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Cornell MaluSim Carbon Balance Model Update for Penn State FREC

Posted: April 30, 2012

The Cornell MaluSim Model can be used to assess potential thinning response of apple trees. 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.

The usefulness of the model will only be as good as the accuracy of the weather inputs. The predicted levels are only as accurate as the predicted temperatures and sunlight levels.

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.

Based on conditions at the Penn State Fruit Research and Extension Center the model predicts a carbohydrate deficit over the next several days.