Practical Winery
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This article is from the March/April 2005 issue of Practical Winery & Vineyard Magazine. Order current or back issues here.


March/April 2005

BY Tina Vierra

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.”