Practical Winery
58-D Paul Drive, San Rafael, CA 94903-2054
phone:415/479-5819 · fax:415/492-9325

March/April 2001

Decreased spraying improves quality, nature, bottom line

Bill Petrovic & David Rosenthal

The physical size and length of vine rows at the San Bernabé Vineyard (King City, CA) mandate that the majority of the spraying is done at low (30 gallons per acre) volume. In many blocks of the almost 7,800-acre ranch, one complete tractor-trip covers approximately 10 acres with a 300-gal. tank or 16 acres with a 500-gal. tank.

Combined with hilly terrain, which limits the total carrying capacity of a spray rig, the need for lower volume is clear. Secondly, with so many acres to spray in a timely manner, fill-time is down time, which decreases efficiency and acres covered per day.

Afternoon winds which cause evening cooling at San Bernabé also limit the usable spray hours in a day, mandating a 3 a.m. start time for the spray crew. The sprayer must generate enough velocity to overcome the wind. However when the wind velocity exceeds five mph, the spray program is required to stop for the day.

Trellis systems, row spacing, and grape variety (separately and in combination) determine the equipment, materials used, and application frequency. Chardonnay, which has the highest risk for powdery mildew, may receive five spray applications of sterol inhibitors and wettable sulfur per year, plus eight sulfur dustings.

Cabernet Sauvignon may need only two fungal sprays and eight sulfur dustings. Chardonnay trellised on Smart-Dyson or conventional bilateral cordon can be done with span sprayers, electrostatic sprayers, or air-blast sprayers at low to moderate (30 gallons per acre) volume. Chardonnay on a split canopy is better served with an air-blast sprayer, which can penetrate under the canopy with an upward diagonal pattern.

Material and labeling restrictions are other factors determining the type of sprayer needed. Certain materials have restricted use to 50 or more gallons of spray solution per acre. An electrostatic sprayer cannot effectively charge material above 35 gallons per acre, and span sprayers at 50 or above have to run at a reduced speed to generate the volume of material required per acre. When using certain products demanding higher (above 50 gallons per acre) volumes, the air-blast sprayer is the answer.

Spraying equipment
The foundation of a spray program is the material delivery system. Due to its canal and well system, San Bernabé has unlimited water sources, but we still have to deliver water to the mix tanks. Four thousand-gallon water trucks deliver to a series of mix tanks, which in turn pump into the individual spray rigs. Three types of sprayers — spraying three distinct spray mixtures in any combination of trellis and variety — are typical.

San Bernabé has been experimenting with electrostatic sprayers for several years, building its own tanks and boom systems and using commercial manufacturers’ spray heads. Electrostatic is an excellent concept, and the ultra-low (10 to 12 gallons per acre) volume allows the potential for increased efficiency due to less fill-time. Due to its low volume, certain materials cannot be used (Rovral, Procure, and Rally), and on high heat (above 90F) days, the material evaporates before it hits the target.

Another electrostatic spray rig can deliver up to 35 gallons per acre of fully-charged material, which seems to fit San Bernabé conditions well. This spray rig was redesigned to fit San Bernabe’s needs by the equipment staff at Coastal Valley (the management company which farms San Bernabé).

Electrostatic spray rigs encapsulate the target with material as they are designed to do if there is nothing behind the intended target. Early in the season when there is little leaf mass, the process works effectively. However, if there is a leaf on the backside of a cluster, the material will coat the leaf and not the backside of the cluster. On high fungal-sensitive varieties such as Chardonnay, leaf-pulling increases the efficiency of all sprayers as the season progresses.

The span sprayer has been the workhorse for many years, but the horse is getting lame. Span sprayers use air as the carrier spraying 30 gallons per acre efficiently. The main problem is the heart of the system, which is a hydraulically-driven fan. The fans have to be continually rebuilt since they turn at high rpm and leak oil when a seal fails. This factor, combined with low visibility at night leads to hydraulic oil burn on the canopy and grapes. The span sprayers will be phased out in the near future at San Bernabé (three to five years).

Air blast sprayers with towers are the most versatile spray rigs, since they can be used efficiently at both low (30 gallons per acre) and high (200 gallons per acre) spray volumes. They are the choice for dense canopies and materials (Rovral, Procure, and Rally) requiring high volumes.

In 2000, we tested a four-row sprayer mounted on a custom over-row tractor. This is a sprayer, which works best when delivering 25 to 30 gallons per acre. Due to the sprayer covering four rows, it has to be low volume or it would not complete a pass in the longer (one-mile long) rows in the vineyard. The sprayer has a boom which levels to the terrain — opposite of how the machine levels.

Methodology and Philosophy
San Bernabé is unique in that the staff determines when and what to spray. There is an in-house pest control agent (PCA) and an in-house lab to perform field checks. There is no commercial application of spray material or field-checking by an outside vendor. The lab uses three or four ranch-trained personnel, full-time employees who oversee seasonal crews during pruning to check the fields on a weekly basis. The crew does excellent, concise work, which allows real-time response to problems and the ability to postpone sprays.

Having accurate data from the lab and the use of an ADCON system (a weather system that calculates a severity index for powdery mildew) allows us to extend time intervals between sprays.

The only commercial influence in the disease control spectrum is the use of an airplane applicator for sulfur dusting. Applying sulfur via airplane allows quick response to wet weather rather than waiting for the ground to dry to allow tractors in. Airplanes, of course, can also cover many acres per day. Sulfur is a wonderful preventative treatment for mildew, and it allows longer intervals between foliar sprays.

San Bernabé is one of the founding members of the Central Coast Vineyard Team, a group of growers and wineries that is looking at an environmentally balanced approach to farming and chemical use. We have been using permanent cover crops (Blando brome, zorro fescue, natural/native grasses) to promote beneficial insects, and using target-specific conventional chemistry and effective organic materials in our spray programs.

Currently, we are using a myriad of organic compounds (Bts, soaps, and oils) and have selected Bts (Bacillus thurengiensis), all of which have efficacy in our program. The one drawback of most organic material is that it has to be applied within such a narrow time band, making it impractical except on small (less than 500 acres) acreage.

Not only do we spray only when positively needed, but we also alternate our materials so that resistance to a specific material is not established.

Because of its size, varying trellis systems, and spectrum of grape varieties, San Bernabé cannot depend on one type of sprayer. The trend at San Bernabé will be to stay on the lower end of volumes, approximately 30 gallons per acre, since that is the level where spray efficiency and acre-coverage are most effective. We must have the option to have efficiency on both the higher and lower volume ends for any situation beyond the norm. Having a combination of air-blast and electrostatic machinery enables us to accomplish that objective.