2018 ASHS Annual Conference

In 2015 and 2016, plants of almost 300 garden rose entries were field planted in Overton, Texas for evaluation of disease development and landscape characteristics. The entries included species and modern roses including hybrid tea, hybrid rugosa, and traditional and modern shrub type roses. Plants were planted in a randomized complete block design and evaluated monthly during the 2017 growing season for disease incidence of black spot (Diplocarpon rosae) and landscape performance. During the growing season at Overton, overall black spot incidence varied from 4.1 in June and July to 5.1 in November using a rating scale of 0 to 9 with 0 representing a total lack of disease and 9 denoting all foliage infected with heavy defoliation and reduced plant vigor. Many species roses such as Rosa bracteata and hybrids such as John Davis and Oso Happy Candy Oh exhibited the lowest black spot ratings. Highest ratings were given to mainly commercial cultivars such as Intrigue and Linda Campbell. Also, in 2017 a breeding population was planted to evaluate disease incidence. Rust was seen for the first time in the Overton plantings in this population and was only present in the R. setigera crosses. Forty percent of the seedlings of R. setigera x Bayse’s Thornless, 20% of the seedlings of R. setigera (or R. s. serena) x Pink Gnome, and a seedling of R. setigera x X566-81 were rust free. All crosses involving Driveway Red with R. setigera or R. s. serena were rust free. This information will be valuable for genetic studies and for determining entries useful for future breeding.