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Growers increasingly recognize that grapes with greater sun exposure
develop more aroma and color and are less susceptible to powdery
mildew and botrytis. As a result, leaf removal has become a critically
important tool to optimize grape quality, and growers’ enhanced
interest has brought substantial technical development in leaf removal
equipment.
Leaf removers operate either by blowing compressed air with enough
force to sever the leaves or by sucking the leaves into the path
of a cutting tool. In Europe, leaf removers from Collard, Galvit,
and Siegwald (France) and Olmi (Italy) and others defoliate with
compressed air. The device is connected to a rotary power transmitter
on the tractor and is available for one-side, bilateral, or over-the-vine-row
operation. A large compressor delivers compressed air via flexible
hoses to leaf-removing head-pieces, which look like drums and are
positioned vertically next to the fruit zone.
Inside the drum, air is expressed in high-velocity streams through
rotary nozzles (outward curved air tubes). The nozzles rotate under
a cover plate pierced with narrow semicircular slots, which direct
the air toward the leaves that are to be removed. Work height can
be adjusted by rotating the slots.
The slots interrupt the airflow at short intervals, so that leaves
met by the air jet are not simply pressed to one side. The resulting
strong pulsations of air ideally tear a whole leaf off, however,
to a large extent, sections of leaf blades remain.
Compressed-air leaf removers are most suitable for early leaf removal,
between bloom and pea-size berry development. Some individual berries
will also be torn away, resulting in looser grape clusters and reduced
potential of bunch rot. During this period, there is little danger
that remaining berries will be damaged. A further advantage is cleaning
of the grape clusters, because the strong airflow removes debris.
However, in order to obtain the desired results, the airflow must
be accurately adjusted.
Leaf removers at Robert Mondavi Vineyards
Monterey Pacific Vineyard Company is operating Collard Raptor leaf
removers on approximately 1,800 acres near King City, CA, for Robert
Mondavi Vineyards. Mondavi bought the initial Collard Raptor leaf
remover in 2003, and it proved so successful that two more were
purchased in 2004. At the same time, Monterey Pacific purchased
its own Raptor leaf remover for use in other clients’ vineyards.
“We save roughly $100 per acre using the Raptor leaf remover
instead of hand labor,” reports vineyard manager Ben Eisner
at Monterey Pacific. “It costs about $25/acre to run the machines,
versus $130/acre for hand leaf-pulling.”
The Raptor mounts onto the company’s Braud over-the-row harvesters
and works one side of two vine rows at a time. Leaf removal is done
on the side of the canopy receiving morning sun, to expose clusters
to the air and sunlight and allow better pesticide application.
Leaves remain on the other side of the canopy to protect clusters
from afternoon sun and its attendant risk of sunburn.
Spacing in Mondavi King City-area vineyards is 8x5 or 8x6. The Braud
over-the-row chassis with two Collard leaf removers travels at a
speed of 1 ½ to 2 ½ miles per hour, covering an average of three
acres per hour, depending on terrain and foliage. The distance between
leaf remover and vine row is regulated with a guide rail.
The operator can make simple adjustments to take more or fewer leaves
as needed and reduce air pressure if too many leaves are coming
off or berries are endangered. One pass is usually sufficient to
remove the desired amount of leaves. Eisner or another Monterey
Pacific vineyard manager then walks the field to assess and, very
occasionally, might determine to take another pass or deleaf the
other side of a row.
Leaf removal procedures at Mondavi Central Coast vineyards were
determined by conferences between Mondavi vineyardists, winemakers,
and Monterey Pacific vineyard managers. Leaf removal usually begins
in May with Pinot Noir (at Mondavi’s 750-acre Bianchi Ranch
in Gonzales, Monterey County, CA). Leaf removal on Chardonnay, Merlot,
Syrah, and Cabernet Sauvignon occurs through June and into July
as needed in King City.
