According to Michigan State University Extension, two important nursery crops, boxwood and cultivated roses, are experiencing increased disease pressure that results in unsalable product and lost profits for growers. Boxwood blight is caused by the fungus Calonectria pseudonaviculata and initially causes brown lesions on leaves that can spread the entire plant and result in its death. Control methods include removing dropped leaves from under plants, isolating new shipments, alternating large quantities of Buxus spp. with non-host plants and spraying preventative fungicides. For more information on boxwood blight, visit the Pacific Northwest Disease Management Handbook or MSU Extension’s bulletin, “Boxwood blight disease identified in North America.”
Roses are a major ornamental nursery crop accounting for approximately $650 million in gross sales in 2012. Rose rosette disease is caused by a virus vectored by the mite Phyllocoptes fructiphilus that affects multiflora roses (Rosa multiflora) and is the most prevalent in the western United States. It causes rapid stem extension, heavy thorn density, unusual red shoot growth and plant stunting. It is important to be vigilant upon inspecting cuttings and rootstocks coming into grower’s facilities. More information can be found through Greenhouse Grower’s “Reducing the Spread of Rose Rosette Disease” and Kentucky Cooperative Extension’s Rose Rosette Disease fact sheet.
Impatiens downy mildew continues to be a challenge in greenhouses and landscapes around the United States. Identified in greenhouse facilities in multiple counties this spring in Michigan, a stringent preventative spray program will need to be implemented by all growers. The fungus-like organism, Plasmopara obducens, initially causes subtle yellowing especially on the upper leaves of plants, fluffy, white growth on the underside of leaves, leaf curling, stunted plants and eventually leaf and flower drop. Upon infection, impatiens plants and those within 3 feet of the infected plant should be discarded in a plastic bag to prevent further losses in the facility. Numerous articles can be found at MSU Extension, including “How to manage impatiens downy mildew in the landscape” and “Impatiens downy mildew: Outbreaks reported in Michigan and nearby states.”
Control of these and other pathogens requires scouting, vigilance, research and education to prevent outbreaks and product loss. Funding for grants through the Specialty Crop Research Initiative and Specialty Crop Block Grants are strongly dependent on the Farm Bill’s passing through Congress before the deadline of Oct. 1, 2013.
For current updates on these and many other current topics affecting our industry, visit the American Nursery and Landscape Association’s (ANLA) Knowledge Center.
Source : Michigan State University News Release