Winegrapes and pests

Vineyard Fruit Fly Alert:

Drosophila flies and their possible impact on winegrapes

Vaughn Walton, Ph.D., Horticultural Entomologist, OSU

Spotted Wing Drosophila, (SWD, Drosophila suzukii), has renewed our interest in the impact of fruit flies  on crop quality. Since the fall of 2009, several studies have been conducted to determine fruit fly impacts on winegrapes in Oregon. In 2013, limited impacts have been found due to preventative vineyard practices and optimal weather.  Consistent with previous years, it appears that fully intact berries have limited susceptibility to SWD attack. Some growers are experiencing increased berry cracking due largely to recent rain events. These berries may show increased incidence of disease which can be an indicator of Drosophila melanogaster (common vinegar fly) activity. We are providing a brief update on our findings from berries potentially impacted by fruit flies this year:

Cracked berries often result in large numbers of Drosophila spp. flies, including SWD, feeding on lesions, and this phenomenon may cause concern. Data collected from several vineyards during 2013 show some egg laying and larval presence of Drosophila spp. flies in cracked berries. Surveys conducted from 2009 to 2013 found that both SWD and Drosophila melanogaster were inside compromised berry tissues. Larval rearing has shown that D. melanogaster are the most commonly found species in winegrape tissues that are compromised.

Drosophila melanogaster is known to be associated with common spoilage bacteria such as Acetobacteria. Very little is known about the contribution of SWD to this phenomenon, as SWD is known to attack only ripe, fully intact fruit. Research is currently being conducted in order to determine the importance of D. melanogaster and D. suzukii in spreading spoilage bacteria.

In certain cases, where berries have already cracked, there may be value to manage Drosophilid flies and limit the spread of Acetobacteria using registered pesticides. For recommendations regarding effective fruit fly management options, please consult the grape section of the Pacific Northwest Pest Management Handbook and the Spotted Wing Drosophila website for information on identification, monitoring and management of D. suzukii (http://spottedwing.com). Be aware that treating tissues such as cracked berries may increase the residual activity of pesticides. Adding a day or two to the pre-harvest interval (PHI) may be prudent when treating cracked berries. For more information regarding disease management, see the 2013 Pest Management Guide for Wine Grapes in Oregon.

For more information and to determine the best management practices, contact your regional extension horticulturist, pest consultant, or Vaughn Walton (waltonv@hort.oregonstate.edu), ph: 541-740-4149).