Jun 3, 2015

Assistance in raspberry virus diagnosis offered

In recent years, an increasing number of raspberry growers have reported seeing berries that are smaller than usual, misshapen and crumbly when harvested, particularly in older fields. They may have been of such poor quality they were not marketable. The canes and leaves appeared normal in some cases while in other cases plants showed yellowing and stunting. It is difficult to determine the reason for crumbly fruit as there are multiple possible causes. For instance, poor pollinating weather or an inadequate number of bees may result in a reduced number of drupelets. Tarnished plant bugs can also cause crumbly fruit by feeding on flowers or developing fruit. As a result, some drupelets do not develop and berries become irregularly-shaped, small and crumbly. Regular scouting can help determine if tarnished plant bugs are to blame, whereas weather data and observations on bee numbers may also help sort out pollination issues. However, viral infections by viruses can only be confirmed by laboratory tests. In 2014, leaf samples from a problematic Michigan raspberry field were tested and found to contain tomato ringspot virus and raspberry bushy dwarf virus. Both can be a cause of crumbly fruit.

To assist raspberry growers in determining possible viral causes of production problems, a survey will be conducted this summer in Michigan raspberry fields for viruses as part of a project funded by the Michigan State Horticultural Society. Growers who have seen symptoms in their fields in the past such as crumbly fruit, low vigor or leaf yellowing are invited to participate as well as anyone who is suspicious of viral problems in their fields. We will collect samples when symptoms become apparent in mid- to late summer and will have them tested at Agdia, Inc. in Elkhart, Indiana, for a range of viruses, including raspberry bushy dwarf virus, tobacco ringspot virus and tomato ringspot virus. The tests will be free to growers and samples will be treated anonymously. Participating growers will receive a full report on their samples when tests are completed. A final report, which will be presented at the Great Lakes Expo, will only present the results in aggregate (individual results will remain anonymous).

Please contact your local Michigan State University Extension educator or myself at [email protected] if you would like to participate in the survey or have any questions. You can also reach the MSU Small Fruit Pathology laboratory at 517-355-7539.

— By Annemiek Schilder, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences