Skip to main content

Tracking Down the Causes of Bunch Stem Necrosis in Grapes

Late bunch stem necrosis, indicated by shriveling
of the stem, followed by shriveling of the
berries, in that order. Photo: Annie Klodd.
Author: Annie Klodd. Late bunch stem necrosis (LBSN) is a physiological disorder of grapevines, where the grape clusters shrivel and die during ripening. It is not a disease, so fungicides are not effective on it. However, a large part of what makes this disorder so frustrating is that the causes are not well understood. In collaboration with grape growers and the UMN Grape Breeding lab, we are working to identify potential causes so that we can develop recommendations to control LBSN.

Late bunch stem necrosis is a complex physiological disorder of grapevines, where the bunch stems (rachises) shrivel during ripening, followed closely by berry shrivel. This sudden change is frustrating for growers, when seemingly healthy vines produce unusable clusters. LBSN affects vineyards worldwide, but may be caused by a number of environmental stresses. This means that developing treatment recommendations is a complex, long-term task that may vary by vineyard.

Some potential environmental causes of LBSN, which have been proposed by previous studies in other parts of the world, include:

  • Mg, Ca, or N imbalances in the soil
  • Cooler-than-average, rainy weather during ripening
  • Wet, poorly drained sites
  • Excessive pruning
  • Unhealthy vines
This summer, we conducted preliminary research on four Minnesota vineyards this summer that reported severe LBSN symptoms. Based on our results, it is more likely that LBSN in Minnesota is due to cool, wet conditions and vine management, rather than soil nutrient imbalances. Soil tests and foliar nutrient tests did not reveal any evidence of nutrient imbalances or deficiencies at any of the vineyards we studied. On the other hand, the locations of the vineyards did experience relatively cool, wet weather from 2016-18, when LBSN was reported. 

Read the full article here, on the UMN Grape Breeding and Enology blog.

Identifying the cause of bunch stem necrosis is complex, and may require multiple field seasons in order to examine multiple factors and test management options. Pending funding, we hope to be able to provide recommendations for Minnesota grape growers.

Print Friendly and PDF