Arguably the cheapest part of a spray rig, nozzles are key to making sure expensive spray material is delivered in accurate amounts to the proper spot on the plant or soil.
Anyone who follows auto racing has a favorite story about a race lost because a $5 oil filter or a $3 valve stem malfunctioned. The same kind of catastrophic failure can happen on a farm when the wrong or worn $5 nozzle confounds a $10,000 pesticide or liquid fertilizer program.
To accommodate growers’ needs, nozzle manufacturers offer a wide array of configurations that will apply liquid at the proper application rate in the correct spray pattern. Nozzles are responsible for applying the material in a specific droplet size at a precise rate per acre or per 1,000 square feet. (There are 43,560 square feet per acre.)
In today’s world, “precise” is the most important consideration. Accidentally spray-burn a crop on your home acreage and it is your costly problem. Let spray drift onto a neighbor’s property and you may well have a tragedy combined with a lawsuit. This is especially true when spraying broad-spectrum materials. It is a real concern. In a study that involved several states, almost two-thirds of the formal noncompliance reports filed against farmers were the result of drift.
On the farm, the producer who chooses the wrong nozzle will lose two other ways: either by costly and potentially damaging over-application of material; or, with under-application that causes streaky or subpar performance and either ruins the crop or requires another trip through the field with more expensive material.
The key, then, is to get the sprayer set up properly and to choose the right nozzle for the job. Since the calculations for figuring rates per acre involve lots of math, and picking nozzles allows fun playing with shiny brass and steel objects, this article will focus on the hardware itself.
Perhaps the most common nozzle is the flat fan sprayer. While it comes in several widths, it generally shoots out a narrow, upside-down V pattern.
The flat fan is good for broadcast spraying. It is more forgiving than some other configurations and will work with a wide range of sprayer pressures.
Flat fans are effective for band spraying, too, providing even coverage in the row. Some extended-range flat fans perform well over a wide range of pressures. The extended-range flat fan is good for soil and foliar applications. Set flat fans up on the boom so they produce a 30 percent overlap on the edges of the pattern.
Hollow spray cones spray a ring pattern. Typically, the output is a very fine droplet. This is good for situations that require full coverage or directed spray patterns such as post-emergence contact herbicide application and insecticide sprays.
Related is the full cone nozzle. It, too, creates a round but full pattern, which is useful for certain applications like broadcast spraying. Full cone nozzles also can work in some banded uses.
Flooding nozzles give a wide-angle flat fan pattern. Set them up on the boom so they produce a pattern where one nozzle’s spray overlaps to the center of the adjoining nozzle’s spray. This gives a 100 percent overlap (half coverage, doubled from each side). Consider flood nozzles when applying a mix of fertilizer and herbicides.
Lastly, there are the solid stream nozzles. Depending on the configuration, they provide from one to as many as a half-dozen solid streams. Typically, these are the go-to choice for liquid fertilizer application.
Nozzles against drift
No matter which manufacturer is your favorite, the odds are good they offer a low-drift nozzle family as part of their product line. Most low-drift nozzles work on the principle that larger, heavier droplets are less likely to go off-course, while smaller, lighter droplets can be distracted from their target by wind or even a light breeze.
Some of these low-drift versions create larger droplets at the same flow rate and operating pressure as could be expected from flat fan nozzles. Those traditional flat fans have a straight bore that carries the spray from the boom to the tip. Low-drift nozzles have an extra little nook before the discharge tip. The detour slows the velocity of the spray material and reduces the pressure at the exit. This results in larger droplets and less drift. Some manufacturers claim the low-drift technology reduces the smallest droplets (under 200 microns) by half or more. On top of that, those droplets that do drift from the target area tend to stay closer to the target plant. So low-drift nozzles reduce the number of stray drops and the distance they travel.
It is not necessary to go to low-drift nozzles to prevent drift. Simply abiding by good spray technique and not spraying on windy days will help minimize the drift potential from any standard sprayer. Still, some insurance from using low-drift nozzles – at a very low cost – is worth considering.
Producers who try to avoid high-pressure situations themselves will sympathize with spray nozzles. They do not like high pressure, either.
No matter which nozzle type is used, keep in mind that higher pressure decreases the size of the droplet produced. This always increases the potential for drift.
In addition, higher pressure will produce more wear and tear on the orifice. Pressure differences change the spray angle and thus the coverage of the nozzle.
Each nozzle has a somewhat different performance profile. That information is detailed in the manufacturer’s catalog.
Since most nozzles will produce a range of droplet sizes, manufacturers average the advertised numbers under formulas approved by the American Society of Agricultural and Biological Engineers Standard S572 or the British Crop Production Council. Both are good, reliable figures. You can trust either ASAE or BCPC.
There are some rules of thumb.
For one, liquids less dense or lighter than water generally will form wider spray angles. Liquids more dense than water will form smaller spray angles. A good example of the latter is 28 percent liquid nitrogen. The spray angle with liquid N will be smaller than what some producers see as normal.
Coarse droplets, the biggest ones, are desirable when using systemic herbicides and minimizing drift is vital.
The mid-sized droplet is best for contact and systemic herbicides, preemergence surface applications, insecticides and fungicides.
