Variable Thinning results
The practical results of chemical fruit thinning are highly variable because these are depending on many interacting factors. In a thinning strategy we distinguish between orchard factors that determine the need and susceptibility of an individual orchard for thinning, and the relative efficacy for a thinning application on a certain day, based on tree development and weather conditions.
To thin, or not to thin...
The decision to thin an orchard hard, little of not at all, has to be made by the grower and his consultant. This expert judgement is based on field information as: cultivar and age, previous years crop, number of flowers, growth and leaf quality, flowering conditions, initial fruit set, and previous experiences in this orchard.
When to thin
After the thinning strategy is decided, the DSS can help to find the best moments to apply the chosen thinning agents. The DSS implements our practical and scientific experience in fruit tinning, and applies this experience in real time using local weather data and weather forecast. The resulting ‘expected thinning effect ‘ is the best forecasts for thinning effects, but not a guarantee.
Flower Thinning (The blue lines)
From start of bloom, the model opens a new cohort of flowers every day. For each cohort the pollination and temperature dependent germ tube growth and fertilisation is followed. When the user decides enough flower cohorts have been successfully fertilized, he/she can start the ATS or lime sulfur applications to eliminate the later flowers.
Fruit Thinning (The red curve)
With the radio buttons at the top of the graph you can switch to see the expected thinning effect based on carbon balance, based on temperature in the days after application, or to see the expected combined effect.
The effect of fruit size
Early stage fruit growth is simulated based on air temperature. The competition between developing fruits and shoots is most critical when the average fruit diameter is 10 to 15 mm. The solid black line in the graph shows the expected fruit thinning efficacy based on fruit size only.
The effect of temperature
The temperature after application affects uptake and chemical activity of thinning materials, and the reaction of the plant.The yellow area in the lower graph shows the accumulated effective heat sum in the following days.The DSS corrects the expected thinning result for the heat sum in the days after application.
The effect of the carbon balance
Within the period of susceptible fruit size, trees are easier to thin when there is a shortage of carbohydrates. The DSS simulates photosynthesis and respiration (green and red in the lower graph), and corrects the fruit-size based curve for thinning efficacy for the availability of carbohydrates in the days before and after application of the thinning agent.
The combined effect of temperature and carbon balance
Depending on weather conditions carbon balance and temperature effects can ‘add-up’ and reinforce each other, or oppose and level out the expected thinning effect. In the current option ‘combined effect’ both factors have equal weight.
For thinning agents that interact with photosynthesis (metamitron , e.g. Bervis) the carbon balance in the days after application will have more impact than the temperature. For thinning agents with hormonal mode of action (e.g. 6BA, NAD, NAA, Ethephon), the temperature in the days post application tends to have more impact on the result.