Virtually everybody, from the corporate farmer to the home gardener, want options that make weed control easier and more effective.  Weed scientists study the biology of weeds and their control.  Studies on weed control include cultural practices of growing the crops that provide a measure of weed suppression, mechanical controls, and herbicides.  Successful weed control is built around an integration of these three components into a balanced system.  The development of selective herbicides and practical application equipment contributed significantly to the modern agricultural revolution of the last few decades.

Managers of food plots for whitetail deer have few herbicides for use on legume plantings.  While the selection is limited, these herbicides can help improve the quality of the food plot, add life to perennial legumes without weed competition weakening the stand, and give managers a measure of satisfaction of a job well done.  In the past, herbicides have not been discussed in detail due to the limited selection and most are marketed to farmers in quantities not practical for managers of food plots.  Furthermore, handheld and backpack sprayers available to managers of food plots are generally not suitable for precise and accurate application of selective herbicides.  Precise and accurate herbicide delivery often determines whether the desired crop is selectively protected from the herbicide or injured.  Precise herbicide application is now possible for managers of food plots with the widespread availability of ATV mounted boom sprayers.

Recently, I have noticed a number of vendors selling boom sprayers that are towed or mounted on the cargo rack of an ATV.  Boom sprayers have a series of nozzle tips mounted horizontally along a rigid boom.  This allows a swath from 6 to 12 ft. wide to be treated in one pass.  The towed sprayer is primarily used on turf or well prepared fields where the soil surface is firm and smooth.  Towed sprayers are probably not practical for use in food plots since the most sites are likely to be rough, even with good site preparation.  Sprayers mounted on the rear cargo rack of an ATV have the greatest potential and can be used on most any site where food plots will be located.

These sprayers have the same general features that agricultural sprayers have, but on a smaller scale.  ATV sprayers have a chemical resistant plastic tank large enough to hold 15 to 25 gallons of spray solution.  These sprayers have an electronic pump that generates pressure, propelling the spray through a series of nozzle tips.  The pump is powered off the electronic system of the ATV, usually with leads attached directly to the vehicle’s 12-volt battery.  These features allow the manager of food plots to uniformly treat a fairly large area with herbicides, using the ATV as the source of horsepower.  This is a significant improvement over using a handheld or backpack sprayer containing a single nozzle, pressurized with a hand-operated pump. 

The keys to correctly using an ATV sprayer are set-up, accurate calibration, and proper operation.  Set-up is assembly plus configuration for optimal application of selective herbicides.  Calibration is a series of mathematical calculations to determine the output of the sprayer (in gallons per acre), which is essential for precise and accurate application of herbicides.  Operation is using the data from calibration to mix herbicides at the correct dosage and techniques to apply herbicides.

From what I can tell, these sprayers have adequate instructions for assembly and the instructions should be followed.  Make sure the sprayer is tightly secured to the rear cargo rack on the ATV.  A filled ATV sprayer can weigh as much as 200 pounds, and that mass can easily bounce free when jostled during use.  Furthermore, the additional weight of a fully loaded sprayer may alter the handling and stability of the ATV.  Once assembled, use water alone (no herbicide) to determine if the sprayer is operating according to the instructions and to insure no leaks are in the system.  This also a good opportunity to become familiar with sprayer controls and operation.

There are many different modifications that can be made during set-up depending on the sprayer’s intended use.  For most herbicide applications in food plots, the suggested set-up will probably work.  It is wise to keep everything simple until you gain experience.

Nozzle Tips

Nozzle tip selection is almost a science in itself and this is a case where keeping it simple makes sense.  Some agricultural engineers devote the majority of their career to spray tip research and development. An excellent reference that discusses the basic facts regarding nozzle tips is http://www.ext.nodak.edu/extpubs/ageng/machine/ae73-3.htm#Nozzles .

Spray nozzle tips are precisely machined devices that help regulate spray flow and disperse the spray into uniform sized droplets in useful patterns (fan-shaped, hollow cone, solid cone, stream, etc.).  Nozzle tips vary in materials from which they are made; nylon, brass, stainless steel, and ceramic.  Nylon is the most cost-effective nozzle tip material for managers of food plots.  It may not be necessary to initially replace the nozzle tips that are packaged with the sprayer, but they are an expendable item and will need to be periodically replaced due to wear.

There is no real reason to be overly complicated when choosing nozzle tips.  Therefore, limit consideration to flood-jet and flat-fan tips.  Flood-jet tips produce a fairly wide spray pattern of large, coarse droplets.  Farmers often use flood-jet spray tips to apply preemergence herbicides (ProwlÒ, PursuitÒ, KerbÒ, etc.) to soil since they are not overly prone to being clogged by loose soil or debris due to their large orifice.  The large droplet size also minimizes spray drift.  However, flood-jet tips are not the nozzle of choice for applying postemergence herbicides (RoundupÒ, PoastÒ VantageÒ, and etc.) since they generally produce a coarse pattern with few droplets and may not provide adequate coverage on emerged weeds.  Also, flood-jet spray tips and their large orifice consume large volumes of water, which will require frequent refilling.  This is critical for large food plots (in this case those greater than one acre) or in remote sites where clean spray water is not available.

The other choice for a spray tip is one that produces a flat-fan.  These tips offer the advantage of producing fine spray droplets of a uniform size, usually with lower spray volumes than flood-jet tips.  A finer pattern gives better spray coverage of weeds, but is more prone to being clogged.  The lower spray volume produced by a flat-fan tip allows a tank of herbicide mixture to be sprayed to a larger area than with flood-jet nozzle tips. 

