Surfactants – Making Water Wetter
January 3, 2008
It may sound funny, but water does not always wet well….
Remember, as a kid, when you poured water on the dry soil in the yard and it just beaded up and did not seem to wet the dust and go into the soil?
That was because the drops in the water had high surface tension (caused by internal electrical charges that hold them together as drops and don’t let them spread), and so the individual drops would sit there practically as little beads and not really wet the soil until we stomped on them, then they finally wet the ground.
This is great when the wax finish on your car is still good since the rain droplets will “bead-up” on the hood and not really wet the surface, as they are repelled by the wax. The impermeability of the wax on the car’s body, and the surface tension in the rain droplets come together and really keep the water from “wetting”.
Water is a polar molecule: it has both positive and negative ends.
When these ends are linked by an electrical charge, a chain forms and droplets occur. This is called Hydrogen Bonding and is the cause of surface tension.
Mind you, this is not the tension of the surface that the droplet is to land on, but the tension on the outer surface of the actual droplet that, in effect, holds it together and keeps it from collapsing and spreading on the surface it has landed.
Breaking down this surface tension allows the droplet to collapse and spread over surface, wetting it thoroughly without running off, and that precisely is what we want our sprays doing to our crops.
There are many different types of products developed not only for agriculture but many other industries that need to get the most out of their water’s wetting abilities, that will break down the surface tension and make the water “wetter”.
These are called by many names, such as:
- Adjuvants
- Extenders
- Spreaders
- Spreaderstickers
- Surfactants
- Wetting agents
- etc.
These are all formulated from a wide spectrum of chemistry, from all natural vegetable oil emulsifiers, detergents, and fatty acids, all the way to organo-silicones, emulsifiable oxidized polyethylenes, ethers and even alcohols.
First of all, let’s get the names right.
An Adjuvant is defined as any substance added to a pesticide in order to improve its performance.
A Surfactant is a substance added to the spray solution to reduce the surface tension so that droplets spread out and adsorb to a greater surface area.
Now, to make things simpler, we are going to use the word Surfactant as a general definition, because what we are most interested in is getting our sprays to spread and therefore work better at lower a cost.
Surfactants overcome the effects of beading or surface tension. The surfactant molecule has one end that is soluble in oily or waxy substances, and a second that is water soluble. When a surfactant is added to water and oil, its molecules align themselves at the appropriate ends of the interface and pull the layers together, reducing the beading, or surface tension.
This is visible on the leaf surfaces as the surfactant molecules pull the water and the wax (on the leaf surface) together, causing the droplets to spread out.
Aside from trying to get the best coverage and spread on the crops, we also use surfactants to keep our tank mixes in suspension. This is especially true with Wettable Powders, which usually do not dissolve in the water, such as instant coffee, but remain in their original form:
tiny, micro-pulverized particles that become surrounded by water, which then transports them to the target in the spray and deposits them on the surface, after which, when the water evaporates, these particles go to work.
In other words, water is the carrier.
If that water is not “conditioned” and made wetter, the wettable powders do not readily mix with the tank solution and many times bunch up in tiny groups of many particles which then, when sprayed out on the crop, settle in clumps and do not get spread evenly on the target surfaces. Then you have poor coverage, because the chemical is not evenly distributed.
The basic rule on Wettable Powders is that a Surfactant must be used every time, even if it is only a laundry or dish washing , soap or detergent. (By the way, detergents such as Tide, Dawn, Ivory, Lux, etc. make excellent surfactants, especially in hot weather).
The Jar Test
Labels and literature will refer to a compatibility test system called the “Jar Test”. Try this before you mix your next batch of pesticides:
- Fill a glass jar with water and sprinkle some wettable powder into it
- Shake it well and set it down on a table
- Now, take another jar, fill it with water, sprinkle the same amount of a wettable powder and add a drop of dishwashing liquid
- Shake well and set it down on the table
Come back and look at the jars some five to ten minutes later:
- The first jar will show the powder settled at the bottom
- The second jar will show the contents mixed as they were after you shook them
The dishwashing liquid’s surfactants have “made the water wetter” and have suspended the particles of the powder, not dissolving them but making them part of the solution.
Use this test also to make sure the different materials you are mixing into the tank do not have some adverse reaction among themselves.
Reactions between materials will show up as “layering” in the water where the incompatible materials reject each other and separate into layers. (this is great if you are a bartender making exotic drinks, but a no-no for tank mixes.)
