When the carbon balance or the difference between the carbon production through photosynthesis and the carbon consumption through respiration is negative for several days, the tree will start using its carbon reserves, experience stress and drop fruits. Radiation will determine the photosynthesis rate, which can be negatively influenced by a photosynthesis inhibitor like metamitron (Brevis). In general, there is a high demand for carbon in the period prior to June drop depending on the number of flower buds and the strong competition between shoot and fruit growth. Night temperature determines the respiration, while plant growth regulators (e.g. 6-BA) can affect both respiration and the competition between shoot and fruit growth. The Malusim carbon balance model uses climate data before and after (weather forecast data) the time of application of a chemical thinning agent to predict the effect of the thinning. Other models are under evaluation at pcfruit, too. Using night temperature and radiation data the effect of Brevis thinning at different time points or fruit sizes could be explained.
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