From the Press Democrat:

Grape growers are watching the weather reports with dread.

The late-season downpour hitting Northern California is threatening to devastate this year’s grape crop, making it potentially the third weather event in the last four years to wreak havoc on vineyards.

Most vineyards across Sonoma County are now in some stage of bloom, a process where plants engage in the delicate dance of self-pollination in order to fertilize the eggs that will become grapes.

Rainfall in June, which forecasters predict could set a new record, is expected to lower the amount of grapes that vineyards produce, potentially costing Sonoma County growers tens of millions of dollars in lost revenue at a time the industry continues to suffer economically.

Grapevine fertilization is timed to normally occur after the rainy season. But the late rain this year is hampering the process, preventing some grapes from forming.

For more, see: Weather interfering with grape pollination