A New Tool for Apple Cropload Management - Cornell MaluSim Model for Determining Carbon Balance in Apple Trees

Posted: April 25, 2012

Dr. Alan Lakso, the Cornell pomologist who developed this model, explains that "the Cornell simplified apple carbon balance model estimates the general balance of tree carbohydrate supply versus demand of a 'standard tree', reflecting the effects of the input weather. It is not intended to apply to any specific orchard, thus the results should be used appropriately."
DailyCBal, Sup/DemBal, and TotalDemand for the complete season to date from green tip on March 14 through the projected April 27th

DailyCBal, Sup/DemBal, and TotalDemand for the complete season to date from green tip on March 14 through the projected April 27th

Dr. Rob Crassweller, Penn State Professor of Horticulture

The model is based upon years of research work by Dr. Alan Lakso. Environmental and physiological factors that are considered in the model include: leaf area development, light interception, daily canopy photosynthesis, respiration rate and dry matter partitioning within the tree.

This model assumes a constant load of 300 fruit per tree. The standard tree is a mature Empire tree at a spacing of 5 x 11 feet and trained to a spindle. The tree is well pruned and light is not limiting. It also assumes no stress such as drought, cold damage or nutrient stress. Obviously most orchards have had some type of cold stress this spring and this will affect how well the model portrays a tree’s response.

The model is based upon principles of carbon partitioning. If carbon supply is equal to total demand, then all organs grow at maximum rates. If the carbon supply is limiting, then the relative sink strength values (RSV) of the various tree organs are used to partition carbon. The competiveness of RSVs generally follows this trend from strongest to weakest: Shoots > Fruit > Roots = Tree Structure (wood).

As with all models it is not a precise replication but serves as one more general tool to help estimate the carbon or carbohydrate balance. When there is a carbohydrate deficiency trees will be more responsive to chemical thinners causing more fruit to abscise. When there is little or no deficit in carbohydrates the trees will be less responsive to the application of thinners and abscission of fruits will be less. You should take into account what your previous experience in your orchard with your cultivars has been.

Finally, the usefulness of the model will only be as good as the accuracy of the weather inputs. The predicted levels are also only as accurate as the predicted temperatures and sunlight levels. In our use of the model we are relying on data from SkyBit products created by Zedex, Inc.

Tabular values for Cornell MaluSim carbon balance model for Penn State FREC in Biglerville, PA through April 27th

Date DailyCBal SupDemBal TotalDemand
18-Apr 37.2            -4.6 41.8
19-Apr 59.5           -0.21 59.71
20-Apr 68.58 8.43 60.15
21-Apr 51.17         -22.56 73.73
22-Apr 35.9 5.69 30.21
23-Apr 36.52 18.23 18.29
24-Apr 86.57 52.89 33.68
25-Apr 92.02 48.4 43.62
26-Apr 25.86         -38.06 63.92
27-Apr 25.86 49.74 44.63

The table above shows the values for the Daily Carbon Balance (DailyCBal) Supply Demand Balance (Sup/DemBal), Total Carbon Demand (TotalDemand) since 4/18. The most important column is SupDemBal which shows either a positive or negative value. If the value is positive then there is an excess of carbon and trees will not be very responsive to chemical thinners. If the value is negative it indicates there is a deficiency of carbon and trees would be more responsive to chemical thinners. The values below the line in the table are projected values based on weather forecasts. As you can see the projected values for 4/25 is positive and 4/26 is negative, while for 4/27 it is positive. Remember when deciding on when to make thinner applications know the characteristics of the material you will be using.

The chart with this article graphically shows the DailyCBal, Sup/DemBal, and TotalDemand for the complete season to date from green tip on March 14 through the projected April 27th.

Again this is still a work in progress. We are still working out the bugs and hope to have more sites up from across the state in the near future. The sites we have chosen are dispersed across the state to hopefully represent a wide range of production areas. We would appreciate any feedback from you as to whether this was a useful tool helping you make decisions on when and at what rate to apply chemical thinners.

Contact Information

Robert Crassweller
  • Professor of Tree Fruit
Phone: 814-863-6163