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Magnolias (Magnolia sp.) are economically important woody ornamental plants; however, plant damage associated with frost and powdery mildew (Microsphaera alni and Phyllactinia corylea) disease is a major production challenge. To understand the tree architecture and powdery mildew resistance, 26 yellow-flowering magnolias (Magnolia sp.) were evaluated in McMinnville, TN, USA (USDA Plant Hardiness Zone 6b). One-year-old containerized trees were planted in a field plot during Mar 2006, with 4.6-m plant-to-plant and 3.7-m row-to-row spacing. The experiment was a completely randomized block design with three single-plant replications. Plant height and canopy diameter were measured on Dec 2016 and Feb 2018, and the apical dominance ratio (i.e., indicating tree architecture) was calculated by dividing the height by the canopy diameter. Plants were evaluated for powdery mildew severity and defoliation using a scale of 0% to 100% of the total plant canopy affected or defoliated, respectively, from Aug to Oct of 2016 and 2017. The area under the disease progress curve (AUDPC) was calculated for the evaluation period of each year. The plant apical dominance ratio ranged from 1 to 3, with ‘Gold Cup’ and ‘Sun Spire’ having the highest value, and ‘Lois’, ‘Gold Star’, ‘Golden Gala’, ‘Solar Flair’, ‘Stellar Acclaim’, ‘Sun Ray’, ‘Sunburst’, and ‘Sundance’ having the lowest value (i.e., relatively round shape). Of the 26 cultivars, Sundance, Sun Spire, Sun Ray, and Gold Cup had the lowest powdery mildew severity (10% to 33% in 2016 and 40% to 60% in 2017), AUDPC, and defoliation. Cultivars Anilou, Gold Star, Golden Pond, Golden Rain, Golden Sun, Green Bee, Honey Liz, Judy Zuk, Koban Dori, Lois, Solar Flair, Stellar Acclaim, and Yellow Bird were highly susceptible to powdery mildew (>80% disease severity) and had the highest AUDPC values. Results of this research may aid breeders, nursery producers, and landscapers when selecting yellow-flowering magnolia cultivars with desirable tree architecture and resistance to powdery mildew.

Crapemyrtle (Lagerstroemia sp.) is a top-selling deciduous flowering tree in the United States, and its salability is often compromised by cercospora (Cercospora lythracearum Heald & F. A. Wolf) leaf spot. To compare cercospora leaf spot resistance, 32 crapemyrtle cultivars belonging to Lagerstroemia indica, Lagerstroemia fauriei, L. indica × L. fauriei, and L. indica × L. fauriei × Lagerstroemia limii and 12 cultivars or unnamed selections belonging to L. indica, L. indica × L. fauriei, L indica × L. fauriei × L. limii, L. limii, and Lagerstroemia subcostata were planted in field plots in 2004 and 2011, respectively. The experiment was a completely randomized block design with three and four replications in the 2004 and 2011 plantings, respectively. Plants were evaluated for cercospora leaf spot disease severity and defoliation using a scale of 0% to 100% foliage affected from August to October of 2015, 2016, and 2017. Area under the disease progress curve (AUDPC) was calculated for the evaluation period of each year. L. fauriei cultivars Fantasy, Kiowa, Townhouse, and Woodlander’s Chocolate Soldier and L. indica × L. fauriei Apalachee from the 2004 planting, and the L. subcostata and L. limii selections from the 2011 planting had lowest cercospora leaf spot disease severity ratings, AUDPC, and defoliation. L. indica × L. fauriei cultivars Choctaw, Miami, Natchez, Osage, Sarah’s Favorite, Tonto, Tuscarora, and Tuskegee, and L. indica × L. fauriei × L. limii Arapaho were moderately resistant to cercospora leaf spot, whereas cultivars belonging to L. indica and L. indica × L. fauriei × L. limii Cheyenne were highly susceptible to cercospora leaf spot. Results from this research may aid breeders, nursery producers, and landscapers in selecting crapemyrtle species and cultivars with cercospora leaf spot resistance.