reductions in growth due to lack of fungicide protection. There was no difference in growth between sprayed and unsprayed plots of Rosa roxburghii corresponding to a lack of disease on unprotected plants. The plant responses in this study show the range of response of garden rose types to black spot infection in northeast Texas.