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 I am not an engineer. Neither are most growers, but a lot of engineering has gone into the nozzles used for weed control, especially in the last ten years. It was a lot different when I sprayed my first herbicide trial in 1983; I used brass TeeJet 8002 nozzles. If I wanted more ‘drift reduction’ I could use a larger nozzle, such as an 8004, or choose an ‘LP’ nozzle; remember those? Those nozzles were designed for use at lower pressures. I could use a 11002 nozzle. It didn’t reduce the number of small (driftable) droplets but I could hold the boom closer to the target so it wouldn’t be as affected by the wind. The nozzles available were brass, stainless steel or ceramic.   

Nozzle Revolution

                  A few years later I found the TeeJet XR (Extended Range) nozzle and like many used this nozzle almost exclusively for the next 15 years. They were basically a plastic (polymer) nozzle with a stainless steel core and best of all color coded-02’s (as in 8002) are yellow, 04’s (as in 8004) red and so on. We could adjust the pressure from 20-60 psi and still get a pretty consistent pattern.

                  Then the nozzle “revolution” started. TeeJet introduced venturi nozzles like the “AI” or air Induction and the “chamber nozzles” like Turbo and Turbo TwinJet nozzles and now the Turbo TwinJet Induction TTI; GreenLeaf had the “Turbodrop” and others. Each of these nozzles had some kind of chamber where the spray wasn’t forced directly out of the nozzle tip. Many growers began to use these nozzles to get good coverage and reduce drift potential.

                  Today we have a wide range of nozzles available for use when making herbicide applications in orchards and vineyards. But have we really examined these new innovations in nozzle technology? In my travels I have seen many, not all, growers using these new nozzles (if it ain’t broke why fix it?). Unfortunately, many aren’t using them properly. So what’s different about these new nozzles? It all comes down to droplet size (see Figure 1.).

                  The following quote is taken from a Pesticide Environmental Stewardship document titled “Understanding Droplet Size:” “The Volume Median Diameter (VMD) refers to the midpoint droplet size (mean), where half of the volume of spray is in droplets smaller, and half of the volume is in droplets larger than the mean. A VMD (DV0.5) of 400, for example, indicates that half of the volume is in droplet sizes smaller than 400 microns, and half the volume is in droplet sizes larger than 400 microns. Some pesticide labels specify a recommended droplet size. An example would be: “Use nozzles producing a coarse (VMD of 400 or greater) droplet category.” 

Herbicide Applications and Coverage

                  So how does that effect herbicide applications? In a word: coverage. The amount of coverage needed is determined by the type and size of target weed (grass or broadleaf, large or small), application timing (preemergence or postemergence) and the activity of the herbicide (contact or systemic). The smaller the droplet size the better the coverage. Unless the droplets are too small and actually dry up before hitting the target, which is a subject for an entirely different article. In general, herbicide applications in orchards should be made with nozzles delivering a droplet size (VMD) of 250-500 microns (Medium to Very Coarse).

                   An example of when it would be better to use a larger droplet is when using a systemic herbicide, like glyphosate, on a plant with large leaves, like a mustard plant; a target that is easy to hit and a systemic herbicide that should be able to move within the plant to control it. But what about using a contact herbicide, like paraquat, on small grass plants? Larger droplets may not provide the coverage needed to hit the small targets. In this scenario you may have to increase your spray volume (more droplets), or use a nozzle that is delivering a smaller droplet size. The trick when selecting nozzles is to be at the intersection of good coverage and drift reduction.

                  Figure 1.

                  droplet size

(Copyright Pesticide Environmental Stewardship. Initial compilation courtesy of Jim Wilson, PhD. South Dakota Cooperative Extension).

                  Figure 2.     

