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Emerging Invasive Plant Pests
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Phytophthora ramorum and Maryland
Updated March 10, 2010
An important disease called ‘Sudden Oak Death’ is caused by an exotic pathogen,
, which can cause rapid plant death. This pathogen is important because of its ability to survive prolonged heat in the form of tough spores, or mycelium in infected tissue, or in soil, and the ability to infect a wide host range of plant species (oaks, and other landscape and forest shrubs and trees).
The Maryland Department of Agriculture (MDA) has been continuously following up all trace forward lists provided by USDA, APHIS for exotic diseases, including
In addition, MDA has been conducting monitoring surveys for
for several years, including recent surveys from 2014-17. Until recently,
had been detected in some of the samples collected from a list of Maryland buyers (nursery and home owners) provided by USDA, APHIS. These buyers obtained the plant materials from a nursery which was found positive in an annual compliance survey. In the past,
had been detected in trace-forwarded samples only (one each year) in Baltimore, Prince George’s, and Montgomery Counties in 2004, 2009 and 2012, respectively.
Recently, the Maryland Department of Agriculture has been monitoring exotic pathogens such as
Kalmia, Pieris, Rhododendron and Viburnum in nurseries and grape phytoplasma in vineyards. For
surveys were conducted in 2014, 2015 and 2016 at 30 nurseries, landscaping companies, and big box stores inspecting 115,327, 34,206, and 15,032 plants, respectively. Of those plants, 578 in 2014, 266 in 2015, and 868 in 2016 exhibiting symptoms similar to those produced by
were collected and tested. Five percent of the 2014, 12% of 2015, and 23% of 2016 tested positive for
spp by ELISA test. In 2016,
was detected only in one of the nurseries surveyed, located in Howard County, MD. At this nursery, a total of 404 plants were inspected and 33 of which found symptomatic were collected, and tested, and 33% samples were found positive for
was discovered in one
‘Cunningham White’ (Fig 1) and in two mountain laurels --
‘Olympic Wedding’ (Fig 2 and 3). This was the first time
was detected in a nursery in Maryland.
Fig 1. Leaf spot and blight in
‘Cunningham White’, Fig 2. Leaf spot leading to blight in
‘Olympic Wedding’, Fig 3. Leaf blight leading to dieback in
The Maryland Department of Agriculture, in an attempt to track the source and potential spread of the disease, found that this nursery obtained plants from two different sources. Kalmia’ Olympic Wedding’ plants were obtained from another nursery in Maryland, and
‘Cunningham White’ plants came from a Oregon nursery. MDA also monitored this supplier nursery in Maryland and contacted Oregon to find a possible source of the pathogen, but no identifiable source for the disease was found. Twenty-three homeowners in Maryland purchased the same plant cultivars from this infected nursery and of those, one
‘Cunningham White’ tested positive for
in one of the homeowners’ sites.
This occurrence shows the need for nurseries, landscapers, and homeowners growing
susceptible plants to be alert for possible symptoms as shown in the pictures.
Maryland Department of Agriculture, in collaboration with USDA, PPQ, and the involved nursery destroyed all infected plants and cleaned the affected area of the nursery and homeowner’s sites, following USDA’s protocol. MDA continues to participate in national surveys of nurseries and the environment to gather information on the potential entry and spread of
Please help us keep our forests and nursery industry healthy and strong by excluding this devastating disease from our state. All materials received from out-of-state sources by Maryland nurseries should be separated from other stock, especially suspicious plant materials until proven negative. This summer, 2017, MDA will continue monitoring this exotic disease at both the 2016 positive
nursery and homeowner sites for
. In addition, five nurseries in Maryland will be selected, samples of the five major host species will be inspected and all suspects will be tested. If nurseries or plant dealers are concerned and would like to have plants sampled, please contact MDA at 410-841-5920. Our nursery inspectors will visit your nursery as quickly as possible. All Maryland homeowners, if you have suspicious plants, contact Maryland Cooperative Extension’s Home and Garden Information Center, http://www.hgic.umd.edu/ for more information. The results of these efforts will be posted on this site as they become available.
Nurseries, plant dealers, and landscapers that are not contacted or visited by MDA are not restricted from selling host plants from the regulated areas. Please be aware that additional establishments may be contacted or visited as more information becomes available.
on the West Coast, a USDA, APHIS Emergency Federal Order is in effect, restricting the movement of nursery stock from California, Oregon, and Washington nurseries. However, we strongly recommend that Maryland nurseries, landscapers, and plant dealers isolate all known host plant materials originating in these states separate from other shipments, in order to reduce the risk of spread to other plant material and to expedite any regulatory action that may be necessary if the source nursery is later determined to be infected with
For any questions or further information, contact firstname.lastname@example.org or the phone number provided above.
Pine Shoot Beetle
Thousand Cankers Disease
Emerald Ash Borer (EAB)
P. ramorum - (sudden oak death)
Euonymous leaf notcher, Pryeria sinica
Asian longhorned beetle
Maryland Invasive Species Council
North Central Pest Management Center Pest Alert
US Forest Service Sudden Oak Death Website
USDA APHIS Sudden Oak Death Website
Calfornia Oak Mortality Task Force
50 Harry S. Truman Parkway, Annapolis, MD 21401
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