A.N. Lakso, T.L. Robinson
Despite decades of thinning field trials, chemical thinning remains one of the more unpredictable parts of apple production with large variations within years and from year to year. Many factors affect apple thinning response including chemical dose, chemical uptake, and fruitlet sensitivity to chemical induced abscission. A significant amount of variability appears to be related to the availability of carbohydrates to support fruit development that integrates the environment and the crop demands at the time of thinning. For decision support, we simulate these interactions with the MaluSim carbon balance model using a reference dwarf tree but local environmental inputs (daily max and min temperatures and total radiation), analogous to Evapotranspiration ETo calculations using a reference crop. Model simulations from several years showed that there are often periods of particularly negative or positive carbon supply:demand balance which were associated with severe thinning or mild thinning (poor carbon balance leading to excessive drop or thinning). Model simulations have also helped explain strong abscission responses to unusual weather patterns. The simulations are interpreted as providing a baseline of tree sensitivity to chemical thinners. We have used these simulations with the MaluSim model and local weather from several regions of New York State to predict thinning response with good but not perfect success. This information is being provided to growers to help predict thinning efficacy of sprays and thereby adjust concentrations of chemicals to better achieve the optimum crop load.
Lakso, A.N. and Robinson, T.L. (2015). DECISION SUPPORT FOR APPLE THINNING BASED ON CARBON BALANCE MODELING. Acta Hortic. 1068, 235-242
DOI: 10.17660/ActaHortic.2015.1068.29
Malus × domestica, simulation model, carbon balance, chemical thinning, carbohydrate, temperature, light intensity

Acta Horticulturae