When you have a “layering” condition, try adding a surfactant. If layering does not occur after minutes, you can safely mix the formula, as the reaction was not evidently chemical, but a problem of solubility.
Factors Affecting Surfactants
Surfactants cannot be used across the board, especially in warm sub-tropical and tropical climates, such as Florida, the Caribbean and Central America. There are several factors that have to be considered because of temperature, humidity, and leaf surfaces.
Temperature, along with solar intensity is a prime culprit in spray crop damage. Many publications, texts, labels and crop advisor’s insist on avoiding spray applications during the heat of the day.
This is especially critical on delicate crops in high temperature growing areas. It can also be aggravated by the use of a surfactant with pore sealing characteristics such as oils, silicones and polys, as these do not readily break down or evaporate, but on the contrary, seal the stomas, inhibiting transpiration.
Consequently, logical and careful selection of a surfactant will prevent potential crop damage and/or phytotoxicity.
Humidity is another important factor that affects the performance of the spray on the leaf surface. Especially when that humidity is intense, such as rain.
A soluble surfactant, such as detergent will wash away and carry the chemicals with it. However, a very non-soluble surfactant with “sticking” characteristics, may be too sticky and plug up the stomas.
This is really no problem with herbicides, on the contrary, we are killing and want to keep the material on the leaf, no matter what. So a real Sticker will not only prevent wash-off, but also allow us to reduce our formulation and get more coverage for our dollars.
However, with pesticides and nutritionals we should try to schedule our sprays in cooler times where we can safely use surfactants with organo-silicones, polys and/or ethyls that will not wash off.
The best times to schedule these sprays is towards the evening, which also works well if the wind dies down, preventing excessive drift.
Leaf Surfaces are an often overlooked factor in surfactant selection. Leaves can be smooth, brittle, waxy, hairy, or rough. This is Nature’s way of protecting the plant’s production areas, and sprays will react differently when trying to land on these varied surfaces.
Here again, common sense is probably the best method to select the best surfactant to use, depending on what the target is presenting as a landing pad.
Detergents will work well with most surfaces, but are susceptible to washoff. Fatty acids and oils, both vegetable and petroleum, are not the best for waxy surfaces, yet do well on all others. Organo- silicones, Polys and esters will give you good coverage across the leaf spectrum but must be used with extreme care in heat, especially with delicate foliage.
Summarizing
Good applications are possible using inexpensive surfactants such as household soaps, detergents, fatty acids and oils. A natural approach to what we put on our crops is always a plus, and in this case: simple, effective and economical.
The more specific surfactants being marketed by a host of ag chemical companies are just that: more specific, for more specific applications, more expensive and with a certain amount of risk if not used properly, especially in our extreme climates.
These products are formulated for the entire cross section of the US growing areas, of which Florida, some parts of the Southeast US, the Caribbean and Central America are not representative. What works in Ohio may burn our crops in Ruskin, and so on.
So my advice to you is use your common sense, your experience as a grower, when deciding what to put in your spray water. Salesmen, advisor’s, even this writer are not growing your crop – you are, and you will have to live with the results.
Be conservative and logical and your plants will thrive.
Nozzles Tips – Critical to Effective Spraying and Coverage
January 2, 2008
Spray Tips, or Nozzles, as we call them perform the functions of metering the liquid and then atomizing and distributing it into the desired pattern, or the pattern that comes closest to what we want to do in the field.
Good quality accurate spray tips are critical to the success of the operation and yet they are rarely checked for wear or visible damage, which often results in ineffective application, coverage, crop damage and loss of yield.
We tend to be frugal up front by saving as much as possible on the spray tips, when really we should be thinking of investing in the assurance that they will perform properly and give us better results in the long run. Installing nozzles that will resist wear and calibrating them on a regular basis will save money in chemicals, alone.
A 500 acre farm using nozzles that have a wear of 10% will add over $4500.00 to its chemical costs. And then you add the cost of the inefficient applications, crop damage and low yields. Just imagine what you have been pouring down the drain, so to speak!
Tips should be correctly maintained, with regular checks for visible damage and inaccurate flow. You should replace your tips when the original flow rate goes over 10%.
How Do You Calculate Wear?
The nozzle industry works on a parameter that indicates that a brass nozzle at 200psi will achieve a 10% wear in 10 hours. Just think how long you’ve been running your nozzles out there without even thinking that they may be wearing.
