The range of fruit sizes at harvest can now be predicted well before harvest with the new fruit growth model. The current model makes predictions for Gala, Red Delicious, and Cripps Pink.
Fruit growth is correlated with temperature, just like insect development. Fruit growth progresses as degree-days (DD) are being accumulated and it ends when a certain total number of degree-days have been reached. This degree-day total differs between the various cultivars, as they mature at different times of the season.
The degree-day sum on any given day tells us at what percent of the full size the fruit currently is. For example, at 1440 DD, the fruit has reached 50% of its final size. After this point, final fruit sizes can we estimated with increasing accuracy. Just take a sample of apples and measure their current size. Then multiply the measured fruit sizes with a size factor given in the DAS output for the day you took the sample to get the estimated final fruit size distribution.
The model information helps to predict when full fruit size is reached and what the range of the final fruit size will be. This in turn helps to plan harvest timings and needs. Knowing the speed of fruit growth also provides information about how fast pesticide residues on fruit may dilute. In addition, this model predicts when fruit may be vulnerable to certain insects that only attack fruit of a certain size, as the Western flower thrips does, for example.
The development of these models was based on extensive data sets collected by the Washington Tree Fruit Research Commission.
To see the model output for new models, edit your station in your DAS account settings and add any model to that station. As always, your feedback and comments are most welcome.
The DAS Team