Elm Plantation Study
Plantation Establishment. In July 1995, the elm plantation was established at Holbrook Arizona, approximately 85 miles east of Flagstaff. The plantation is located at the Navajo County Fairgrounds in the center of Holbrook. This site was chosen because of high elm leaf beetle populations and abundant planting of Siberian elm which is highly susceptible to ELB. In 1998 we completed planting a second experimental plantation of 28 species and cultivars of elms within the 1995 planting.
Trees at the plantation are spaced 12 ft on center, mulched around the base, and irrigated using a drip irrigation system. Irrigation rates and other treatments are designed to simulate typical urban forest practices in this area.
Irrigation system being put in at Holbrook Plantation
The species and cultivars planted include the following elms (Ulmus sp.):
- Accolade (U. japonica x U. wilsoniana 'Accolade')
- Allee (U. parvifolia 'Allee')
- American (U. americana) - 3 cultivars
- Athena (U. parvifolia 'Athena')
- Camperdown (U. glabra 'Camperdownii')
- Charisma ([U. japonica x U. wilsoniana] x [U. japonica x U. pumila] 'Charisma')
- Corkbark (U. proquiqua) - 2 cultivars
- David (U. davidiana) - 2 cultivars
- Dropmore (U. pumila 'Dropmore')
- Dynasty (U. parvifolia 'Dynasty')
- Frontier (U. carpinifolia x U. glabra x U. pumila) - 2 cultivars
- Glory (U. parvifolia 'Glory')
- Green King (U. pumila x U. rubra 'Green King')
- Homestead ([U. hollandica x U. carpinifolia] x [U. pumila-ramosa x U. carpinifolia] 'Homestead')
- Japanese (U. japonica) - 3 cultivars
- Kings Choice (U. parvifolia 'Kings Choice')
- Large-fruited (U. macrocarpa)
- New Horizon (U. pumila x U. japonica 'New Horizon') - 2 cultivars
- Patriot (U. wilsoniana x [U. glabra x U. carpinifolia x U. pumila])
- Regal (U. carpinifolia x U. glabra x U. pumila) - 2 cultivars
- Sapporo Autumn Gold (U. pumila x U. japonica 'Sapporo') - 2 cultivars
- Siberian (U. pumila)
- Szechuan (U. szechuanica) - 2 cultivars
- Ulmus bergnanniana
- Ulmus chenmoui
- Ulmus parvifolia x Ulmus procera
- Wilson (U. wilsoniana) - 3 cultivars
Defoliation Estimates. Every year we assess susceptibility to elm leaf beetle using a typical insect defoliation estimate procedure. This procedure consists of comparing defoliation to photographic templates of elm leaves defoliated to known levels. Each tree is assessed by 2 estimators and the results averaged.
Sheri Mann and Paul Bosu assessing an elm for damage by the elm leaf beetle
Defoliation estimates from 1998 varied from 0 to 33%. In general, Siberian elms (U. pumila) were very susceptible, while Chinese (U. parvifolia), Japanese (U japonica), and Wilson elms (U. wilsoniana) were resistant. This pattern of susceptibility across species in 1998 was consistent with results from the previous 2 years.
Hybrids that include Siberian elm parentage tend to be susceptible to elm leaf beetle, while hybrids containing Chinese elm tend to be resistant to elm leaf beetle.
Environmental Tolerance. Every year we assess survival, growth form, leaf color, leaf scorch, and tip and branch dieback on a 1 to 5 scale (1 being the best) by two independent visual estimates. We followed the same methodology as described for defoliaiton estimates.
Survival. There were ten species that experienced greater than 50% mortality over the first year of the plantation:
- U. americana
- U. americana - UW
- U. parvifolia 'Athena'
- U. parvifolia 'Allee'
- U. macrocarpa
- U. wallichiana
- U. davidiana
- U. szechuanica
- U. glabra 'Camperdown'
- U. wilsoniana
Leaf Color. Ulmus carpinifolia x U. pumila 'Frontier' and U. parvifolia x U. propinqua had darker green foliage (rating < 2.0) as compared to the other elms which had lighter shades of green foliage (ratings > 2.5).
Leaf Scorch. Some degree of leaf scorch was observed on thirteen elm genotypes. 'Regal elm', 'Frontier', U. parvifolia x U. propinqua, and U. pumila 'Sapporo' had minimal leaf scorch (rating < 1.7). In contrast, 'New Horizon, 'Accolade', and 'Prospector' had nearly 50% of their canopies exhibiting some degree of leaf scorch (ratings = 2.5 to 2.7). Leaf scorch was higher in 1997 for all elm genotypes, in most cases approaching or exceeding 50%. In 1998, leaf scorch declined to 1996 levels.
Tip and Branch Dieback. Extensive dieback was seen with the 'Homestead elm' which approached or exceeded 50% (ratings = 2.8 to 3.9). U. pumila and 'New Horizon' consistently showed at least 25 % dieback (rating > 2.0) of growing tips. Less than 25 % dieback (rating < 2.0) of branch tips was observed on the remaining elm genotypes.
We observed considerable variation in environmental tolerance across all twenty-three elm genotypes tested. Recent popular genotypes containing U. pumila, U. japonica, and U. wilsoniana including U. pumila 'Dropmore', 'New Horizon', 'Sapporo', 'Homestead', and 'Prospector' appear to be less tolerant to the local environmental conditions of east central Arizona. U. parvifolia x U. propinqua, 'Regal elm' and 'Frontier' showed the greatest tolerance to the environmental conditions of east central Arizona.
Summary Recomendations: As with any research project, it is important to not make recommendations too soon. Trees take a long time to grow and potential future problems may emerge with any of the elm cultivars mentioned above. Individuals who enjoy trying new things may want to try one or two of the new elm cultivars recognizing this limitation. With each additional year, we will be more confident with our recomendations.
Last Updated ( Thursday, 10 July 2008 )