The benefits of defoliation

How mechanical defoliation can increase desirable aromas in grapes and improve the first pick in apples.

Growers are already aware of the practical benefits of defoliation. Leaf removal and opening up the canopy ensures good spray coverage and increases airflow for better disease control, while making life easier for pickers come harvest time.

There are also a number of benefits to the quality of the fruit which, thanks to wider studies and independent farm trials, has data to back up the claims.

Research collected over four years from a range of vineyards growing Pinot noir in Oregon by Oregon State University proved that sunlight increases desirable aromas in grapes.

The study found up to 45% lower sunlight exposure in the clusters where no leaves were removed compared to the other defoliation treatments, 100% removal, 50% removal, and east-side cluster zone removal only.

While 100% defoliation was more beneficial than east-side only, there was no noticeable difference between the 50% or 100%.

The study also found that when the clusters were exposed to more sunlight, there was an increase in petunidin and malvidin, which could shift colours to more of a bluish, or a darker purple, and there was also an increase in beta-damascenone, which is an aromatic compound that gives Pinot noir its desirable blackberry aroma.

The research also looked at the effects of mechanical defoliation, compared to hand leaf removal. Data showed that mechanical methods could be used in the same way and were just as effective, showing the same results as hand thinning.

In the UK, where all-important hang time is often cut short by the pressure of bunch rot, early canopy management is also one of the best tools growers can use. Stripping leaves during flowering can encourage berries to remain small and less compact bunches are at lower risk of Botrytis.

For those looking for a defoliator suitable for their vineyard, the most common machines use what is known as a ‘suck and pluck’ system. These mechanical deleafers feature a fan which draw the leaves in towards two counter-rotating rollers which pluck them off the vine. A fan then chops the leaves and distributes the debris out of the front of the machine.

The key benefit of this style is that nothing is blown back into the canopy and so the machines can be used from flowering all the way through to harvest.

Depending on the size of their sites and budgets, growers can choose from the ERO or BMV defoliator heads. Both fit onto the manufacturer’s common frames that are also used for the ERO Elite and BMV E600A trimmers. ERO tend to suit larger growers looking for double-sided capabilities, while the BMV is a better fit for smaller-scale operations.

Trials carried out at Boxford (Suffolk) Farms also showed significant benefits to orchard defoliation when using the REDpulse Duo from Fruit-Tec.

Farm manager Peter Kemp ran several trials on the 110-hectare top fruit farm to compare fruit colour side-by-side.

The first assessment, on Gala apples, looked at the treated vs untreated rows 10 days after. The results showed an increase of 13% colour, from 32% to 45%.

A second assessment, conducted over 25 random trees a month after the REDpulse had been used and after the first pick, showed an overall average of 6 additional apples per tree were picked from the treated trees. The overall average colour was also 8% higher on the treated trees.

From a figures point of view, 75,882 more apples were picked in the first pick from the trees which had been defoliated with the REDpulse Duo. Using grading data from the previous year, the average weight of the Gala apples was 0.164kg, 12,445kg in total. Taking an approx. price of 65p per kg, this added up to £8,089.25 extra for the first pick.

“There was also a noticeable improvement in colouration on the second pick as well,” said Peter. “We were not expecting it to make quite as much difference as it did. I was very happy with the results.”