Grad student Geoff Hall with a bunch of shriveled grapes.
The bright sunny days and cool nights of autumn so perfect for ripening wine grapes in Washington may also be fostering the vineyard villain berry shrivel, according to Markus Keller, Chateau Ste. Michelle Distinguished Professor of Viticulture at WSU’s Irrigated Agriculture Research and Extension Center at Prosser.
Characterized by the sudden shriveling of berries while the stem remains green, berry shrivel can cost growers up to 40 percent of a crop, Keller said.
“The berries start to ripen, then very suddenly decide they’ve had enough and start to shrivel,” he said. “The problem is it is very unpredictable. It only happens in some berries, in some bunches, in some vines, in some blocks, in some years. It is a moving target.”
Berry shrivel is most prevalent in certain varieties, such as Cabernet Sauvignon, Sauvignon Blanc and Petite Syrah.
“We almost never see it in Merlot or Chardonnay grapes,” Keller said. Because it lowers sugar content, fruit with shrivel is very sour.
Unfortunately, the only way to remove the sour grapes is to remove the impacted clusters by hand.
“So not only do growers lose the fruit, they have to pay people to clean the crop,” he said. “Economically, it’s a double whammy.”
Washington growers first alerted Keller to the problem in 2003-04.Working with grant dollars from the Wine Advisory Committee, he, fellow WSU faculty member Bhaskar Bondada and graduate student Geoffrey Hall have been exploring a number of possible causes for berry shrivel.
“We have followed berry shrivel throughout three entire seasons to see if there are any preliminary symptoms – early signs that berry shrivel is there,” Keller said. “We’ve tagged specific plants and specific clusters in blocks where berry shrivel has been prevalent in the past; but as is the case with these things sometimes, the clusters we tag are fine and the ones right next to them are shriveled.”
Based on an analysis of grapes with berry shrivel, Keller and Hall have confirmed that it includes an arrest of ripening. Bondada has reached the same conclusion based on his studies of the anatomy of impacted plants. Specifically, he is examining the physiology of vascular pathways in the plant that involve moving water and sugars into the berries.
“Thus far, my research has shown that most flesh cells of berries with berry shrivel have lost their membrane integrity, whereas the cell membranes were intact in the healthy berries,” Bondada said. He noted that both macro and micro nutrients – on a per fruit basis – were lower in the shriveled berries than in healthy berries.
Bondada also found that the vessels that make up the plant’s plumbing system in afflicted canes often were blocked with tylosis, a balloon-like obstruction, and that the stalk of clusters with berry shrivel showed a wavy architecture different than that of healthy plants.
The next step is to explore what causes this, as well as possible preventives or treatments.
The team is focusing on the impact of temperature and light changes.
The team is focusing on the impact of temperature and light changes.
“The bright, sunny days and cool nights have always been considered an advantage for Washington growers,” Keller said. “But, if the nights are too cool it could induce plants into thinking winter is just around the corner and they need to be focusing their energy on winter hardiness rather than fruit production. That’s our current working hypothesis.”
Some scientists in Europe and California also have spent a lot of time looking for a pathogen or disease that might cause berry shrivel.
“They have run a lot of tests, but so far no one’s been able to identify a pathogen,” Keller said.
Bondada noted that berry shrivel also has been reported in British Columbia, Chile, Austria, Germany and Italy.
