Update on 2010 statewide survey for blueberry scorch and blueberry shock diseases
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
The Michigan Department of Agriculture (MDA) has recently completed a large-scale survey of Michigan blueberry fields to provide for early detection and eradication of blueberry scorch and blueberry shock diseases of blueberry in the state. Blueberry shock and blueberry scorch are caused by specific plant viruses, which are detrimental to blueberry plants but are not harmful to people. Random leaf sampling was done on Michigan blueberry farms of growers who volunteered for the survey. Fields at sites where these viruses were detected in 2009 were also intensively sampled. Samples were tested by ELISA (enzyme-linked immunosorbent assay) in the laboratory. More than 28,000 samples were tested in total.
The survey resulted in seven detections of blueberry scorch in three different areas of the state and no detections of blueberry shock. As you may recall, in 2009, blueberry scorch was detected in several commercial fields in west Michigan, and blueberry shock was found in a MSU research planting in Fennville, Michigan. In each case, infected blocks were removed and destroyed. Some of the positive samples in 2010 were in fields adjacent to last years’ infected fields. This suggests that some spread may have taken place by aphids. We are currently investigating the ability of the blueberry aphid (Illinoia pepperi) to vector blueberry scorch virus from infected to healthy blueberry plants to determine the risk of spread. The only other means of spread of this virus is via infected planting material.
It is likely that the detections represent multiple introductions of blueberry scorch virus into the state from areas where the disease is endemic (e.g., New Jersey or the Pacific Northwest). From the observed occurrence in a few older plantings of various cultivars, it appears that these introductions may have occurred years ago, before blueberry scorch was even recognized as a plant disease. A more recent introduction of blueberry scorch virus appears to have occurred via non-symptomatic nursery stock (cultivars Legacy and Hannah’s Choice) before blueberry scorch and shock viruses were included in the virus-tested nursery stock program. Known sources have been destroyed. Distinctive scorching symptoms may not be present, depending on the virus strain and cultivar. However, “Hannah’s Choice” plants showed poor growth and “Legacy” leaves had a pale green color and red line patterns in some cases.