Apple growers are looking for ways of reducing or eliminating expensive hand thinning so that they can produce the right balance of crop load and fruit size more cost-effectively. There are suitable products such as 6-benzyladenine that will increase the number of single fruits and so thin apples chemically, but they need to be applied precisely within the correct conditions of application.Stewart Woodhead, Technical Manager for Interfarm UK explains that the active ingredient in MaxCel, 6-benzyladenine, is a cytokinin-type plant growth regulator found in nature. “This group of plant hormones affects a number of processes in plants including apical dominance, axillary bud growth, cell division and growth and also leaf senescence. MaxCel selectively thins developing apples. Fruit size is also increased due to reduced competition for nutrients and due to an enhanced rate of cell division and growth, resulting in increased marketable yields.”“Timing of MaxCel is crucial to its efficacy. The label says that it should be applied when the king fruitlet has a diameter of 7-15 mm, with the optimum range being 10-12 mm in size. But it is the temperature that is key to its success. MaxCel should be applied at the start of a warming period when the maximum daily temperatures for the 2-3 days following application are expected to be 15-18° C. It should not be applied when temperatures are below 15° C,” says Stewart.MaxCel is recommended on all varieties of apples at dose rates of 3.75 to 7.5 litres/ha. The dose rate varies on the variety to be thinned and the state of the crop. Formulated as a soluble concentrate, it is ready for the grower to use and is unique in requiring no additional adjuvants. One application can be made per year and the latest time of application is when the king fruitlet is 15mm. It is fully compatible with IPM programmes.It is also important to ensure adequate coverage of fruit and foliage but without excessive run-off. To achieve this, water volumes should be adjusted according to tree size and spacing. Water volumes of 1000 litres/ha in air assisted sprayers will give adequate coverage of fruitlets and foliage.“Achieving premium size grading is important for marketing quality produce and enhancing fruit size alone can more than pay for the treatment. The use of MaxCel can increase growers’ returns by reducing hand-thinning in apples, improving fruit size and quality. It also promotes strong return blooms for the following year, so it is not just the one benefit of fruit thinning in one year,” says Stewart Woodhead.