Regardless of the spray tips chosen, it is highly recommended to use in-line strainers for each tip mounted on the sprayer.  There are two general types of strainers; slotted and screen mesh.  These will filter particulate matter and prevent clogging the spray tip.  The screen itself can become clogged, but it is far easier to clean a strainer than a spray tip.  The fragile spray tip orifice can be easily marred by prying out debris with a pocketknife or a piece of wire. 

My personal preferences are nylon flat-fan tips used with slotted strainers.  They are the best compromise of cost, versatility, and performance.  There are several major manufacturers of sprayer components for agricultural use and three of the most common are Spraying Systems (http://www.teejet.com/), Delavan (http://www.delavan.co.uk/), and Hypro (http://www.hypropumps.com/).  These companies have excellent web sites, high quality brochures on sprayer use, downloadable technical sheets, and customer service.  They can offer qualified advice on spray-tip selection and provide a list of local dealers.

Pressure Gauge

Another desirable modification is a functional pressure gauge.  The ability of an ATV sprayer, with the electronic pump to generate and maintain steady pressure, is a tremendous benefit to users.  Pressure that the pump generates is the means by which the herbicide solution is propelled through the nozzle tips.  Some sprayers have pumps with adjustable pressure and some have fixed pressure.  A functional gauge makes it possible to monitor pressure during operation.  Widely fluctuating spray pressure is often a symptom of a sprayer malfunction that affects precision and accuracy.

Pressure gauges are notoriously fragile and frequently become inoperable.  Fortunately, replacements are readily available at industrial gas suppliers and agricultural equipment dealerships.  Retrofitting or replacing a pressure gauge on an ATV sprayer is a simple task.

Arrangement of Spray Nozzles and Spray Boom Height 

The number of spray tips, spacing on the boom, and angle of alignment are determined by the nozzle type and height of the boom.  Farmers have sprayers with wide adjustments in boom height and nozzle spacing, giving them many options.  They simply set the hydraulically adjustable boom height based on the nozzle tips used.  Some ATV sprayers have a fixed boom height, while others have a limited amount of adjustment.  It is important to mount and secure the sprayer on the ATV that you actually intend to use for spraying, since boom height on ATV mounted sprayers may differ according to suspension, tire size, and overall height.  Refer to the published data from spray tip manufacturers for correct boom height and nozzle spacing. 

Remember simplicity.  If the entire process of nozzle tip selection is too complicated, intimidating, or critical information simply not available, stick with what the ATV sprayer was originally equipped, and follow our guidelines for calibration and operation. 

Ground Speed Determination and Regulation

Ground speed affects calibration; faster ground speed will reduce the sprayer output (gallons of spray per acre), while slower ground speed will increase sprayer output.  A reasonable ground speed for spraying is 2 to 4 miles per hour.  The key is knowing the ground speed and maintaining the ground speed.  Many ATVs that I have seen have neither a speedometer nor a tachometer.  If one is to be added to the ATV, my recommendation is the tachometer.  Farmers do not use the speedometer on a tractor to accurately determine ground speed.  They choose a gear, range, and tachometer reading (engine revolutions per minute) to act as reference point on which to calculate their speed.  At these engine settings, they determine the time needed to travel a set distance.  From that, they calculate their speed in miles per hour.  Refer to Table 1.  This is a simple listing of the times needed to travel 50 and 100 ft. and the corresponding speed expressed as miles per hour.  If an ATV does not have a tachometer, choose a gear and throttle setting that can be replicated and maintained, calculate the ground speed, then calibrate and operate the sprayer at those settings.

An often-overlooked factor is the need to calculate the speed of the ATV in soil conditions similar to those where the sprayer will be used.  Tires slip in loose soil.  With the same gear and throttle setting, ground speed on hard pavement will differ from ground speed on loose soil and this difference could cause a large calibration error, altering herbicide rate.

After the sprayer has been set-up, calibration is simply an exercise in algebra.  That is the topic in the next article.

Table 1.  Times needed to travel test distances to achieve ground speeds in miles per hour.  Speed variation is achieved by adjusting gear and throttle settings on the ATV or tractor.¹

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¹Determine ground speed under soil conditions similar to those where the sprayer will be used.

LIST OF FIGURES

Figure 1.  Example of ATV sprayer with optional spray boom.  API Outdoors makes this sprayer and boom.  Critical features include chemical resistant spray tank, pump that operates off the ATV battery, and height adjustable aluminum boom with flat-fan nozzle tips.  

Figure 2.  Arrangement of spray nozzles on the boom made by API Outdoors.  In this example, nozzle tips are spaced 20 inches apart with a boom height of 20 inches.  Using this configuration, the sprayer can accurately spray a swath nearly 12 feet wide. 

Figure 3.  Examples of common spray nozzle tips, materials of construction, and screens.  Top:  flat fan tip made of nylon and cap for quick disconnect from nozzle body.  Middle row from left to right:  Delavan® flat fan tip made of nylon, Tee Jet® flat fan tip made of brass, Tee Jet® flood jet made of nylon.  Bottom row from left to right:  50-mesh screen strainer, brass slotted strainer.  Generally, any of these items will work on ATV sprayers.  It is important to not mix and match spray tips and strainers of differing brand, type, and construction material on the ATV sprayer.  Using components of the same size and type will to help ensure accurate and precise herbicide application.