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Crop Estimations - July 2026

By: Maria Smith, HCS-OSU   

The growing season soldiers on and so do tasks in the vineyard. With high heat and precipitation over the past month, the vines have continued their rapid growth. We’re at the point now where hedging and skirting are necessary (Figure 1). Nearing in at > 8 ft. of growth, the shoots are folding over and shading the canopy. In southern Ohio and some of our early ripening cultivars, veraison is here already and netting should be going on for bird protection.

Figure 1. Regent shoots > 8' in length shade the fruit zone. 13 July 2026

In Wooster, we are largely about 45-50 days following bloom and are taking crop estimations for the 2026 growing season. We expect veraison to begin for most cultivars in the coming days to weeks.

For grape growers and winemakers, crop estimation is important for several reasons:

  • Determining needs for fruit thinning and vine balance
  • Predicting yields for fruit sales
  • Estimating needs for tank space

The grape development process

Understanding the berry growth and ripening process can help understand how and when to take crop estimations.  

Grape berry ripening occurs in 3 distinct phases (Figures 2 and 3):

  1. Berry growth – cells are dividing after flower pollination, leading to rapid growth of the berry and seeds 
  2. Lag phase – the slow, stationary phase of berry growth 
  3. Berry expansion and ripening – this is the period when berry growth is driven by cell expansion through the accumulation of sugar and water 

While the pattern is consistent among all grapes, it is important to note that each cultivar varies in 1) when it reaches lag phase, and 2) how long lag phase will last.

Figure 2. Berry ripening curve - size and sugar accumulation. Figure from OSU Factsheet Crop Estimation of Grapes 

Figure 3. Berry development in Cabernet Franc at Hort 2, Wooster, OH on 24 June 2026 (Phase I - Pea-size), 13 July 2026 (Phase II - lag-phase), and August 2024 (Phase III - Veraison - note: we have yet to reach Cab Franc Veraison in 2026)

There are several methods and models for calculating crop estimation. The two most common methods include:

  1. The Lag-Phase Method: This method is conducted by weighing clusters during lag-phase and doubling the weight. This relies on the principal that berry size at lag-phase is approximately 50% of the final berry weight at harvest.

2026 Yield (tons per acre) = [2 * Cluster weight at lag-phase (2026) * # vines per acre (2026) * # number of clusters per vine (2026)] / 2000

  1. Harvest Cluster Weight Method: This method requires the historical average cluster weight at harvest, which is used to estimate yields based on the number of clusters per vine and the number of vines per acre.

2026 Yield (tons per acre) = [Ave. historical cluster weight at harvest * # vines per acre (2026) * # clusters per vine (2026)] / 2000

Both estimates require multiplying weight (2x lag phase cluster weight or historical cluster weight at harvest) by the actual number of vines per acre and an estimate of the number of clusters per vine counted following cluster thinning (note: if not thinning, cluster counts can be obtained anytime following shoot thinning between pre-bloom to lag-phase phenology).

There are many assumptions that are pulled into methods for crop load that influence the accuracy of measurements:

  • Lag phase timing is accurate for the target cultivar
  • Average cluster weight is reliable for the season in which estimates occur (i.e., it is a “normal” year for fruit set)
  • Final berry weight at harvest is consistent year-to-year (this gets more accurate with more years of historical data
  • Missing vines are accounted for in the vineyard block when multiplying the number of vines per acre
  • Sampling and representation are key: the higher the number of samples (vines and clusters) measured, the more accurate the estimates. OSU recommends a 100-cluster sample for estimated cluster weights per vineyard block. These and sampling for the number of clusters per vine should come from a minimum of 25 representative vines per acre across the block.

This year, we are choosing to weigh cluster samples at lag-phase (Figure 4) to obtain crop load estimates. This is because we have had ongoing issues related to fruit set in the past few seasons related to bloom-time weather conditions, 2,4-d drift injury affecting fruit set, and possible injury to inflorescences due to cold injury. This made using historical cluster weights unreliably over-estimate yields for our research vineyards in 2024 and 2025.

Figure 4. Cluster samples for estimating weights at lag-phase for crop estimations from Hort 2, Wooster, OH the week of July 13.

Highly cultivar-specific crop load calculators

If you have Concord, the folks at the Cornell Lake Erie Station have taken a lot of the guess work of lag-phase timing and crop estimation out for you. They have created a crop estimation calculator tool through the Efficient Vineyard website that aids in your crop estimation.  

Additional resources

There are several great resources available to help with your crop estimations. Below are ones that provide cultivar-specific information to lag-phase timing in addition to using GDD-based estimations for lag-phase and more general information on crop estimations.

 

Posted In: Viticulture
Tags: 2026 Season, Viticulture, Crop Estimation
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