How to Calibrate and Use a Backpack Sprayer

 

Rick Dunst, Viticulturist, Double A Vineyards, Inc.

 

 

Small vineyard owners often find that they need to spray chemicals for control of weeds, insects, and disease, but can’t justify the expense of a tractor-operated sprayer (not to mention the tractor). The need for chemical applications to control grapevine diseases can be minimized by selecting cultivars that are relatively disease-resistant, and by planting the vineyard in a location with full sunlight and good air movement. However, in humid climates, some fungicide applications are almost always needed to maintain a healthy canopy of leaves and/or disease-free fruit. Most fungicides are applied to prevent the development of diseases, while insecticides are usually applied when insects are present and have met or exceeded established thresholds. In very small vineyards weeds can be controlled by hand-pulling or hoeing, or by applying organic or synthetic mulches, but larger vineyards often require the application of chemical herbicides. Finally, wildlife predation by deer, rabbits, and birds is sometimes accomplished with the use of exclusion devices such as fences and netting, but repellant sprays are sometimes needed to minimize predatory damage to young vines or to fruit.

There are many brands of backpack sprayers on the market that are completely hand- (and foot-) powered. Double A Vineyards sells a “Deluxe” Solo brand sprayer that holds 4 gallons of water or spray mix and has a pressure gauge to ensure an even application rate. The sprayer is pressurized with a hand lever pump. While spraying, keep pressure constant by pumping down on the lever and maintaining a steady reading on the pressure gauge. The Solo Deluxe sprayer includes several nozzle types. Many standard agricultural spray tips can also be used – use whatever nozzle gives you the spray coverage you are looking for.

When making foliar applications of fungicides or insecticides to the canopy, thorough coverage of the target (leaves and/or fruit, depending on the pest to be controlled) is necessary. Canopies need to be sprayed from both sides of the row. Application instructions found on the label of the product you are using can be based on an amount of pesticide per volume of spray mix or as an amount of product to use per acre of vineyard. Examples include the following:

Some pesticides packaged for the homeowner provide instructions based on an amount of pesticide per gallon of spray mix. For example, label instructions for Bonide Captan 50WP state, “Use 1 to 1 ½ Tbs. per gal. of water. Apply sufficient spray volume to provide thorough, even coverage…. Use the lower rate when spraying less susceptible grape varieties or when conditions are less favorable for disease development. Use the higher rate on susceptible grape varieties and during periods of weather highly favorable for disease development.” In other words, mix the desired amount of product per volume of water, and apply so that all target fruit and foliage is covered, but not so much that the spray is dripping from the canopy. Another example of a pesticide that is applied as a percent solution is JMS Stylet Oil, often applied to control powdery mildew. The stylet oil label instructs, “Apply at 1-2 gal per 100 gal. water (a 1-2% solution). Spray for optimum coverage of leaf surfaces. For powdery mildew control, use the higher rate … when disease conditions are severe.” In order to achieve optimum coverage, sprays should be applied to, but not beyond, the point of runoff.

As opposed to application rates based on an amount of product per volume of water, most commercial pesticide products are labeled for application at an amount of product per acre of vineyard. This type of application will require careful sprayer calibration. Let’s use the example of Microthiol Sulfur, which is labeled at application rates ranging from 3-10 lb. per acre per application for control of powdery mildew, and you want to apply this product at a typical application rate of 5 lbs. per acre. In order to make this application correctly (and legally), you need to know how many vines there are in an acre of your vineyard, and how many vines you can spray with a given volume of spray solution. Sprayer calibration should be performed using a known volume of clean water in the sprayer. For example: your vineyard is planted at 8’ x 6’ spacing, with 908 vines per acre (determined from the table in our catalog, or by using this formula: Vines per Acre = 43,560/ (feet between rows x feet between vines. 43,560 is the number of square feet in an acre). Fill the sprayer with a known quantity of water, and spray the vines to obtain the desired coverage from both sides of the vines until the sprayer is empty to determine how many vines are sprayed (alternatively, spray the vines from one side of the row and divide the number of vines sprayed by 2). For this example, let’s assume you spray 10 vines from both sides with 1 gallons of water. Divide the number of vines per acre by the number of vines sprayed with one gallon of water to determine how many gallons of water are necessary to spray one acre of vines. In this example, 908 vines per acre / 10 vines sprayed with one gallon = 90.8 gal./acre. It will take 90.8 gallons of water to spray one acre of grapes. Since you want to spray 5 lb. sulfur per acre, mix 5 lb. (80 ounces) sulfur per 90.8 gallons, or 0.88 oz. sulfur/gal. Use a postal scale or other accurate scale to weigh the sulfur. Dilute spray volumes are usually in the range of 50 to 100 gal. per acre.

Herbicide calibration can also be based on an amount of product to be used per gallon of water or on a per acre basis (but please read the next paragraph for one important difference). Glyphosate herbicide (original trade name: Roundup) can be applied according to label instructions using an amount of product per gallon of water, with the product rate varying depending on the weed species to be controlled. Glyphosate is a systemic herbicide (meaning it is taken up by mature leaves on actively growing plants and translocated throughout the plant). Glyphosate is more effective at higher concentration, so spraying to runoff is not necessary.

Pre-emergence herbicides are applied on a per-acre basis, but an important distinction needs to be made – herbicide rates are determined on the basis of a rate PER ACRE OF LAND SPRAYED, not per acre of vineyard. To determine how many acres of land are sprayed per acre of vineyard, divide the row width by the herbicide band width. For example, if you are spraying a 32” herbicide strip in a vineyard with 8’ rows, you would spray the desired amount of herbicide on 3 acres of vineyard (96” row width / 32” band width = 3 acres of land sprayed per acre of vineyard). Using the same example vineyard used for foliar spraying (8’ x 6’ spacing)), there are 908 vines per acre. Assume you are spraying a 32” herbicide band, so you will spray 1 acre of land in 3 acres of vineyard, or 2,724 vines. For this example, let’s assume 1 gallon of water sprays 100 vines from both sides (or 200 vines from one side). 2,724 vines per acre sprayed / 100 vines sprayed with one gallon of water = 27.24 gallons per acre sprayed. Mix the amount of herbicide desired (i.e. 4 lbs. per acre in 27.24 gal/acre = 0.15 lb. or 2.35 oz./gal.). Herbicides are usually applied at 25 to 40 gal. per acre sprayed.

When applying herbicides with a backpack sprayer, I typically use a Tee-Jet 8004 flat fan nozzle. The “80” in the nozzle designation indicates the angle of spray delivered – use of a higher degree tip would require holding the nozzle closer to the ground for making a band application of herbicide, and would make applications of post-emergence herbicides such as glyphosate (Roundup) more difficult when herbicide contact with grapevine foliage needs to be avoided. The “04” indicates the volume of spray that will be delivered – a lower numbered nozzle delivers less spray volume at the same operating pressure, and a higher numbered nozzle more. In my experience using the Tee-Jet 8004 nozzle spraying herbicide in a 16” band on each side of the row, at a comfortable walking pace and 35 psi, covers 1 acre of land sprayed with 40 gallons of mix. Each operator should calibrate their sprayer at their own pace, using the selected nozzle type, size, and operating pressure.

One response to “How to Calibrate and Use a Backpack Sprayer

  1. Rick,
    Thank you. Both your personal response and the article were helpful and have answered my question . I’ll use my scale to weigh instead of the ancient /antiquated measurement by volume that way I’ll be confident my math matches my mix .

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