US (CA): Heat affects Central Valley grapes

Several weeks of high temperatures in California's Central San Joaquin Valley have affected table grapes in the region. The heat has had an effect on the sugar content, maturation and colouring.

High temperatures in the valley have reached or topped 100 degrees for most of the month of July, and that intense heat has sped up fruit maturation. The lack of water the state's growers have had to deal with has also compounded the situation. As Nick Dulcich, of Sunlight International, explained, the drought means there's less water for vineyards, and dry conditions in the fields have augmented the heat's effects.

“We usually run water down the furrow in the middle of the rows and get grass growing in between,” said Dulcich. “But because we have less water due to the drought, the soil is dry in the field and there's no absorption of that heat, so it's just pure heat on that dirt. It's stopped the colour, it's advancing the sugars and some varieties are coming abnormally early.” He pointed to the Princess variety as an example of the effects of the heat. While that variety doesn't usually come on until August, this year Sunlight will be done with the Princess by July 22 – a full two weeks before it's usually available. In addition to speeding up maturity, the heat has also been upping sugars.

“Brix for Summer Royal grapes are usually around 18 or 19,” noted Dulcich, “but we've measured them at 27 this year, which is unheard of.” While sugars may be up, the timing to get good colouring on the grapes has been thrown off.

“We've got fruit that's got 15 percent colour and 19 brix, and if the fruit doesn't get the right colour it doesn't make it to market,” said Dulcich. “We're worried because, if you look at Scarlet Royals, they have 60 percent colour and a lot more sugar than you'd think. It's a timing thing, and the heat hit at a time when it affects colour.”

For more information:
Nick Dulcich
Sunlight International
+1 661 792 6360

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