CORVALLIS, OR--Hazelnut production is an emerging industry in the United States. Although U.S. growers currently account for only 3% to 5% of the world's hazelnut production, the country is the world's largest producer of nuts for the in-shell market. In 2009, 78% of the U.S. hazelnut crop was sold as in-shell nuts. To cater to consumers, who prefer thinner shelled nuts because they are easier to crack, scientists have bred thinner-shelled hazelnut selections for the in-shell market. Although popular with consumers, the thinner-shell nuts can present challenges to growers, including increased susceptibility to pests and disease.
A major insect pest in hazelnut orchards in North America is the filbertworm, a moth that causes hazelnut growers substantial expense in terms of control costs (translating to approximately $2.2 million in 2006). The filbertworm is native to North America and in found in Oregon White Oak, wild hazelnuts, and Catalina cherries. In Oregon, where 99% of the U.S. hazelnuts are produced, filbertworm larvae infest hazelnuts throughout nut development and maturation from June through September.
Scientists from Oregon State University studied filbertworm susceptibility in 25 hazelnut tree cultivars located at the USDA National Clonal Germplasm Repository (USDA-NCGR) in Corvallis, Oregon. Researchers Ute Chambers, Vaughn Walton, and Shawn Mehlenbacher designed the extensive study. "The USDA-NCGR hazelnut collection provided the unique setting for our study with hazelnut trees grown under the same climatic and management conditions and exposed to pest pressure for multiple years," noted lead author Chambers. The trio published the report of their work in HortScience.
The researchers measured shell thickness of 17 of the cultivars at the thinnest and thickest points of the basal scar as well as at the side of the shell wall. They found that filbertworm infestation--which ranged from 2% to 89% per tree--and shell thickness varied significantly among the cultivars. The data showed that filbertworm infestation significantly increased with decreasing shell thickness at the basal scar, where filbertworm larvae typically penetrate the nut. Nut infestation was not correlated with the thickness of the side wall.
"Our data suggest that a thicker basal scar in hazelnut cultivars contributes to resistance against filbertworm infestation," Chambers noted. "How exactly thicker shells lead to lower infestation is not known. Thicker shells, specifically the basal scar area around the micropyle, are possibly more difficult and time-consuming for neonate filbertworm larvae to penetrate. Our data indicate that already small increases in thickness at the micropyle correlate with a decrease in the percentage of infested nuts."
Chambers, Walton, and Mehlenbacher concluded that growing filbertworm-resistant hazelnut cultivars with thicker shells may be beneficial to producers in terms of reduced pesticide use and environmental impact. "In the producer's interest, however, these benefits need to be carefully weighed against potential costs such as dislike by consumers, increased cost of cracking thick-shelled nuts, and less favorable kernel-to-shell ratios," they added.
The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/content/46/10/1377.abstract
Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at ashs.org