# Technologies for Forecasting Tree Fruit Load and Harvest Timing--From Ground, Sky and Time
## 2 Measurement of Fruit Number  
### Benchmarking  
#### 2.1.1 Reference Estimates  
Any analytical procedure involving the comparison of one method to a'reference' method should include an assessment of the error in the reference method. Methods for fruit load estimation need to benchmark to a reference measurement. Where method validation involves a small number of sample trees in the orchard, the reference value is typically a human count of fruit on-tree, or a human count of fruit harvested from the tree. Such estimates are not error free.  
To benchmark a fruit load prediction at a whole orchard level, the reference estimate is commonly estimated from the fruit packout report. However, [PERSON] and [PERSON] [10] cautioned that self-reported crop data were not accurate enough for predictive model training for a small holder grain production system, even when the use of the data was explained to the contributors. Similar issues hold for the tree fruit production system. Packhouse record keeping is often lacking, particularly if fruit from several producers or multiple orchards per farm are processed in the same shift, or if orchards are harvested over several dates. Further, harvesting operations may move across several orchards at a time, such that tree crop packout data may not be organized to easily provide orchard level data. The increasing adoption of field bin identification systems and farm data management systems is improving this situation.  
Packout fruit numbers can be estimated from records of the number of trays of a given fruit number per tray. While rejected fruit are not packed, a weight is generally taken. The fruit number can then be estimated using an average fruit weight, although the use of the average weight of packed fruit will typically result in an underestimation of the rejected fruit number, as a low fruit weight is a criterion for rejection.  
The packout count can be expected to be less than the orchard fruit load as fruit drop may occur between the time of load estimation and harvest as a result of extreme climatic events, disease or abortion. Further, fruit may be left on-tree either accidentally or deliberately as harvesters avoid under or over mature and defect fruit, and low yielding canopy areas if paid on a piece rate. In the authors' experience, counts of fruit left in orchard after harvest range from \(<\)1 to \(>\)50%, e.g., between a'strip pick' in which all fruit is harvested, with sorting in the packhouse, and a poor management of harvest resourcing. Harvest efficiency can be added into a forecasting model., e.g., the Australian Grape Forecaster tool ([[https://www.fairport.com.au/en/features-en/grape-foreaster](https://www.fairport.com.au/en/features-en/grape-foreaster)]([https://www.fairport.com.au/en/features-en/grape-foreaster](https://www.fairport.com.au/en/features-en/grape-foreaster)); accessed on 19 April 2021) applies a set of factors for different harvest conditions, e.g., 90% for very efficient machine harvest [11].  
Few published studies on tree fruit estimation present data on the error of the reference technique. The presentation of such data is recommended for future reports.