Inception, Diagnosis and Consequences of the Berry Shrivel Disorder

Berry shrivel (BS) is a ripening disorder of unknown cause and sporadic appearance that has been increasingly observed in vineyards around California. BS has been mistaken for another disorder, bunchstem necrosis (BSN), but we have found that the disorders can be distinguished by the rachis of affected clusters. The rachises on BS clusters are green and healthy looking, while BSN rachises are brown necrotic. Much of the data presented here is from the 2005 growing season. This data had not been generated by report time last year. BS fruit has less sugar, lower pH, and reduced coloration several weeks before visible shriveling of the fruit. These differences are maintained throughout the ripening period. BS fruit stops sugar accumulation about two weeks prior to symptom appearance. The apparent rise in Brix of BS fruit after this point is due to fruit dehydration and solute concentration. BS affects a whole vine, as nonshriveled clusters on a vine with shriveled clusters are also compositionally different than fruit from a healthy vine. These ?likely to shrivel? (LTS) clusters have compositions intermediate between BS and healthy fruit. Nonshriveled clusters on a vine with BS clusters also stop, or slow, sugar accumulation at the same time as BS fruit does.

Since BS appears to be due to phloem dysfunction, girdling treatments were set up at different times in Davis and at the Oakville Experimental Vineyard (OEV) in Napa County. Artificially stopping sugar accumulation by girdling caused the berries to develop with reduced coloration and they eventually (3-4 weeks post girdling) began to shrivel.

There has been a trend at OEV for vines with a history of BS to be less water stressed (determined by leaf water potential) than control vines. To test the hypothesis that vine water status exacerbates or mitigates BS, an irrigation trial was set up in the Alexander Valley in Sonoma County. One treatment applied water at a rate that vastly exceeded the grower’s standard irrigation (approximately 5 gph as compared to 0.5 gph), and vines in the other treatment were not irrigated. These treatments affected vine water status, but they did not affect BS incidence in the vines.

The hormone CPPU (Prestige®) was sprayed at two concentrations (2 and 4 ppm) after set (8mm berry size) at two sites (OEV and Alexander Valley) to assess its effect on the incidence of BS and BSN. None of the hormone treatments had an effect on the incidence of BS or BSN.

BS can be propagated by chip buds. Budding was done in 2003, thus there was fruit for analysis in 2006. Vines propagated with buds from vines with a history of BS had reduced sugar accumulation, shorter shoots after budbreak, and reduced berry weight compared to vines propagated from healthy material.

Wines were made with the addition of different amounts of BS and BSN fruit in 2006 (0%, 5% and 10% by weight). The wines fermented to dryness and will be used for difference testing and descriptive analysis.