Crop Load Thinning
“Fruit thinning is the single most important yet difficult management strategy that determines the annual profitability of apple orchards. Despite over 40 years of experience with chemical thinning, it remains an unpredictable part of apple production with large variations from year to year and within years due to weather”.
Crop load thinning is now recognized as vital to the effective management of apple orchards. Virtually all apple varieties have a tendency to over produce (set) fruit by up to 70%. Failing to appropriately thin will result in fruit that is small and discolored, with a lower market value while also damaging the trees from over bearing. It will also cause “biennial bearing”. This is when the tree only produces fruit every two years. Thinning is therefore vital to not only ensure a consistent size and quality for this year’s harvest, but also next year’s.
There are currently two methods for thinning crop load, chemical thinning or hand thinning. Hand thinning is a traditional, labor intensive method which involves physically removing the excess apples on the trees to ensure that each apple has the appropriate space to ensure optimum growth. During chemical thinning, a chemical is applied which stops the smallest buds on the tree from growing, only allowing the optimum amount for the load of the tree to survive. As can be seen from the table below, both of these methods have their advantages and disadvantages.
|No Thinning||Chemical Thinning||Hand Thinning|
|Benefits||Free||CheapCan be undertaken earlier in the process, therefore generating firmer and larger fruit||Easier to judge the optimal load|
|Problems||Reduction in size of fruitBiennial bearing||“More art than science”High chance of over/ under thinning||Expensive (labour intensive)Needs experienced supervision|
|Table 0‑1 Costs and Benefits of Different Crop Management Strategies|
While hand thinning is more accurate, it is extremely labor intensive, with costs of up to 5000 Euros per hectare. Chemical thinning costs on the other hand are between 500 and 1000 Euros. However, using chemical thinning requires decisions to be made on when, how much and what to apply. The scientific basis for these decisions is extremely weak and based on educated guesswork, resulting in both either under or over thinning.
“Lack of consistency is one of the major headaches for growers, who nowadays realize they cannot do without thinners but also fear over thinning.” HortWatch Website
Thinning is now almost universally practiced to a certain extent by all apple farmers, with evidence that chemical thinning can increase profit by up to 22% or 2 year profit by 89%. However, the relationship between fruit size, yield and profit is complicated, and results from the few studies that examine the impact thinning has on profits are inconsistent and inconclusive . It is accepted that thinning increases average fruit size, but also decreases the yield (and cost money). It is believed that the increase in fruit price is enough to compensate the loss of yield, but in reality there is a fine line between over and under thinning. This line is one that appears to be frequently crossed with some studies finding that over cropping reduces profits by over 20%, while under thinning can leave the farmer needing to hand thin which can add up to 350 labour hours per hectare. Therefore, the difference between successful cropping and over-cropping can be as much as 50% of the final profits. The fact that one study found the control of “under thinned” trees returned a net gain to the grower (compared with other appropriately thinned trees) of 33% shows that the understanding of what constitutes optimal thinning is considerably lacking.
Using mathematical models it is possible to map the appropriate level of cropping required to achieve the optimal return. However, few farmers are able to utilize these complicated tools. Furthermore, these models cannot say anything about the crucial aspects of what, how much and when the thinner should be applied. AppleGenie will be able to specifically answer these questions, ensuring the appropriate amount of thinner is applied at the correct time to ensure the optimal output of the right sized fruit to generate the maximum profit, considering both this year’s and future harvests, increasing profits, on average, by 25%.
 Robinson, T. (Department of Horticulture New York State Agricultural Experiment Station Cornell University) Advances in Apple Culture Worldwide
 Cook, R.L. 1985. Does supplemental hand thinning pay? Annu. Rpt. Michigan State Hort. Soc. 115:181–185.
 Gallasch, P T 1988 Chemical Thinning of Heavy Crops Proc. 6th Intl Citrus Congress p395-405 from Economics of Fruit Thinning, 2004.
 Silsby K J, T Robinson and F. Dellamano (1991) Empire Hand Thinning Study, Proc. New York State Hort. Soc, 136 175-186.
 Bergh, O, 1990, Proposed Regression Model for Calculating Optimum Crop Levels of Apple Trees, S. African Journal Plant and Soil, 7: 19-25.