Introduction of mechanized leaf removal into the vineyard management
program worked well, and both Monterey Pacific and Mondavi are pleased
with the cost-effectiveness of the Collard machines. Eisner no longer
needs to hire, supervise, or adjust work crews constantly for hand
leaf removal, and he can leave a single operator with each machine
once it is mounted. The machines run day and night shifts during
the leaf removal season.
“The Raptors are bullet-proof,” says Eisner. “They’re
simple to operate and troubleshoot, and only take about half a day
to mount. They have plenty of power and adjustable hydraulic pressure
for terraced and hillside vineyards.”
The single downside to the mechanical leaf removal, notes Eisner,
is that it often needs to be done concurrently with spraying for
potential mildew; unfortunately, the sprayers mount onto the same
Braud harvesters as the Raptor leaf removers. Eisner finds himself
juggling machine time between spraying and leaf removal, but overall,
he is too happy with the benefits of mechanized leaf removal to
fuss about this new challenge.
Positive effects of leaf removal
Erika Winter, co-author of Winegrape
Berry Sensory Assessment in Australia, explains that better
sunlight exposure of the grapes and clusters leads to a warming
of the berries. This enhances the reduction of malic acid.
“These temperatures occur most often and are most prolonged
in the grape clusters in direct sunlight,” Winter explains.
“With higher temperatures, a slightly increased water evaporation
occurs, which causes an additional concentration of the berry contents.”
Good exposure of the grapes also promotes production of phenolic
substances in the berry skins. These include the red color materials,
or anthocyanins and tannins, and play a particular role in wine
character and color development of red varietals. A berry’s
aroma development is positively influenced by good sun exposure
of the grapes.
The main advantage of leaf removal is improved ventilation and exposure
leading to faster drying of clusters, which reduces mildew and botrytis,
Eisner reports. With less risk of rot, it may be possible to postpone
the harvest date, which may have a positive effect on grape maturity.
Timing of leaf removal is more crucial
than technique
Oswald Rage, a regional vineyard expert in the Rural Office for
Rheinhessen, Nahe, and Hunsrueck, Germany, and his German colleagues
studied the impact of leaf removal at different points in berry
development. First, they tried leaf removal between berries at pea
size and berry softening. These trials showed, however, that late
leaf removal can be unfavorable. In particular, serious sunburn
damage proved an increasingly large problem.
The Germans found that early leaf removal — between beginning
of flowering and pea-size berries — has clear advantages compared
to a later date. Early exposure of berries leads to a stronger layer
of wax and a thicker berry skin, which increase the resistance to
sunburn and botrytis.
A further previously unconsidered effect of leaf removal is improved
deposit of plant protection agents. As Eisner notes in his work
on the Mondavi King City vineyards, the amount of pesticide spray
landing on the grapes is clearly increased by first performing leaf
removal in the cluster zone.
The Germans discovered that, when defoliating only in each second
vine row, the spray values in the alternate (non-leaf removal) rows
were somewhat higher than when spraying every vine row without performing
leaf removal. They determined that with a leaf-pulled cluster zone,
they could reduce spraying to every other vine row if they wished,
and/or reduce the amount of pesticide used.
Fruit thinning with leaf removers
The Germans also tested the possibility of yield reduction by leaf
removers and decided that the idea offers some advantages. For the
purpose of thinning fruit, they found that compressed air devices
(such as the Collard leaf removers at Mondavi) were at a disadvantage
compared to suction devices used in Europe, which are fitted with
protective bars to prevent grapes from being sucked in. With adjustments
to the distance between the bars on a suction deleafer, they found
they could thin berry clusters while removing leaves.
However, they concluded that fruit thinning with a leaf remover
at the optimum time for leaf removal did not achieve the same berry
quality as manual fruit thinning at the beginning of veraison would
have done, and won’t be feasible without further study.
Like the Germans, Eisner isn’t ready to combine fruit thinning
and leaf removal. “We prefer to drop crop at veraison, so we
can determine uniformity better,” adds Eisner. “Combining
the two sounds a little scary to me, but if it were possible, you
could save another $50 to $100 per acre.”
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