Cherry green ring mottle virus confirmed in tart cherry in Northwest Michigan
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.
We have received confirmation of our diagnosis of green ring mottle virus (GRMV) in tart cherry samples obtained from northwest Michigan this past July. Symptoms of green ring mottle virus infection are usually expressed in late June to mid-July. The main symptom of the infection is bright yellow leaves with circular green blotches. These infected leaves can be easily removed from trees during shaking at harvest, or will defoliate naturally. In 2010, defoliation approached 40-50 percent of the leaves on each affected tree. Green ring mottle virus symptoms appeared sporadically this year (one to a few infected trees per block). Sometimes fruit is affected by green ring mottle, and will look indented with streaks of dead tissue to the pit. We did not observe any fruit symptoms in 2010.
The first year that symptoms of virus infection are expressed in trees is typically the worst (“symptom burst” effect). In subsequent years, virus disease symptoms are usually reduced and reach a more moderate level. There is no cure for virus infection, and trees with green ring mottle virus symptoms in 2010 will continue to harbor the virus. However, we do not know what environmental conditions led to the outbreak observed this year. Thus, we do not know if green ring mottle virus-infected trees will appear symptomatic in 2011.
Natural spread of green ring mottle virus is very slow, and appears to occur tree-to-tree via root grafts. The virus is also spread by grafting at the nursery stage. Indeed, with virus indexing, we should not be seeing this disease in virus-free nursery stock. We currently do not know the source of the green ring mottle virus infections observed this year, or if the virus could possibly be vectored by an insect. We will be on the lookout for green ring mottle virus symptoms in 2011 and, if they appear, we will be assessing orchard blocks for evidence of spread of the virus and examining mechanism(s) of spread.
Dr. Sundin’s work is funded in part by MSU‘s AgBioResearch.