Other materials are more expensive than the standard brass tips, and the wear resistance increases with the material hardness and, of course the cost.
However, a few years ago the Europeans made a breakthrough in producing nozzles in Polyacetal, an “engineering plastic” material which, with the help of the latest computer technology, can be precision molded to extremely fine tolerances. Also, where other plastics such as nylon readily absorb water and swell up in the process, polyacetal is particularly stable. Perhaps the most striking quality of polyacetal tips is their remarkable resistance to wear – superior even to stainless steel.
Relative Nozzle Tip Wear Life
Material —- Wear Factor
Brass-Aluminum 1
Stainless-Steel 2 to 3
Hardened Stainless Steel 10 to 15
Ceramic Lifetime
Carbides (Tungsten, Chrome) Lifetime
The above shows the wear factors of the common spay tip materials in the low to medium price range. Ceramic and Tungsten Carbide spray tips, which have a practically negligible wear factor, are three to five times the cost of spray tips made out of the materials shown on the chart. Polyacetal tips are available in most popular configurations such as fan, disc/core, hollow cone and deflected fan tips.
Choosing the Right Spray Tips
Droplet size and spray quality are affected by various factors, including the properties of the liquid, specific gravity, viscosity and surface tension. The applicator can significantly influence the quality of the spray pattern by the choice of:
- Nozzle Type – A hollow cone tip will generally produce a finer spray than a fan tip of the same output, pressure and spray angle.
- Nozzle Size – A small output spray tip will generally produce a finer spray than a large one – given the same nozzle type, spray angle and pressure.
- Operating Pressure – The spray from any tip will become finer as the pressure is increased.
- Fan Spray Angle – A 110 degree fan spray tip will give a finer spray than its 80 degree counterpart, where output and pressure are the same.
Choosing the Correct Application Rate
The spray volume or application rate is normally recommended on the chemical label and expressed in gallons per acre or liters per hectare, with upper and lower limits. Select the application rate on the basis of:
- Chemical label information or consultant data
- Special crop requirements – penetrating a dense canopy may require the higher end of the volume range
- The limits of the sprayer pump capacity at the PTO speeds to be used. Always allow plenty of spare capacity for agitation – especially with wettable powders
- If in doubt, use the high volume rate, ensuring that the spray quality is consistent with what has been recommended
Spraying in Wind
Windspeeds are critical when spraying. Spraying when it is too windy leads to poor application patterns as well as drift. Great care must be taken when assessing wind speeds before and during spraying.
Following are some guidelines for observing the effects of the wind. Generally, wind speeds of 2 to 5 mph are ideal for spraying.
- Less than 1 mph – calm – smoke rises vertically
- 1 to 2 mph – Light air – smoke drifts off
- 2 to 4 mph – Light Breeze – leaves rustle, wind felt on face
- 4 to 6 mph – Gentle Breezes – leaves and twigs in constant motion
- 6 to 9 mph – Moderate – small branches move, raises dust or loose paper
Setting The Boom Height
Each tip on a spray boom must not only deliver the correct flow rate, but must distribute the spray evenly across the boom width.
When using flat fan spray tips, the spray from each tip should overlap the neighbor’s by at least 50%. This is a function of tip height and spray angle.
When using hollow or full cone pattern tips, the boom height should be such that the edge of each pattern touches the edge of the neighbor’s pattern at the target height.
To test the even pattern of your spray, regardless of the nozzle type, fill the sprayer with clean water and spray an area of dry concrete. If the surface dries leaving “wet streaks”, the application is incorrect and the boom height should be adjusted so that the surface dries out evenly, assuming that the nozzle tips are in good order and are spraying correctly.
Spray Nozzles Wear and Tear
January 2, 2008
An Inside Look at Nozzle Orifice Wear Water and Damage
When we travel, we look at rivers and gorges and canyons and we’re told by the guides how they were formed by the erosion caused over time by flowing water.
How that water, over thousands of years, cut a path through solid rock to form the gulches and crevasses that the rivers now run through, and we’re really impressed and awed at what water could do. Yet we never ever thought that the same water could do the same to the spray nozzles on our equipment.
Yes, we never realized that water, now mixed with particles of metals and ceramics, the common components of many spray materials, could wear out the orifices in the nozzles on our sprayers.
