HERB GARDENING ENTHUSIASTS CAN HELP DETECT INVASIVE PLANT DISEASE

HERB GARDENING ENTHUSIASTS CAN HELP DETECT
INVASIVE PLANT DISEASE

Since destructive pests are often impossible to control once established, early detection is key to stopping their spread


ARLINGTON, VA—April 7, 2010 – Until proposed revisions to the regulations governing international plant trade, currently under review, are approved by the U.S. Department of Agriculture (USDA), homeowners can play an important role in detection and reporting of invasive insects and diseases. New non-native plant pest introductions are detected at a rate of one every 12 days, adding to the burden of the approximately 400 tree pests already established in the United States. These pests can wreak havoc in homeowners’ yards, and then move through neighborhoods and to nearby forests, causing costly and widespread destruction.

The Nature Conservancy, along with nursery industry partners and scientists, is supporting these revamped regulations in its ongoing efforts to block non-native insects and diseases. If implemented, the USDA rules would create a new category called NAPPRA (Not Authorized for Importation Pending Pest Risk Assessment), under which the nation could quickly stop the import of some plants suspected of harboring pests until procedures can be implemented to ensure they are safe.

“Vigilant homeowners and gardeners have been the ones to detect the presence of foreign pests that had previously gone undetected in many areas,” says Faith Campbell, senior policy representative in the Conservancy’s Forest Health Program. “A Massachusetts homeowner, who found a strange-looking bug in her backyard and reported it to the appropriate government agency, helped prevent the Asian long-horned beetle from spreading through the United States.”

Earlier this year, an alert greenhouse owner in Pennsylvania saw odd symptoms on his seedling bay laurel or sweet bay (Latin: Laurus nobilis). Experts confirmed that the plants were infected by the pathogen that causes “sudden oak death” (Latin: Phytophthora ramorum), a disease that has killed over a million trees in California. This is not the first detection of the pathogen in Pennsylvania or the eastern United States; however, to date, there have been no detections of the pathogen in the forestry environment on the East Coast.

This disease is known to attack several kinds of oaks, magnolias, rhododendrons, and mountain laurel. Bay laurel is a popular herb often grown by gardeners. If homeowners have recently bought bay laurel seedlings or seeds, they should examine these plants carefully. If the plants have dead or dying leaf tips or the entire plants are dead or dying, those symptoms may be caused by:
· too much water
· too little water
· too much fertilizer
· chilling or freeze damage
· infection by the sudden oak death pathogen or some other disease agent

If homeowners rule out all the causes except for the presence of a disease, they should contact their state department of agriculture to find out where to send a sample of it and how it should be packaged to ensure spores cannot escape during shipment. A state’s chief plant pest regulator can be found at www.nationalplantboard.org/member/index.html.

Additionally, as homeowners nationwide begin their general yard clean-up and spring gardening, they should be aware that other plants and trees might be carrying a damaging insect or disease. If they notice any insects or a blight or disease they don’t recognize, they can take a photo or specimen of it to their local nurseries or use Internet resources such as http://invasivepests.org/photosmore.html to help them identify it. If they suspect they may have found an invasive pest or pathogen, they should contact the local government department that oversees agriculture or forestry to alert them to the discovery and gain assistance in confirming its identity.

Following are some of the most prevalent invasive insects and diseases, and the regions which are currently threatened by their encroachment.

Non-Native Pest Regions at risk
hemlock woolly adelgid ---- Appalachian Mountain region

laurel wilt & ambrosia beetle ---- coastal regions from South Carolina to Mississippi; Florida

sudden oak death ---- coastal regions of California and Oregon

Asian longhorned beetle ---- New England; New York and New Jersey; Chicago metropolitan area

More detailed information about and photos of these and other invasive pests can be found at http://www.invasivepests.org/.

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The Nature Conservancy is a leading conservation organization working around the world to protect ecologically important lands and waters for nature and people. The Conservancy and its more than one million members have been responsible for the protection of more than 18 million acres in the United States and have helped preserve more than 117 million acres in Latin America, the Caribbean, Asia and the Pacific. Visit us on the Web at http://www.nature.org/.

The Continental Dialogue on Non-Native Forest Insects and Diseases is a group of organizations and individuals that cultivates and catalyzes collaborative action among diverse interests to abate the threat to North American forests from non-native insects and diseases.

