Rudy Haag Burning Bush [Euonymus Alatus] as a Non-Invasive Alternative to Current Burning Bush Cultivars

Burning bush (Euonymus alatus) is a popular ornamental shrub and an easily grown, profitable nursery crop.  Many states, however, have designated burning bush as an invasive plant.  Rudy Haag burning bush (E. alatus ‘Rudy Haag’) is a nearly seedless cultivar that may have a significant marketing advantage for nursery producers if data to support a non-invasive character can be substantiated. Fruit display is often promoted as a desirable characteristic in landscape ornamentals, but prolific seed production is often cited as an indicator of invasive potential.  Preliminary observation indicated that cultivars of burning bush differ in fecundity under natural pollination conditions.  The objective of this project was to document the potential risk of ‘Rudy Haag’ burning bush as an invasive plant species based on seed production.  E. alatus ‘Compactus’ and ‘Rudy Haag’ plants of a flowering size were established in field plots at two locations, Lexington and Princeton, KY.  In Kentucky, both cultivars of burning bush flowers as plants are leafing out in late April through May.  Seeds mature by late fall and usually develop as a single ovule encased within a brightly colored aril inside a dry capsule.  Under full sun conditions, ‘Compactus’ and ‘Rudy Haag’ produced an average of 1238 and 12 seed per plant, respectively, across three years and two production sites.  In Lexington, a 75% shade treatment was also included, but had no effect on seed production.  ‘Compactus’ averaged 1514, 1061 and 240 seed per plant in 2005, 2006 and 2007; significantly fewer seed were produced in the last harvest year.  ‘Rudy Haag’ plants produced no seeds the first year and an average of less than six in the subsequent two harvest years.  Field and greenhouse pollination combinations (self-, intra- and cross-pollinated) between ‘Compactus’ and ‘Rudy Haag’ were unsuccessful with no subsequent seed development.  In a simulated understory seed bank study using E. alatus ‘Compactus’, no germination occurred in the field or under germination conditions following exhumation as compared to bush honeysuckle (Lonicera), which germinated readily under both conditions.  Burning bush seed had limited persistence in the soil with an estimated viability of 38, 29, 9 and 2% after 3, 6, 9 and 12 months in soil, respectively.  Minimal germination and limited persistence as well as extremely low seed production under natural and supplemented pollination conditions support a low invasive risk of using E. alatus ‘Rudy Haag’ in landscape plantings.