Current Berry Curve Information

(from the 9/3/2002 Lake Erie Regional Grape Program Crop Update)

The attached chart shows the current berry growth information for balanced (20+20) and minimal pruned Concord vines at the Fredonia vineyard lab. Although the berries were larger than normal during the typical thinning time around 30 days after bloom, the heavy crop in unfrosted vineyards and the dry weather have slowed them down to where they are smaller than they were at this time last year. On the 7/16/2002 crop update, I predicted 3.2 gram final berry weight in balanced pruned vines and 2.7 gram final berry weight in minimal pruned vines. As of right now, I am sticking with that prediction. However, the post-veraison increase in berry weight has a lot to do with vine water status from now until harvest (the more water, the greater potential berry weight). Therefore, if a September hurricane comes up the coast, the berries will be big. If we have a dry fall like 1998 or 1999, the berries will be smaller than predicted.

More on Leaf Photosynthesis
In one of the recent crop updates, I talked about sunlight and water being probably the two biggest limiting environmental factors to vine photosynthesis and ultimately production. The attached figure is photosynthesis data taken last week at the Fredonia Lab and illustrates the response of Concord vines to both light and water. Under low light conditions, all vines are photosynthesizing at the same (low) rate. We have more cloudy days and less total PAR than our Concord producing counterparts in Washington State, which is probably the reason they have higher production potential. Under full sun conditions, vines with adequate water can take full advantage of the sun's energy and maximize photosynthesis while vines under water stress start to close their stomates (to conserve water) and reduce photosynthesis.

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