If absolutely precise coverage is critical – think expensive postemergence materials – go to a nozzle with a fine droplet. It will give the best, most thorough coverage of the target leaf surface.
It probably took you long enough with a calculator to figure out the proper spray rate for the job. That does not mean it is time to rush out and start spraying.
Before filling a spray rig, be sure to have your PPE (personal protective equipment) handy. Wear it. This includes rubber or synthetic gloves, protective eyeglasses or goggles, boots, a protective rubber apron and first aid, in case the unthinkable happens.
In the latter case, the first aid should include activated charcoal, soap and an eye wash. Clay granules, crushed lime or sawdust also should be handy in case of a spill.
A personal note: When filling tanks, be sure to protect those nearby. My daughter was watching a tank being filled by a fully protected worker. She wore only street clothes. When the material splashed, she got hit in the face with the chemicals. Fortunately, a large supply of water and first aid equipment was at hand. While painful at first, she suffered no permanent damage. Protect everyone when handling chemicals. – CH
Making the spray
Nozzle size and ground speed of the sprayer are the two factors a farmer can control, change or vary when making a spray application.
For minor adjustments, look at nozzle spacing on the spray boom, spray width and the amount of pressure delivered through the system. As a rule of thumb, to double the spray volume, increase the sprayer pressure by a factor of four.
Another possibly easier way to control application rate is to vary ground speed.
Before taking off, fill the tank with water and run the system to expose any leaks at the tank, shut-off valves or hose fittings. Look at the spray pattern. (It’s safe to do that now since you are pumping only water and not chemicals.) If the pattern seems distorted at one nozzle or another, replace the suspect part. Spray tips can be air blasted. Be sure not to scratch them when cleaning. A spray nozzle showing even 10 percent wear will corrupt the spray pattern and reduce performance.
Calibrate the equipment to the speed of the tractor, or, on self-propelled sprayers, to the unit. This will require a calculator. Remember, speed affects application rate.
Some farmers use cluster nozzles. These nozzles have no boom. Rather, the spray comes from one central point. One benefit of cluster nozzles is good coverage at lower volume. Spray volumes as low as 25 to 50 gallons per acre are possible while still covering a lot of ground.
Coverage is key with cluster nozzles. Since the droplet size will vary, an anti-drift agent should be added to the tank mix.
Sometimes the job calls only for spot-spraying. In this case, a low-volume spray from a backpack sprayer may work. First, be sure the backpack sprayer has nicely padded arm straps. Backpacks are handy for handling tall weeds or brushy plants not much above head height. Spray to cover at least half of the foliage area of the plant. Especially with woody brush, spray all around the tree and hit any greenery on sprouts coming up.
In cases where a straight, single stream nozzle is used, start at the top of the weed and spray from top to bottom in a zigzag motion. If the spray is coming through a flat fan or cone-style nozzle, typical with mist sprays, a similar pattern should be followed while striving for full coverage of the green areas of the target plants.
Keep in mind the nozzle’s construction material. Brass may be the most common material, but it also is the fastest to wear out. Some brass nozzles in tests showed a costly 10 percent increase in product flow after just 50 hours of use.
Plastics, typically with stainless steel or ceramic inserts, will last two to four times longer than brass nozzles. Plastic nozzles also cost less than straight stainless steel. Keep in mind that plastic is prone to physical damage from mishandling or dropping. Still, absent abuse, they provide a good, long life.
Stainless steel will give four to six times the lifespan of brass.
Ceramic nozzles are costly but last the longest, providing a consistent flow throughout their life. Plus, they will last anywhere from 20 to 50 times longer than brass and five to 10 times longer than stainless.
Material choice may range from the imperative (a pesticide manufacturer’s recommendation based on the kind of material being sprayed) to the arcane (driving distance to the parts shop). No matter which type of nozzle a farmer chooses – and there are good reasons for each – do not mix material construction types on the same boom at the same time. Always use the same type of nozzle at the same time.
Rounding it out
At this point, it should be safe to add the fertilizer or pesticide to the spray tank.
If doing a tank mix, experts recommend adding the wettable power formulations first and then the dry flowable materials. Follow that with any emulsifiable concentrates, then water-soluble liquids. Lastly, add the surfactants, anti-foam, wetting or sticking agents required to get the material through the spray nozzles and onto the plant.
In addition to an array of nozzles, there are several other items that should be part of the spray kit. One is personal protective equipment gear (see sidebar on page 21). Another is a wind gauge and weather radio. Third, have a copy of the herbicide label handy and double-check its instructions and requirements versus what you figured for the day’s work.
Why the wind gauge? Both ag engineers and chemical companies advise against spraying when the wind speed is over 10 mph. For volatile materials, the wind speed should be under 5 mph. If in doubt or you must spray today, there are drift control agents that will help keep the spray where you want it to go and not onto the neighbor’s prized rose bushes.
The weather radio will give you a shot at making your spray into a rain-free period if that is recommended on the product label. Likewise, some materials have temperature windows for application. In general, avoid spraying in the rain. Not only is it uncomfortable but it can rut the field and cause product failure that is not the fault of the manufacturer, so there will be no refund.