Vine Size: Magic Number 15
Magic number 15: Yesterday’s pic of the day talked about crop load balance being a function of vine size and pruning/thinning levels and that the magic crop load target for NY Concord vineyards was “15.” So what does that mean and what happens when the vines don’t hit the target?
“Crop load” is the crop size relative to vine size. Crop size pretty direct…the weight of the fruit on the vine. Vine size is the weight of one-year-old dormant cane prunings. We already established that pruning weight is directly related to vine leaf area and total vine growth, so it is an estimate of vine capacity. As a practical tool, we measure “crop load” by the Ravaz Index = crop weight/pruning weight. It indicates how much crop is on the vine compared to how much the vine can handle.
Concord vines with a Ravaz Index of 15 will reach 16 Brix by the early to middle part of the commercial harvest season and will neither gain nor lose pruning weight. They are subjectively considered “balanced.” The fruit reaches the desired quality and you start and end the season with the same vine capacity and same yield potential for the next season.
Vines with more than 20 pounds of fruit for each pound of pruning weight (a Ravaz Index > 20) are considered overcropped and will have delayed ripening and will lose vine size, thus reducing yield potential for the next season.
Vines with less than 10 pounds of fruit for each pound of pruning weight (a Ravaz Index < 10) are undercropped. They will have high fruit maturation and will gain pruning weight. This is a good strategy if you are trying to build vine capacity but it is less profitable in the current season because the vine could have ripened more crop while maintaining pruning weight.
Our research also indicates that the response of Concord fruit and vine growth to crop load is the same whether the crop management was done through pruning only or through light pruning with fruit thinning. This opens the door for more more mechanized approaches to crop load management.
