To target high quality fruit, strategic cropload management practices are currently being investigated in designed field experiments at DEDJTR, Tatura, in the stonefruit experimental field laboratory. Manipulating fruit number per tree, offers the ability to regulate available assimulate, to maximize fruit size and fruit quality. Removal of fruit may involve a combination of orchard techniques. They include pruning, blossom thinning, and hand fruitlet thinning practices. Typically commercial peach and nectarine orchards set a target for a number of approximately 1 fruit per 10 centimetres of fruiting lateral.
At Tatura, in the experiment orchard cropload fruiting level treatment treatments being investigated are, high, medium and low cropload targets. The high treatment is minimally thinned fruit to levels to maximize competition between the fruit and available assimulate. The medium fruiting level is a moderately thin fruit to minimize competition between fruit and available assimulate, and a low thinning level treatment is heavily thinned fruit to eliminate competition between fruit and available assimulate. The high cropload treatment is minimal fruit removal, and were we only removed from clusters that are thinned. The medium cropload treatment mimics typical commercial practice where we target fruit number approximately one fruit per 10 and that's per fruiting lateral. Low treatment has most fruit removed from the tree. The Tree architectures being investigated at Tatura in the cropload management experiments include vase configuration trees, vertical Leader trees and Tatura trellis trained trees. The crops being studied include nectarine, peach, apricot and plum.
Results to date show cropping levels have marked impacts on yield, fruit size and in most cases fruit sweetness, fruit maturity and fruit firmness.
The results from the 2016-17 season for nectarine Rose Bright, early season cultivar, under different cropload regimes, can be seen in those two data graphs. For fruit size we have a range of histograms for high, medium and low cropload treatments. For fruit sweetness, high, low and medium cropload treatments. We can see the distributions for that. Going back to fruit size, we had a major shift in the size of our fruit, on the high, low and medium cropload treatments where we can see the red line here, the low treatment, for example, had overall larger fruit and a high portion of larger fruit. Conversely, the high cropload treatment, produced many small fruit. When we look at the profiles of fruits sweetness. we get again, a shift to the right under less fruit per tree, so the low cropload treatment having sweeter fruit, overall.
The data for peach August Flame, a mid-season cultivar, similar sort of trends under high, low and medium cropload. We've also got two canopy configurations, a vertical leader system and a Tatura trellis system. So when we look at fruit size, under the high, low and medium, we're getting a major shift in our fruit size profiles when we have a high crop low treatment compared to the low and medium treatments. There's not as much distinguishing features in the fruit sweetness profiles. That's with the vertical leader. Similar sort of trends in the Tatura Trellis under high, low and medium cropload where the high cropload had smaller fruit and not as sweet. Another example of some data we have on nectarine Autumn Bright, another mid-season variety, under both vertical leader and Tatura trellis. Again we're getting shifts in both fruit size and fruit sweetness profiles with their cropload management for both Tatura trellis and vertical leader systems. Last season data for plum under 2 canopies, we had three standing vase trees and a Tatura Trellis canopy configuration. For the vase, fruit size differences with less distinguished, and similarly fruit sweetness was very similar, under the three regimes cropload but under the Tatura trellis however, we definitely got major shifts in fruit size profiles when we went from high fruit number per tree to the medium at low levels. And it looks like we're getting an improvement in our sweetness percentages as well.
Similar canopy configurations under apricot, last season we had a vase system compared to a Tatura trellis system under high and median croploads. Again, similar story, we have a shift in fruit size profile as we have less fruit per tree, but not much change in fruit sweetness and that occurred also in Tatura trellis as well as the vase.
Overall fruit thinning and tree management strategies for improved fruit quality include, adjusting cropload to maximise fruit size and fruit sweetness. When economically viable i.e. if financial returns are higher for better quality fruit. Early thinning when fruit diameters are less than 15 millimetres in size, is a good practice to maximize cell number in the fruit flesh and thus final fruit size at harvest.
To target fruit quality outcomes in peach and nectarine, our data to date suggests setting a cropping level of one fruit per 12 to 15 centimetres fruiting lateral.
In canopies that have poor light distribution in the lower parts of the tree canopy, we suggest maximizing fruit numbers in higher part of the canopy, reduce the number at the base of the tree to improve the uniformity in fruit quality and size.