Well, it can and will. Water is abrasive, and the materials we mix into it are even more abrasive. To such an extent, that a brass nozzle’s orifice will begin to wear after only 10 hours of use at 100 pounds pressure.
Nozzle wear means that the orifice of the tip, so carefully engineered to produce an optimum spray pattern becomes deformed, which distorts the spray pattern, producing droplets that are larger than intended, uneven band application and, of course, higher volumes of material per plant or per acre.
Larger droplets cause the spray material not to coat the leaf surface, but to wet it and then slide off, which means that the spray we have meant to stay on the leaf, ends up in the ground below. By producing these larger droplets, the spray machine is delivering more material (expressed in gallons per minute) which is not only inefficient, but costly.
Your Nozzles can begin to show wear after only 10 hours of use at 100 psi.
The illustrations represents three common conditions on a spray boom. The symbol CV means Coefficient of Variation. A lower CV percentage means a more uniform distribution.
To illustrate the importance of spraying with good nozzles, take the following equation:
If your nozzle orifices are showing a wear of 10% (and this is the point that most manufacturers recommend replacement) and your spray costs are $35.00 per acre, you are wasting $3.50 per acre in excess spray.
Project that to 500 acres and you are looking at a loss of $1,750.00. Now, consider that nozzle replacement would generally run you between 100 and 300 dollars, it would pay to replace your nozzles promptly, with the added bonus that you would not have to worry about poor coverage or misapplication, since having fresh nozzles would keep your machine calibrated and efficient.
Remember always replace all nozzles, not just the ones you think are worn. Another consideration to these economics is to upgrade the type of nozzle you are using to one of the newer and more durable materials. These nozzles are considerably more expensive, but also offer a much longer wear life. This alone, more than justifies the extra expense.
Originally, nozzles were mostly manufactured in brass, mainly because brass is a soft metal and it was easy to accurately machine the orifices with the existing techniques. However, because brass is a soft metal, the wear life of a brass spray tip is relatively short, especially at high pressures, and does not justify its cost.
As the metalworking technology advanced, spray tip manufacturers introduced nozzles in Stainless Steel and Hardened Stainless Steel. These tips were considerably superior in wear life to their brass predecessors and available in most styles of nozzles:
- Flat fan
- Hollow and full cones
- Solid streams
- Off-center
- Even fans
- Narrow angle
- Etc.
Because these nozzles cost up to 5 times more than their brass counterparts, growers continued with the more economic tips for two reasons:
- They were seldom told by the seller of the advantages of the longer lasting hardened tips
- They did not realize how nozzle wear would affect their coverage and application patterns.
Of course, the advantage is with Hardened Stainless Steel, as it lasts some 8 to 14 times longer than brass, whereas regular Stainless Steel will last from 3 to 5 times more than brass, which cost-wise makes it a trade-off.
In the mid-eighties, manufacturers introduced some of their nozzles in plastic. Plastic being a very economical material and easy to mold or machine, gave growers a very economical tip with extended wear because the smooth surface of the plastic reduced the effects of the abrasive components found in agricultural chemicals.
Not all nozzle types were produced in plastic and most were recommended for low pressure applications. Some plastic nozzles are still in production and are know as Polymer Nozzles. Their wear life averages 4 to 6 times that of brass nozzles, at approximately the same cost.
One disadvantage is the fact that they are delicate and can be easily damaged under normal use and require constant monitoring to assure proper calibration and pattern.
Technological advances in the late eighties made it possible to accurately produce spray tips in Ceramic. We have to thank NASA and the Space Program for this development because the the first mass produced ceramic spray nozzles were introduced by the same group that supplies the ceramic tiles that protect the Space Shuttle on re-entry.
Ceramic is an extremely hard material and nozzles are either machined or molded, depending on the manufacturer and process. Ceramic nozzles assure a much greater wear life value because they are not only harder, but the surfaces are considerably smoother than metal. Ceramic is also corrosive resistant to most chemicals used today.
Because of the complexity in their production, not all nozzle types used in agriculture are available at this time in ceramic.
However, most of the fan, hollow and solid cone and disc/core models are available from the different manufacturers and gaining rapid acceptance with most forward-thinking growers. Cost wise, ceramic nozzles in general run about 25% more than Hardened Stainless Steel, but last between 90 and 200 times more than brass nozzles.
