As the tallies are coming in this harvest, one thing across the board seems to be clear: there just isn’t very much fruit out there. Our own management company, which operates predominantly in West Sonoma, is clocking in around 50% normal yield. While that number is a little extreme compared to other areas, low yield seems to be a common refrain up and down the state.
How do we get to final yield?
In order to get to the bottom of this, I want to break up yield formation into three chapters: fruitfulness, fruit set, and sizing. Let’s work backwards in time:
Sizing: Beginning with berry sizing, sometimes you get through fruit set only to have berries put on minimal weight. Excessive water stress, heat events or periods of high evaporative demand (VPD, vapor pressure deficit) can reduce vascular water potential needed for berry growth and/or increase berry water loss from sizing fruit during the period from fruit set to lag phase. This is the most sensitive period for berry growth and hence for poor fruit sizing when conditions aren’t favorable. After veraison, these conditions can shut down or reduce sugar loading and lead to smaller berries, though the effect on final berry size is less pronounced than during initial berry growth.
Fruit set: Backing up a developmental step, prior to berry growth, poor fruit set or shatter is of course a regular occurrence these days, especially with budbreak occurring earlier and earlier in recent years. This year, shatter was prevalent in California due to a remarkably early budbreak and a chilly April and May.
The problem with 2026 wasn’t only poor fruit set, but rather poor fruitfulness to a larger degree.
Fruitfulness: Taking another step back in time, fruitfulness is basically what you start with. At flowering the year prior to any given season, future buds are already differentiating into cluster primordia, although the extent of differentiation is still debated. If you are concerned about fruitfulness for the coming year, as soon as canes are lignified you can send your buds in to be dissected and quantified for number of clusters and general size. Excessive shading or stress during bloom in year one can limit your fruitfulness in year two. I believe that the low yield we saw in 2022 was due to drought conditions in the Spring of 2021, although once everything fried on the vines that September, no one cared to quantify the total loss resulting from low fruitfulness.
