By Faith Campbell, Emeritus environmental advocate and tree-pest expert
As I said in my previous post, the greatest pest risk is associated with imports of whole plants. The U.S. allows few imports of plants in soil; instead, plants must be imported a bare-root stock, which facilitates visual inspection. Still, bare-root plants can also transport a variety of pests and diseases.
Manuel Colunga analyzed plant imports that enter the country by ship.1 These represented almost two-thirds of the total value of all living plants intended for planting — not as cut flower arrangements — imported into the U.S., other than those from Mexico and Canada. The import data are collated for a limited number of categories, including roses; rhododendrons and azaleas; and trees and shrubs bearing fruits or nuts. The fruit and nut group (14.6 million are imported each year) is subject to stringent regulation because agricultural producers have long recognized the pest risk associated with such imports. However, imports of roses (11.6 million per year) and rhododendrons (2.6 million) are less tightly regulated.
Imported rhododendrons can carry infectious diseases, such as sudden oak death, that wreak havoc on forests in the U.S. Photo credit: suddenoakdeath.org.
The pest risk associated with these imports is highest in those regions that receive the largest numbers of imported plants. When considering rhododendrons, Michigan and Ohio together received 18 percent of the imports (471,000 plants); New York and New Jersey together received 14 percent (369,000 plants); Maryland and Virginia together received 10 percent of the imports (274,000 plants); and Oregon and California each received 9 percent (232,500 and 247,000 plants, respectively). In fact, sudden oak death was introduced to a California rhododendron nursery in the late 1980s.
Most of these plant imports transported by ship entered the U.S. in one of three cities: 37 percent through Los Angeles, 23 percent through New York City, and nearly 12 percent through Miami. Plants shipped to New York and Miami tend to come from source ecosystems similar to those in the receiving region, thus increasing the likelihood that a damaging pest will establish. While conditions around Los Angeles are less suitable for plants that host pests from the moist regions where the plants originated, many areas of the region are irrigated artificially, and thus might contain suitable hosts.
Of course, these imported plants don’t remain at the ports, but are sent to retail outlets for sale. Large retailers that probably sell imported rhododendrons, roses and other types of plants are found in California, Florida, New Jersey and Connecticut, as well as Washington, New York, Pennsylvania, and Maryland.2 Dispersal of imported plants through these outlets and other economic links between the urban metropolitan areas and surrounding rural areas facilitate the establishment and spread of any pests associated with the imported pests.
1Data on import volumes of particular types of plants are from Colunga-Garcia M., R.A. Haack , R.D. Magarey, D.M. Borchert . (2013) Understanding trade pathways to target biosecurity surveillance. In: Kriticos DJ, Venette RC (Eds) Advancing risk assessment models to address climate change, economics and uncertainty. NeoBiota 18: 103–118. doi: 10.3897/neobiota.18.4019; or were provided by Manuel Colunga.
2Colunga-Garcia M, Haack RA, Magarey RD, Borchert DM (2013) Understanding trade pathways to target biosecurity surveillance. In: Kriticos DJ, Venette RC (Eds) Advancing risk assessment models to address climate change, economics and uncertainty. NeoBiota 18: 103–118. doi: 10.3897/neobiota.18.4019