From the 7/19/2001 Crop Update:
It is one month past bloom and we have been estimating the crop at the vineyard lab. Once again the question has come up about berry weight at 30 days post bloom, 1200 growing degree days, or some % of final berry weight in crop estimation.
The way I like to calculate % final berry weight in crop estimation is to weigh a berry sample at the time I am thinning and make a prediction on what the final berry weight is going to be. I do this for two reasons: 1) the berry weight at 30 days after bloom and at the end of the season is different every year 2) the berry weight is changing very fast in the 30 day after bloom period (see the figure).
| Berry Weight (grams) | |
Here is an example. I did crop estimation on Monday morning (33 days after bloom) on 120 node vines at the lab. I weighed several berry samples and recorded an average berry weight of 2.0 grams. This seemed relatively large but it reflected the annual berry curve that Christine, Eileen, and Paula collect. I was past 30 days after bloom and well past the 50% final berry weight stage. Then came the fudge factor. I had to predict what the final berry weight might be at the end of the season. Given the relatively low crop and relatively large berries at this time compared to the past couple years, I made an educated guess that we would have 3.0 to 3.3 gram berries at the end of the season. That put my 2 gram berries somewhere in the 65% of final berry weight range. Therefore, when I stripped and weighed some vines, I multiplied the crop by 1.5 to get my predicted final crop (I did not multiply by 2 as I would if I were at 50% final berry weight).
Tom Davenport and I had the discussion that if the berries are 1.8 to 2.0 grams at 30 days after bloom that we have the potential of having 3.6 to 4.0 gram berries at the end of the season. My opinion is that it is possible but unlikely. Even in similar years of medium to low crops and plenty of rain such as 1997 and 2000, average berry weight did not exceed 3.3 grams. However, I am willing to say that it is very possible that we can hit an average berry weight of 3.5 grams (which could possibly be a record for the Vineyard Lab - I will have to check the long term data). There is also a question of seed number in relation to berry weight -- the greater the seed number in the berry, the bigger the berry (a true statement). Therefore, if we have a lot of 3 and 4 seeded berries in 2001, I would predict the potential for larger than average berry size. However, that is NOT the case in 2001. This berry count figure from the Vineyard lab shows that we have a larger proportion of single seeded berries and a smaller proportion of 2, 3, and 4 seeded berries in 2001 when compared to 2000. This is just another indication of a poor set in 2001.
| Berry Distribution (%) |  |
Here are some other observations from crop estimation activities. As stated in an earlier article, the crop is lower this year because of poor cluster and floret development and poor fruit set. Despite these 'across the board' events, it is nice to see there are some viticulture rules that are holding up. Potential crop increases with increasing vine size. As we move from one pound to three pound vines, the estimated crop increases because of greater clusters per shoot (or greater clusters per vine in the case of vines with the same node number). Excessively large vines (over 3 pounds on HRU at 9x8) had similar cluster numbers as the 2.5 to 3 pound vines but had lower fruit set (excessive vigor, shade, ?); therefore, the crop estimation on those vines decreased. We are predicting that the basics of optimum vine size and good bud selection (thanks to Ted and Mike) are going to give us a 3 to 4 ton per acre boost over vines of inadequate or excessive vine size.