H.L. Hutchinson Ltd recently hosted two workshops on the use of the apple and pear thinning product Brevis, one in Ledbury, Herefordshire and the other at their Canterbury, Kent depot.
Rob Saunders, horticultural project manager at H.L.Hutchinson Ltd, by way of introducing the workshop, said: "You could argue that for apple growers thinning has now become the most difficult and the most important decision of the year. This is particularly true of varieties like Gala, bearing in mind the very specific size ranges now demanded by the multiple retailers."
Rob pointed out that there have been various chemical thinning strategies in the past but reliability has always been a problem. Adama has been making strenuous efforts in the last few years with gobal research on the use of their product Brevis, including European research and development trials, to work up a model for growers to follow.
Ton Besseling is Adama's Global Project Manager for Brevis and, as the son of a Dutch fruit grower and with a brother still growing pears, he is well qualified to understand growers' dilemma. He said that his mission at the workshops was to explain the product, share experiences from other countries and describe the difficulties of thinning. Every year is different and, like us, the Netherlands was two weeks ahead of a normal year by the end of March. Everyone hopes to avoid a severe late frost like the one in 2017 which meant that Ton's trials lost a year, but he did get good results in 2018. He pointed out that, for the Netherlands, average temperatures, rainfall and radiation (a particularly important factor for thinning with Brevis) are similar to ours in the UK, so trials results in Belgium and Holland are relevant for us.
How does Brevis work?
So how can Brevis influence the thinning process? Many varieties set too many fruits; Brevis limits the radiation used by the tree, so reduces the production of sugars; this could be described as mimicking a 'shading' effect on the tree; less sugar leads to an increase in natural fruitlet drop. We need to understand the balance of sugars within trees. Unfortunately, we can't measure this, but it is true that history plays a part as, if the tree carried a heavy load last year, it will be easier to thin. There is optimal sugar production on sunny days followed by cold nights leading to high sugar reserves. In these circumstances thinning is more difficult to achieve. The consumption of sugars is subject to competition between king fruits and lateral fruits and shoots. With the increasing importance of thinning, combined with the increasing cost and scarcity of skilled labour to hand-thin since the loss of Carbaryl in most countries, Brevis offers a new approach. It is not a hormone, it's a photosynthesis inhibitor with a window of efficacy between 6mm and 20mm fruitlet diameter.
Much has been learnt since Brevis became available in 2015 and there have been some label changes since then. Originally growers were advised to give a seven-day interval before and after applications of other products with oily formulations, such as fungicides like Fontelis. But trials have shown that Brevis can be used in programmes with oily formulations, so the label now reads that a three-day interval is sufficient. Several mixtures have been tested with no negative effects, but Ton says, "we prefer to separate fruit-thinning from crop protection to avoid any interaction". There has also been a slight change to the timing of application to a window between 6mm fruitlet size up to 20mm. Ton says it is best to start your first application at 10mm to 12mm and keep the option of a second application at 16mm to 18mm five days later. Brevis can be used after flower thinners and Ton has had good results with ATS, which is useful to remove king fruits. It can also be used on just part of the tree, normally the upper part, as it is possible to over-thin the lower, more shaded, parts of trees, and more difficult to hand-thin the tops.
Adequate, well-maintained spray equipment is crucial for the success of all chemical treatments, but this is especially so for Brevis. Good coverage is vital and, in some trials, very high volumes of water of 1000-1,500 litres/ha were used. Ton admits that growers will use less and he recommends 400 litres/ha in Dutch and UK conditions where there are smaller trees and good humidity. Some trials in the Netherlands with 250-300 /ha did get good results. Wetters or adjuvants are not necessary, water is a good carrier if evenly distributed over the tree.
Radiation is an important factor related to the efficacy of Brevis and a shading trial proved this very neatly. Shading trees with black netting for five days was compared with a Brevis treatment alone or Brevis plus shading. The shading produced a 40% thinning efficacy whilst the Brevis was increased from 18% to 58% with the shading. Ton advises that there will be a stronger thinning effect with Brevis if cloudy dull weather follows the application. Another important factor is night temperature and there will be a stronger effect if there are higher night temperatures (above 10C to 12C) before or after application. High humidity also promotes the uptake of Brevis, so spraying should be done in the morning or evening when humidity is highest.
The BreviSmart model
Ton introduced the BreviSmart tool that will support decision-making. Thinning is a complex process, with the model already predicting 60-70% reliability. Since 2013, Adama has been sponsoring a group of ten researchers around Europe to develop BreviSmart. Rob Saunders is a member as the UK representative on the Brevismart development group and has been attending for the last couple of years. He says, "The group is a brilliantly collaborative gathering that meets twice per year, somewhere in Europe. It is mainly made up of researchers, but I provide the 'voice of the agronomist' and the UK perspective in the discussions". BreviSmart® is a web-based tool that can be used on a computer, tablet or smartphone and uses fruit size and local weather forecasts from the 'The Weather Company' to help decision-making, allowing advisers to give growers 'best fit' application dates.One aspect of applying thinning products that is often missed is to leave a few trees untreated in order to assess the effectiveness of your treatment. Ton recommends using Brevis on older trees from five to six years old for apples and seven to eight years old for pears. He also warns to avoid drift onto stone fruit as Brevis is not useful for them. However, he promises another compound for thinning stone fruit that is in development.