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DISEASES OF REGULATORY CONCERN

Chrysanthemum White Rust (Puccinia horiana)

Chrysanthemum white rust (CWR) is a USDA quarantined plant pathogen that poses a potential trade barrier to growers of chrysanthemums in Virginia if introduced. The disease also poses a risk of increasing management costs if introduced into the Commonwealth as control of this pathogen requires weekly fungicide applications. For these reasons, VDACS plans to continue monitoring and eradication efforts to keep this pathogen out of the Commonwealth. In 2009, an estimated 15,000 Chrysanthemums were inspected state-wide by VDACS nursery inspectors for CWR. In 2010, over 100,000 plants were inspected by VDACS.

Ramorum Foliar Blight/Sudden Oak Death (Phytophthora ramorum)

Phytophthora ramorum was first identified in North America in 2000 as a lethal stem canker disease of oaks and tan oaks in the central coastal range of California. In 2001, the pathogen was also found associated with ornamental nursery stock causing foliar and branch dieback to hosts such as rhododendrons, pieris, kalmia, camellia and viburnum. This pathogen can be spread in nursery stock, poses a potential threat to forest ecosystems, and could impact the movement and trade of nursery and forest products if introduced into Virginia. VDACS is currently conducting extensive statewide surveys for this pathogen in an effort to detect P. ramorum before it can become established. Early detection is vital to successful eradication efforts in the event P. ramorum is introduced. Each year approximately 1,200 P. ramorum samples are collected and tested by VDACS. These include symptomatic foliar samples as well as soil and water samples.

Plum Pox Virus

Plum pox is a viral disease caused by the plum pox virus (PPV), which can infect most ornamental and agriculturally significant species in the genus Prunus,including fruit trees such as plums, peaches, and apricots. Ornamental species of Prunus may show few symptoms of plum pox virus but can be carriers of PPV. In commercial stone fruit orchards the disease blemishes fruit, reduces yield and quality, and is considered the most devastating disease of stone fruit in Europe.

The disease was first described in Bulgaria in the early 1900s and has since spread throughout Europe. PPV was first reported in North America in Adams County, Pennsylvania in 1999 and in Ontario and Nova Scotia in 2000. In the U.S., control efforts were thought to have eradicated the disease, but during 2006 surveys, the virus was found again on commercial plums and peaches in Niagara County, New York, on commercial peaches in Pennsylvania, and in a plum research plot in southwestern Michigan. Additional surveys conducted in 2007 and 2008 have since detected PPV in three New York counties and 9 additional properties in Ontario, all within the greater Niagara region. In 2010 VDACS sampled 2,000 trees state wide for PPV. PPV has not been detected in Virginia.

Potato Cyst Nematodes

There are two species of potato cyst nematodes (PCNs) – the pale cyst nematode (Globodera pallida) and the golden cyst nematode (Heterodera rostochiensis). Both species are thought to be native to regions of the Andes mountains, the center of origin of potatoes. PCNs were likely introduced to Europe around the 1850’s on stock collected for genetic improvement trials after the great potato blight of 1845. Both pathogens feed on potato roots which causes significant reduction in tuber yield and plant health. PCNs were not detected in the U.S. until 1941 when the golden nematode was discovered in Long Island, NY potato fields.  In 2006, the pale cyst nematode (Globodera pallida) was detected in soil from an eastern Idaho potato grading facility. The find caused Canada, Mexico, and Korea to temporarily ban the import of potatoes from Idaho while Japan stopped importing potatoes from the entire United States.  Most countries lifted bans on U.S. potatoes only after intensive surveys were conducted throughout Idaho showing infestations were localized. Since 2007, VDACS has tested 420 soil samples for PCNs, representing 420 field acres. PCNs have not been detected in Virginia.

Thousand Cankers Disease

Thousand Cankers Disease (TCD) is a disease complex of walnut, Juglans spp. which is caused by the fungus Geosmithia morbida and is vectored by the walnut twig beetle, Pityophthorus juglandis. The fungus causes the development of cankers beneath the bark of the tree.  As beetles attack the tree the number of cankers increases until they coalesce to girdle twigs and branches, restricting the movement of nutrients and eventually killing the tree. Thinning or dead branches will initially occur at the top of the tree, which will die from the top down. Trees may be infested for many years before showing symptoms.

Contact
Norman Dart
804.371.5086
Plant Pathology Lab, RM 229
600 North 5th St., Richmond, Virginia 23219
Norman.Dart@vdacs.virginia.gov

Click here for Office of Plant Industry Services contact information.


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