Phytophthora ramorum has been detected in Pennsylvania on Bay (Laurus nobilis)

Another pathway by which P. ramorum can be introduced is described below:

"On Feb. 18, 2010 the Penn State Plant Disease Clinic received a sample of Laurus nobilis, known commonly as bay laurel, true laurel, sweet bay,laurel tree, Grecian laurel, or bay tree. Some people use its leaves in cooking. The tips of the leaves submitted were dead or dying and it was reported by the grower that 95% of well rooted plants in 12 or so flats exhibited the symptoms. The United States Department of Agriculture-Animal Plant Health Inspection Service (USDA-APHIS) confirmed the plants to be infected with Phytophthora ramorum, the Sudden Oak Death pathogen known to occur in trees and shrubs on the west coast of the U.S. and in Europe. The sample came from a commercial, primarily wholesale, greenhouse in eastern Pennsylvania. Phytophthora ramorum can infect many important ornamental trees and shrubs under the right conditions. There is a great deal of concern that this fungus-like organism could cause significant economic damage to eastern forests and landscapes if not excluded from the region.The’ bay laurel’ submitted was not Umbelluiaria californica, the California bay or California bay laurel that grows on the west coast and is a major host of Phytophthora ramorum that then spreads to oaks. However, Laurus nobilis is known to be a host of Ph. ramorum.The actual source of the Ph. ramorum in Pennsylvania is still under investigation and is very much in question. The infected plants had been grown in Pennsylvania from seed obtained from a source in California. As yet, there are no known cases of Ph. ramorum being seedborne. I learned recently that the ‘seed’ is sometimes received not as cleaned seed but as seed still in the drupe (fruit). That raises the possibility that the pathogen may have been in parts of the fruit other than the actual seed. It is also possible that the pathogen was infecting other plants in the greenhouse and spread to the Laurus. APHIS is doing ‘trace backward’ investigations to determine where the pathogen may have come from and‘trace forwards’ to determine whether various plants sold by the Pennsylvania greenhouse are carrying the pathogen.

Phytophthora ramorum has, to date, been excluded from the eastern U.S. but this occurrence may indicate that the plant pathogen is now or will soon be in the region from multiple sources. In 2009, Laurus nobilis was named as the Herb of the Year by the International Herb Association (IHA). Laurus nobilis seed can be purchased from a number of sources including through Amazon.com. Web information indicates that the seed is difficult to germinate. It is my understanding that people have been encouraged to grow this plant and that it has been used in various Master Gardener projects. If seed or tissue associated with seed is actually the source of the pathogen, it is possible that Phytophthora ramorum has arrived in the east with seed purchased bybackyard gardeners, etc. Where is the ‘failed to germinate’ material discarded? Where are plants with dying leaf tips discarded? The photo below (and attached) is of the actual sample as it arrived at Penn State. It is not very impressive. If you are presented with Laurus nobilis plants with dead or dying leaf tips or entire plants dead or dying…those symptoms may be caused by:

too much water

too little water

too much fertilizer

chilling or freeze damage

Phytophthora ramorum infection

There is much we don’t know about the circumstances surrounding this occurrence and, therefore, we can’t release specifics such as the name of the greenhouse. But, the information above can be used in newsletters,training sessions, news releases, grower presentations, etc."

Gary W. Moorman, Prof. of Plant Pathology

The Pennsylvania State University, Department of Plant Pathology

Shift in Phytophthora ramorum populations in Washington State

The EU1 strain is now the most common P. ramorum lineage detected in WA state nurseries and non-nursery sites, with a concurrent rise in NA2 and decrease in NA1. Evaluation of genotypes over the past 5 years by Gary Chastagner, Katie Coats, and Marianne Elliott at Washington State University shows the reversal in genotype frequency occurred in 2008 and persisted into 2009. They detected EU1 in 99 positive samples at seven locations, NA1 in 17 samples at four sites, and NA2 in 48 samples at three sites in 2009. In contrast, the first year of the study (2005) identified four EU1 samples at one site, 103 NA1 samples at 14 sites, and 12 NA2 samples at five sites.
Of the 46 Washington nurseries found positive since 2003, five had infected plant detections in 2009. Twenty nurseries have been confirmed positive at least two years. Two of these sites were found to have positive plants three different years and two sites were positive four years. Genotype analysis has been performed on samples from 31 nurseries since 2005. Of the nurseries with multiple confirmed years, six had various combinations of two lineages for one or two years and one had a year with all three lineages followed by two other years with two lineages present each year.
Nine Washington non-nursery sites (landscapes, water, soil or trace-forward landscape plants) have also been identified P. ramorum positive since 2005, with seven sites having been positive in 2008 and/or 2009. Of the seven sites, the Rosedale Stream (Pierce County) has been found positive for four years (NA1) and the Sammamish River (King County) has been confirmed positive for three years (several lineages). A Pierce County site with NA2-positive salal plants was also found adjacent to nursery property, and four residential sites have been found in the past two years, all of which have been identified with the EU1 strain (two residences were found with the EU1 strain in 2008 and 2009, one with plants and soil, and one with just soil). These four residential sites were trace-forwards from the same EU1-positive nursery.
In 2009, a new systematic sampling method was implemented, which involved not only genotyping the original DNA sample, but also a second round of sampling using the same plant and/or bait material from which the DNA positive was detected. In addition, through a cooperative effort with the Washington State Department of Agriculture and the USDA Animal and Plant Health Inspection Service (APHIS), a third round of sampling was performed on whole plants or plant material collected from most of the nurseries prior to destruction of the plant material. This duplicate and triplicate sampling allowed for a better representation of the genetic distribution of the P. ramorum population.
In total, 450 samples from 31 nurseries, three water sites, and six landscape locations have been analyzed. For more information on the study and its findings, contact Gary Chastagner at chastag@wsu.edu.

