PORTLAND - This year's harvest of Concord grapes could be one of the best harvests in more than a decade, however Mother Nature only did part of the work.
Researchers and viticulturists at the Lake Erie Regional Grape Project Center, located at 6592 West Main Road in Portland can confirm that growing conditions throughout the year, including record rainfall in June and mild, pleasant temperatures all through summer have contributed toward a robust harvest for Concord grapes this year. However, even though the conditions which were presented allowed the grapes to grow so well, growers still needed to understand how to best utilize and prepare for the conditions in order to get the best possible crop they could this year.
"Even though Mother Nature controls the weather that we're going to get, the growers still ultimately control the grapes," said Terry Bates, Lake Erie Regional Grape Program director and Cornell Department of Horticulture senior research assistant. "One of the things that the growers control is the number of buds that they leave during pruning during the winter. Each bud has a shoot, each shoot has so many clusters on it, and that helps set what the crop is going to look like. There is some human involvement: you can leave too few buds, or you can leave too many buds. Understanding how the weather might forecast will help growers better understand how much to prune, and growers are trying to best understand how many buds to leave on the crop."
According to Bates, the weather is a factor in how many buds grow per vine, as well as the number of clusters there are per bud, as well as how big those clusters are.
"If you're looking at clusters per bud, it has to do somewhat with what happened last year," Bates said. "Last year, we had a frost, and the crop size was low. Those buds developed as fully as they could have last year. There are close to 15 stages of bud development, and about half of those stages happen in the previous season. If you have good bud development in the previous season, you're going to see a higher number of clusters per bud. This year, our average clusters per node went way up because of last year's frost. The vines were not stressed from a crop perspective, and that allowed the buds to develop very well."
With regard to berries per cluster, the spring weather conditions have the largest effect.
"If the weather conditions are favorable to continue that bud development, which occurs in the spring, they obviously will," Bates said. "We had fairly good spring conditions, and the buds continued to develop. As a result, we had a higher-than-average cluster numbers per bud, and then when it was time for bloom, those flowers on those clusters set very well. As a result, the berries per cluster went up."
Consequently, the final factor weather has upon grapes is the weight of the berries, which is contingent upon what Bates calls a double sigmoid growth curve.
"Basically what happens is that the berries set going through bloom, then there is a rapid period of berry growth," Bates said. "You get this rapid increase, then about 40 days after bloom, it slows down, so the berries don't get any bigger. Then something called veraison happens, and the berries begin to get bigger again because they begin to swell with water. It's a curve that starts very quickly, then levels out, then starts up again."
Veraison can best be thought of as the stage which preludes the ripening of a fruit.
According to Bates, the first phase of the double sigmoid growth curve has a lot to do with cellular division. If the berries receive a lot of water during cellular division, the berries end up being bigger. Consequently, the first phase of the double sigmoid growth curve occurred during June, which experienced record rainfall.
"When you put all that together, we had high fruitfulness, because of the frost last year; we had higher berry number per cluster, so that increased the size of the clusters; and the berry weight itself was bigger because of all the water the berries received during cellular division," Bates said. "We call those the components of yield. Different conditions affect all of those differently, but fortunately, this year, they all affected them positively."
However, the berries still need to ripen, and that's where the growers have some control. Large, juicy berries are only beneficial if growers can ensure that all of their crop will ripen. Because the crop was so robust this year, many growers intentionally knocked berries off of the vine, so that the berries which remained on the vine would all have a good opportunity to ripen.
"If you have too much fruit, and you don't have enough leaves to ripen that fruit, the accumulation of sugar in the berries tends to be very slow," Bates said. "It can be so slow that the fruit never reaches the maturity level that growers want. In most years, it's not a problem at all - we set a big crop, it is appropriate for the year, and all the berries ripen just fine. However, some years, such as 2003, we had a big crop, there was a late bloom, a late ripening season, cool weather, and much of the fruit simply didn't ripen. This year, it's much of the same scenario, however the weather has been better. Bloom has been average, veraison was average, and ripening was average, but we set a big crop."
According to Bates, the weight of the berry 30 days after bloom is approximately half of what the final weight of the berry will be. By this measurement, growers have a general idea of how many berries should be knocked off of the vine in order to provide the remaining berries with a correct leaf-to-berry ratio, in order for all the berries to ripen to their full potential.
"If the crop is too big, and growers try to make the best decision possible, the growers will go out with a harvester and gently shake the vines," Bates said. "That way, at veraison time, the fruit has the perfect ratio, and this year, half of the growers in the area shook a portion of their crop off of the vine."