The “Crop Estimation Chart” referred to in these steps can be found under the Crop Estimation Table tab.
Bloom date and days after bloom:
This system is based on bloom date, and in order to be accurate you need to know when your grapes were at 50% bloom. The 50 year average date for 50% bloom is June 14th. Count off starting at your bloom date and accrue the respective days-after-bloom (DAB). On the chart the DAB is found in the shaded “Time of Season” and not to be confused with “% of Final Berry Weight” directly below.
Like bloom date, you need to know your vine spacing. Row spacing determines the length of a row that will equal 1/100th of an acre. The wider the row, the shorter the sampling length. For example, sampling a block with a 10’ row you will need to clean pick 45.9 feet. If your rows are at 7.5’ spacing, you need to clean pick 58.1 feet. If you have 9-foot row spacing and your panels are at 24 feet then this should be easy. However, it is best to determine your row spacing and cut a length of rope to guide your sampling lengths rather than rely on post lengths that have been changed out over the years.
Once the row spacing and sample distance is calculated, clean pick and weigh the samples. The more samples you take, the better your prediction will be. It also helps to take samples from areas of known variation across the vineyard. For example, take 2-3 samples from high vigor, medium vigor, and low vigor sections of the vineyard and apply your predictions appropriately to those sections. If you are using a harvester to clean pick panels walk behind afterwards to assess how many grapes are still on the vine/or that are on the ground.
Using the Chart:
Once you have the sample, the chart does the rest of the work for you. Follow the corresponding DAB down and the respective weight over and you have the estimated tons/acre at harvest. For example, let’s say it’s July 25th or 40 DAB (bloom on June 15th) and the average from 4 samples weighs 100 pounds. I would have an estimated 8.3 tons/acre potential crop.
Things to keep in mind:
If you have an accurate bloom date for your vineyard, follow the crop estimation chart to predict final harvest weight. If you’re not and you are using the actual berry weight samples to come up with your multiplication factor, be reasonable in what you think your final berry weight will be. Some vineyards tend to have smaller average weights and some tend to be larger – and you should be starting to get an idea where your vineyard fits. Be reasonable – it is unlikely (highly unlikely) that your Concord vineyard will average 4.0g berries at harvest even if your 30 DAB weight was 2.0 g.
Getting it right is important. Underestimating crop potential can lead to delayed harvest waiting for the grape to ripen and the BRIX to rise. Overestimating a crop load may result in unwanted thinning or unnecessary expensive chemicals being used to care for a crop that is not there.
Having an accurate crop estimation can help you make many cultural practice decisions thought the rest of the season. The following is a break-down of the process.
Crop estimating at 30 DAB for ‘Concords’ is common for most growers. When the berries are at 50% of the final berry weight (like the example shown above) all you needed to do for final estimation is shift the decimal point over one place. However, the estimation table will work throughout the season. One thing to keep in mind when using the chart is to double check you are using time of season (DAB) in the shaded area to match up the column below.