From the COMTF March newsletter

New species added to the host list

Ten species have been added to the list of federally regulated P. ramorum associated host plants. The USDA Animal and Plant Health Inspection Service (APHIS) issued the on 2/22/10, adding Mexican-orange (Choisya ternate), kousa dogwood (Cornus kousa), Daphniphyllum glaucescens, European holly (Ilex aquifolium), Japanese-oak (Lithocarpus glaber), Magnolia cavalieri, Magnolia foveolata, bayleaf currant (Ribes laurifolium), bilberry (Vaccinium myrtillus), and lingon berry (Vaccinium vitis-idaea) to the list. Symptoms for each of the new hosts other than bilberry were leaf necrosis. Tip dieback occurs in infected bilberry as well as Daphniphyllum glaucescens These species were identified as susceptible by the Canadian Food Inspection Agency (CFIA) and the United Kingdom's Food and Environment Research Agency (FERA).
Nurseries currently operating under an APHIS P. ramorum compliance agreement are able to continue shipping hosts and associated plants, including the newly listed plants; however, any nurseries not currently under a compliance agreement that contain these new species must be properly inspected, sampled, tested, and placed under a Compliance Agreement by 3/31/10 in order to be able to move any plants interstate.

From the COMTF March newsletter

News from California and the rest of the US

Warm, wet weather caused by El Nino is a "free ticket to Disneyland" for P. ramorum in California, providing an environment in which the disease can spread:

http://www.napavalleyregister.com/lifestyles/home-and-garden/columnists/bill-pramuk/article_60416e9e-184e-11df-bfaf-001cc4c002e0.html

Researchers at University of North Carolina are developing a model to predict spread of P. ramorum if it were to get loose in the eastern US:

http://www.newsobserver.com/news/local_state/story/314528.html

NA2 lineage found on salal, additional positive nurseries

As part of the perimeter survey conducted at a P. ramorum-positive retail nursery in Pierce County, Washington last summer, the Washington State Department of Agriculture identified infested salal (Gaultheria shallon) plants in the natural landscape (as reported in the COMTF August 2009 Newsletter). Follow-up analysis of the samples by the Chastagner lab at Washington State University has resulted in the isolation of the NA2 lineage from the salal. This is the first detection of the NA2 lineage on native forest vegetation. For more information on this development, contact Gary Chastagner at chastag@wsu.edu.

Washington had two P. ramorum-positive locations identified in January. Both sites have previously been found positive for the pathogen. One positive find was in retention pond water at a Pierce County retail nursery. Treatment of the pond (located on nursery property) is optional as it is not used for irrigation or fire suppression. The second site was in a Mason County church landscape where an assumed-positive Viburnum tinus was identified as part of a Thurston County nursery trace-forward investigation. Follow-up efforts have determined that the viburnum did not transit through the Thurston County nursery, but rather was sourced from Oregon. It is unknown where the plant potentially became infested. The Oregon nursery from which the plant originated completed the CNP in December (2009). WSDA PCR results on the viburnum were inconclusive; results are pending from Beltsville, MD.

From the February COMTF newsletter

Japanese larch and Western hemlock new hosts for P. ramorum in the UK

"Since August 2009, significant numbers of Japanese larch trees have begun to show symptoms of needle loss and dieback in Devon, Cornwall and Somerset. The number of trees affected, and the apparent speed of the decline is a cause for concern – some trees are already dead. Smaller numbers of broadleaf trees associated with the larch were found to have symptoms of bleeding cankers, and closer examination by Forest Research scientists revealed that these broadleaf trees were infected with Phytophthora ramorum. This is the fungus-like pathogen responsible for the phenomenon known as “sudden oak death” in the USA, where it has killed millions of trees including the native American tanoak. "

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