By Annemiek Schilder
Thanks to funding from the Michigan State Horticultural Society, we will again be able to provide assistance in diagnosing raspberry problems that may be caused by plant viruses. In 2015, we identified some virus infections that may be to blame for raspberry decline and “crumbly berry” symptoms in Michigan, such as infections with tomato ringspot virus and raspberry bushy dwarf virus. Symptoms include berries that are smaller than usual, misshapen and crumbly when harvested, particularly in older fields. They may be of such poor quality that they are not marketable. The canes and leaves appear normal in some cases while in other cases plants show yellowing and stunting and an overall decline.
Crumbly fruit from field-grown raspberries.
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 bug can also cause crumbly fruit by feeding on the 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 bug is to blame, whereas weather data and observations on bee numbers may help sort out pollination issues. However, viral infections can only be confirmed by laboratory tests.
