# Technologies for Forecasting Tree Fruit Load and Harvest Timing--From Ground, Sky and Time
## 2 Measurement of Fruit Number
### Manual Fruit Count
#### 2.3.3 Examples
This method involves six steps: (i) an estimation of the bearing surface of trees, (ii) the selection of sample trees, (iii) a count of fruit in a frame of known dimensions (e.g., 1 m\({}^{3}\)) placed into the canopy of each sample tree, (iv) the measurement of fruit size and (v) the measurement of fruit retention rate. [PERSON] and [PERSON] [29] recommended a count of 20 frames per hectare, noting that for more accurate and better representation, more units could be sampled. [PERSON] [30] recommends counts of fruit in a frame of 60 trees per citrus block, with sampling of at least two sides of the tree. The estimated time for this procedure was 60 min per block. A technique for forecast of grape yields was documented by [PERSON] et al. [31]. The method involves: (i) the definition of patches, (ii) the counting of bunches within the patch, (iii) the counting of berries in sampled bunches, and (iv) the weighing of sampled bunches. Patches are groups of vines similar in cultivar, spacing and vine structure, which are essentially an orchard in the context of this manuscript. Bunch counting may be performed on a trellis segment basis, or by use of a counting frame. Berry counting can begin after the fruit set. An initial assessment of 60 bunches per patch is recommended, with assessment of more bunches to meet specific accuracy requirements. An RS strategy of selecting plants before entering the orchard is recommended, with a stratified RS (strata based on equal number of plants) for irregular-shaped blocks to prevent clumping of samples. Bunches can be sampled after veraison for the assessment of weight, with a projected growth curve and an estimation of time to maturation used to estimate final yield. The US Department of Agriculture (USDA) undertakes manual fruit load estimates for an industry-wide harvest forecast in several crops. Almond forecasts based on crop sampling two months before harvest have had an average error rate since 2001 of 7.3%, with the worst annual error being 13.8%, while the average error rate over 34 years of the hazelnut crop forecasts was reported to be 8.1% [32]. The hazelnut forecast, for example, is based on a survey of 180 randomly selected orchards, with two randomly selected trees per orchard. Each year, 50% of trees are retained from the previous year. Two primary scaffold branches per tree are marked for sampling before nut set. Four months later, all nuts from the sample scaffold branches are picked from the tree and sorted into eight size groups, and for defects. The total industry yield is estimated as a product of the nuts picked per tree, average nut size, the dry weight per 'good' nut and the number of trees in production. Examples of commercial yield estimations using the SUR sampling method have been provided by [PERSON] et al. [33] and [PERSON] [34]. Surveys were carried out by two-person teams, with one person counting fruit on small portions of the trees and taking subsamples of fruit for the measurement of mass and other properties, the other person guiding the sampling and recording counts and masses using the app [25]. Any plants or branches selected by the algorithm that did not bear fruit were ignored (the next fruit bearing unit selected instead) to increase efficiency. For sweet cherry orchards with areas of 2 ha, less than 3 h were required to obtain projections to the date of harvest with absolute errors of 0.5-10%. Six hours were required for a 6.7 ha orchard, and the resulting estimation error compared to packhouse records was only 2%. A 50 ha vineyard was sampled over two seasons. In the first season, the survey of bunch counts and a subsample for bunch weights took 9 h to complete, for an overall estimation error of 0.4% relative to the harvested weight. The following season, a smaller sample, requiring 6 h, provided an estimation of yield with a \(-3.3\%\) error. In comparison, the winery's estimation of bunch counts for the same blocks required three days of effort by a five-person crew, equivalent to 16 days by a two-person team. Similarly, [PERSON] et al.