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April 2014 Issue of Wines & Vines

Why 'per acre' spray dose calibration no longer applies

by Larry Whitted
practical winery vineyard

Recommendations for pesticide application have been made on a “per acre” basis, and growers have applied them on a per-acre basis. During my 34-year career as a pest control adviser I have recommended pesticide applications on a per-acre basis.

At the annual Farm Safety Day, in Lodi, Calif., I teach a class about how to calibrate spray rigs on a per-acre basis. Astute growers have observed that this practice does not really make sense, and I have readily agreed with them. In fact, entire countries, having realized this, have abandoned the practice.

On Target sprayer
Photo supplied by On Target spray systems.

I think the time has come for us to take a closer look at the use of per-acre spray calibration.

There are 43,560 square feet in an acre. If we were spraying alfalfa then we would spray all 43,560 square feet, but we are not. We are spraying vine rows, and the amount of vine row in one acre depends on the space between the vine rows. If a vineyard is planted with 12-foot-wide tractor rows, then 1 acre consists of 3,630 linear feet of vine row per acre. If a vineyard is planted with 9-foot-wide tractor rows, 1 acre consists of 4,840 linear feet of vine row per acre.

A highly effective and fairly expensive miticide applied by some Lodi growers is Acramite 50WS. The label calls for a dose of 0.75 to 1 pound per acre. If you apply 0.75 pounds per acre in a vineyard with 12 feet between vine rows, then you are applying 0.75 pounds per 3,630 linear feet of vine row. Another way to say this is that you are applying 3.3 ounces of Acramite per 1,000 feet of vine row.

    Welcome to the Coffee Shop


    This article was originally written for the Lodi Winegrape Commission’s Coffee Shop blog, a viticulture research and practice information resource available at

    One of the Lodi Winegrape Commission’s (LWC) chief objectives is to provide Lodi (Crush District 11) winegrowers with opportunities to learn about sustainable winegrowing. In an effort to continue our tradition of innovate extension, the LWC has launched a new grower-oriented website (, which strives to be a one-stop shop for practical winegrowing information.

    Among the website’s many features is the Coffee Shop, a viticulture research and practice blog. Rural coffee shops have long since been favorite gathering places where farmers come together to catch up on local happenings and share farming knowledge about the weather, new technological innovations and market trends.

    The Coffee Shop was designed to be a virtual gathering place where Lodi winegrowers and other viticulture professionals can learn from one another. The contributing authors include viticulture consultants, PCAs, University of California Extension farm advisors, industry leaders, university scientists and growers themselves.

    The Coffee Shop aims to bring a grounded perspective to cutting edge research and innovative practices and technologies. For questions about the Coffee Shop or to submit an article, contact Matthew Hoffman at

Now let’s imagine that you are applying 1 pound of Acramite per acre in a vineyard with 9 feet between vine rows. That means that you are applying 1 pound per 4,840 linear feet of vine row. Another way to say this is that you are applying 3.3 ounces of Acramite per 1,000 feet of vine row.

In one vineyard, you applied Acramite at the low end of the label rate, and in the other vineyard you applied it at the high end of the label rate. However, in each case you applied 3.3 ounces per 1,000 linear feet of vine row. In other words, although the per-acre dose rate was completely different, the actual dose arriving on the grapevine canopy was exactly the same.

This is the new math: 0.75 pounds equals 1 pound! Or at least it can, depending on the tractor row width. This is important because research trial results are reported based on a certain pesticide dose per acre. However, if you do not know the tractor row width of the vineyard where the trial was conducted, then you do not know how much pesticide was actually applied per 1,000 feet of vine row.

If we are going to continue to talk in terms of per-acre dose, then we need to know the tractor row width in the vineyard where the research was conducted. Either that, or the research needs to be reported in terms of linear feet of vine row rather than on a per-acre basis. The same logic applies to sales or technical presentations in which the pesticide dose is given on a per-acre basis.

When we talk about per-acre pesticide dose, we are speaking in terms of area-based calibration, and the unit of measure is the acre. When we talk about pesticide dose per 1,000 feet of vineyard row, then we are speaking in terms of distance-based calibration, and the unit of measure can be any measurement of distance. If we are going to farm vineyards with different tractor row widths, then distance-based calibration makes much more sense than area-based calibration.

There is more to this new math. It is also true that 1,000 linear feet of vine row is not always equal to 1,000 linear feet of vine row.

Imagine a vertically shoot positioned vineyard in Sonoma County, Calif., in May and a vineyard on a quadrilateral trellis in Madera, Calif., in July. The canopy size is completely different! The 1,000 feet of vine row in Madera will have much more canopy to cover than the VSP vineyard in Sonoma. In addition to distance, we also need to adjust the calibration to compensate for the size of the canopy.

The details of how to do distance-based calibration, including how to adjust for canopy size, are clearly explained in “Orchard & Vineyard Spraying Handbook” for Australia & New Zealand by Geoffrey O. Furness, which is available at the University of California, Davis, bookstore. According to Furness, both Australia and New Zealand have switched fro m area-based calibration to distance-based calibration in their vineyards.

If we want to make a similar transition it will not be simple, quick or easy. All of our pesticide labels are written with per-acre dose, and it is a violation of state and federal law to deviate from the label. In addition, our pesticide-use reporting procedures are all based on per-acre dose, as are spray rig calibration practices.

Although we cannot make the transition immediately, I think it is important for each of us to begin to realize that, in modern California vineyards, the use of area-based calibration no longer makes rational sense. The transition to distance-based calibration is inevitable and, in my opinion, the sooner the better.

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