                    Picture1 xr     

                       Picture1 aixr                     

                  I am concerned that we are not using these “new” nozzles properly and longterm weed control may suffer. Figure 2 shows the chart of two types of nozzles from TeeJet. First the nozzles on this chart that correspond to the colors ( Blue 03, Red 04, etc) both deliver the same volume of water at the standard (40 psi) pressure. An 02 (11002 or 8002) delivers 0.2 gallons of spray solution per minute and the 04 (11004 or 8004) 0.4 gallons of spray solution per minute at 40 psi. But as you would expect the droplet size changes, quite a bit in some cases. Looking again at Figure 2, the XR8004 nozzle at 40 psi correponds to an  ‘M’ for medium droplet size or a VMD range of 226-325 microns. Staying at 40 psi but changing to the AIXR11004 nozzle will produce a droplet size ‘XC’ or extra coarse (EC on color code chart) with a VMD range of 501-650 microns that is twice as big as the XR8004. A Turbo Teejet TT11004 nozzle at 40 psi (not shown) produces an UC (ultra coarse) droplet size which is defined as VMD more than 650 microns. These larger droplet sizes will provide good drift control but may not be the best in every situation, as described above.

Drift Control

                  If you need drift control but have determined that a ‘Coarse’ or ‘Very Coarse’ droplet size would be more appropriate for your target weeds you have a couple of choices and both will require a new calibration. (Note:  calibration, or at least a volume test, should be done every time the sprayer is used). If you use the AIXR11004 nozzle you can increase the system pressure to 70 psi, or keep the pressure at 35 or 40 and change to a AIXR11002 nozzle. They will both produce about the same sized droplet profile—but the AIXR11004 now will be delivering 0.55 gallons per minute (chart not shown) and the AIXR 11002 should be delivering 0.2 gallons of spray solution per minute at 40 psi. So you will either have to speed up, or slow down, to stay at the same gallons per acre. It would be better to recalibrate your application using these new parameters.

Off-Center Nozzle

                  The standard practice in many orchards and vineyards is to spray down one side of the row and then come back on the other side. The ‘OC’ or Off-Center nozzle, like the one pictured below is often used at the “tree- end” of the spray boom. The nozzle that is most often used is the same design that has been used for 50 years and can produce a lot of “driftable” (small) droplets. Newer designs are available such as the TeeJet AIUB nozzle. The problem is the same for any off-center nozzle design when it comes to uniform coverage. Why is an OC nozzle needed? Standard flat fan nozzles are designed to be used in an overlapping configuration and are often positioned at 20-30 inches apart. If you don’t use an OC nozzle and were to spray close enough to achieve this overlap you would need to be 20 inches from the other side or 10 inches from the middle of the tree. The OC nozzle can be used to replace the “missing nozzle.” They can be set 40 inches apart or a safer 20 inches from the middle of the tree. However, this nozzle is often farther, in some cases much farther, out than 20 inches from the tree. To get the same coverage as the rest of the boom the output from the OC nozzles must overlap 80-100 percent when you come back around the other side of the tree; a fact surprising to many growers. Many growers try and overcome this by putting a flat-fan nozzle and OC nozzle in tandem at the end of the boom. At this point the OC nozzle is directed at a higher angle which may or may not overlap. I am amazed that for every other nozzle the height and spacing are very specific. Try to find any literature on the use of an OC nozzle that says more than “use on the end of orchard herbicide spray booms.”

Uniform Spray Pattern

                  Having a uniform spray pattern is important for even coverage and weed control. I use the TeeJet Pattern Check to collect the spray solution and determine the coverage. When sprayed from both sides the red ball indicators should be almost flat reflecting that the same amount of water is hitting each area. My experience is that in most cases the middle of the tree row receives less spray solution, therefore a lighter rate of herbicide than areas farther out yet the middle of the tree row is the area that often gets more irrigation with micro-sprinkler or especially drip irrigation and where weeds are more likely to grow. I recently learned more about boomless flat fan nozzles. These nozzles, such as the TeeJet BoomJet or Hypro Boom X Tender and others, have been used in the roadside and turf industries successfully for years. As yet they have not been used widely in orchards and more research is needed to determine if they can be successful there as well.

                  The take-home message is to choose the right nozzle for each situation while attaining the best drift reduction possible and still getting the performance needed for good weed control and checking to make sure that the nozzles you are using are getting the herbicide where it needs to go.

(Note: My reference to TeeJet nozzles is not a recommendation, but simply nozzles with which I am familiar. HyPro, GreenLeaf and others also manufacture similar nozzles)