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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) 


Every year, hungry hives are placed in orchards before the dawn of almond bloom. In growers’ experience, hives that forage on cover crops early (before bloom) are stronger in the second week of February, when almond bloom usually occurs. What’s more, cover crops planted in orchards provide bees with nutrients, allowing growers to boost their pollination potential.

In addition to providing better bee health, cover crops improve soil health in the orchard. Orchards will have better water infiltration, earlier field access, reduced compaction and better nitrogen contribution if the right mix is used. All cover crops excel at increasing organic matter, an important, yet often overlooked, aspect of soil health. Organic matter holds 18-20 times its weight in water. In fact, a 1% increase of organic matter in soil can hold up to 19,000 gallons of water per acre!

Here at Project Apis m. (PAm), understanding cover crop impact on orchards is part of our persistent tracking and funding of honey-bee-related research. Located at the nexus of two complimentary industries – almond production and pollination – PAm develops programs, such as Seeds for Bees, that fit the needs of both beekeepers and growers.

Launched by our experts in 2013, Seeds for Bees is a free bee forage cover crop program that almond growers with orchards of all sizes use to take advantage of the many mentioned benefits of cover crops. Demand for Seeds for Bees has grown steadily. Last year, the program provided 6,200 acres of cover crops to California growers, up significantly from 2,100 acres the first year. Each grower may receive a set amount of seed via Seeds for Bees funding. However, many growers with large acreage will buy additional seed outside the program to supplement coverage of their entire orchard.

Planting Cover Crops

With the aim of ensuring an early bloom, the ideal time to plant PAm cover crops is by October 5, before the first winter rains. However, some orchards with late harvesting varieties may not be ready by then. Cover crops planted after October 5 will still germinate, though the hive-strengthening aspects will be diminished. Synchronizing cover crop bloom with the bees’ arrival is the best way to take full advantage of the Seeds for Bees program.

There are three Seeds for Bees options from which to choose:

  1. PAm Mustard Mix is a mixture of Canola, ‘Bracco’ White Mustard, ‘Nemfix’ Mustard, Common Yellow Mustard and Daikon Radish. This mixture is great for adding organic matter and alleviating soil compaction in the orchard and requires the least amount of water among the three options.
  2. PAm Clover Mix is a mixture of six different species including Crimson Clover, ‘Hykon’ Rose Clover, Nitro Persian Clover, Frontier Balansa Clover, Berseem Clover and Annual Medic. Unlike the rapid fall growth of the Mustard Mix, this mix grows slowly over the winter. Clovers are nitrogen fixing plants, adding up to 84 lbs. N/acre.
  3. ‘Lana’ Woollypod Vetch is not a mixture, but a single species. Vetch, like clover, has nitrogen-fixation properties and should be planted early.

The best method for planting is direct seeding with drill equipment. We recommend an orchard/compact drill, equipment sold by companies such as Schmeiser or Great Plains. If broadcast seeding is the only option, a fine seed bed is desirable, since most of the seeds are small, like alfalfa. Ideally, the soil should be disked, cultipacked with a ring roller, planted and rolled a second time. The cover crop can be mowed or disked any time after almond bloom. If reseeding is desired, leaving plants intact until June may be necessary, however, this date will vary depending on the planting date and local climate. Reseeding of the PAm Clover Mix and ‘Lana’ Woollypod Vetch is encouraged, but the PAm Mustard Mix can be aggressive and is not a good candidate for reseeding.

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A new item has been posted at "The Almond Doctor" titled "Almond Postharvest Management: Nitrogen considerations." This article highlights our understanding and some of the research regarding nitrogen management practices within almond. An excerpt:

"Interestingly, recent research suggests that late postharvest fertilization (October) can be skipped if mid-July leaf nitrogen levels are adequate (over 2.5% nitrogen). This work by Franz Niederholzer conducted at the Nickels Soil Lab in Colusa County has found no negative impact on yields when skipping postharvest nitrogen applications within orchards over the past two years..."

A link to the article can be found here:   David

From The Almond Doctor

Aerial imaging can provide real-time information to growers regarding water usage and crop health. Within agriculture, these tools provide a valuable service for identifying problematic areas within fields, thereby increasing efficiencies for both small and large scale producers. Currently, most aerial imaging is conducted by flights with mid-elevation aircraft or satellites. These flights and corresponding images areusually conducted by a service company and provided on a weekly or monthly basis.


Autonomous or Unmanned Aerial Vehicles (UAVs) may provide a format in which more regular flight data can be obtained. Most discussions within agricultural settings have been focused around largefixed wing drones. However, smaller, less sophisticated and less autonomous UAVs could provide a useful platform for California farmers. These smaller UAVs would be less expensive to construct, may require less regulatory permitting, andprovide a mobile 

platform that can be quickly deployed within a field setting. In these settings, small UAVs would have the ability to quickly monitor crops for water stress, nutrient management, and pest and disease epidemics.

A transformed image of an almond orchard using the normalized difference vegetation index.

Almond BloomAs forecasted, the weather for bloom 2017 looks wet. This will impact the number of fungicide applications, how we apply the material, orchard access, and bee concerns. This article is a follow up to what was written last week

Periods of leaf wetness favor fungal pathogen development. Although there are no specific models for blossom pathogens, I general suggest applying a fungicide prior to a rain event in which leaf wetness exceeds 24 hours. This suggests that short, passing storms may not need a fungicide spray, but multi-day storms or multiple passing showers would. With the impending week of wet weather, fungicide applications to reduce the occurrence of disease is strongly encouraged. More on fungicide selection can be found here at the UC IPM website.

Aggregation of leaffooted by on walnut in early October of 2016. The aggregation is comprised mostly of fifth instar.

For a few seasons now, I have been interested in understanding more and ultimately finding better monitoring tools for Leaffooted bug, Leptoglossus spp.  Most growers and PCAs have a  good working knowledge of this bug and likely have attended one or more of my talks covering the subject.  We know that leaffooted bug overwinters in aggregations consisting of just a few to several hundred individuals.  The aggregations tend to occur on citrus, palm frowns, Cyprus trees, pomegranate, walnut (Fig. 1), olive, and on/in non-plant substrates like pump houses, farm equipment, and wood piles.  The list is extensive.  The reason why aggregations can occur on such a diversity of substrates is that they are not necessary interested in feeding but more so in seeking a protected area to survive winter.  An  interesting behavior that I have made is that aggregations typically occur where the group can best collect heat from the sun during peak solar radiation periods.