But ceramic nozzles must be handled with utmost care and mounted with nylon strainers as excessive torque when tightening or rough handling can crack or damage them very easily. Even so, their advantages far outdo any other nozzle material and would make them the clear choice for efficient and economical operation of your spray rigs.
There are several other materials used in spray nozzles, but mainly limited to specialty applications. The following are the most current and I show their wear ratio compared to their brass counterparts as a number after their name:
- Aluminum: 1
- Monel: 3
- Hastelloy: 6
- Stellite: 15
- Silicon Carbide: 90
- Carbides: 180
The above is not included in the analysis because of their high cost to wear ratio.
At this point you are going to wonder which nozzle material is best for you.
Consider abrasion as the major factor and pressure as its partner in crime. The higher your operating pressure, the more abrasion your nozzles will be subjected to. Therefore it seems logical that a rule of thumb would be to use ceramic nozzles in high pressure situations. Because of their orifice design and durability, you will get optimum performance with ceramics at pressures over 100 psi.
You have more of a choice if you are applying herbicides (20-30psi) or spraying at lower pressures: (40-60psi). Polymer (plastic) nozzles do very well with herbicides, especially when using the “drift control” type nozzles.
For field or banding at 40-60psi I would recommend hardened stainless steel disc/core and fan type nozzles, but ceramic hollow or solid cone nozzles.
The disc/core tips in ceramic do not seem to produce a uniform pattern at lower pressures. This could be due to the depth of the orifice of almost 3/32″ which gives the spray a tunneling effect which, at those low pressures, contributes to producing larger droplets in the pattern than the equivalent hardened stainless steel disc/core tips in which the orifice has a depth of only 1/64″.
The bottom line of this conversation is the fact that many growers until now have not paid that much attention to calibration and proper care of their spray tips, which should now become a priority, not only from the economical point of view, but also as a tool to prevent excessive waste and contamination.
Feeding Plants Using Foliage Fertilizer Applications
December 31, 2007
Most of our basic growing methods rely on ground fertilizer applications to give plants the nutrients needed for healthy development. However, at one time or another we may have tried applying nutrients to correct deficiencies or accelerate growth (“green up” our plants), with mixed results.
Those “mixed results” may be because in order for the plants to absorb the foliar applied elements, we have to understand how they work in order to apply them effectively.
If we just spray them on at random, chances are that we are just throwing our money and effort away, so here are a few basic points that will help us to get the foliar micronutrients to work.
Macro vs. Micro:
Macronutrients (N,P,K, calcium, magnesium and sulphur) must be applied on the ground as the plant requirements are higher than what could be supplied through the foliage. They are also difficult to absorb through leaf tissues.
Micronutrients (including zinc, boron, copper, iron, manganese, molybdenum, etc) are usually required in small amounts and can be applied through foliage as you can normally cover the plant’s needs with two or three annual applications.
However, for the leaves to absorb them, they must be produced in a foliar spray version, which usually means that at least the zinc and the iron are chelated.
Foliar Fertilizer Application:
One of the reasons for foliar application of micronutrients is that in soils with pH over 7.5 most micronutrients become unavailable and therefore practically useless.
If you have alkaline soils, don’t waste your time putting down micros with the exception of moly, which seems to be unaffected. If you want to adjust the soil pH, bring it down to the ideal at 6.5.
Another consideration is the possible phytotoxicity of the material being sprayed and this is dependent on the concentration of the product and the ambient temperatures affecting the crops. At times, the required concentrations are too high to apply as they will cause leaf burn, and so to be able to cover the nutritional needs of the plants, you will have to make several applications.
Do the math and decide if this is for you.
Leaf Uptake:
Leaf absorption (uptake) is critical for foliar feeds to work and this changes with each variety of plants. Check with your university or extension agent on the intake properties of the plants you grow.
Speaking of leaves, remember that many of them are not designed for liquid nutrient solution uptake, and that, in general only about 15 to 20% of the materials actually are taken in.
The stomates, through which absorption takes place, are found mainly on the undersides of the leaves. The upper surfaces of the leaves are usually coated with waxy substances, which protect that stoma from the elements. As the leaf ages, this cuticle becomes thicker. Also, the hotter the climate, the heavier the cuticle.
However, don’t confuse the hot climate with the ideal times for absorption, which are usually in mid morning when the cuticles are still soft from the overnight humidity and the leaf metabolism is active because of the warm temperature.
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Intelligent Spraying Equipment – What do Space Programs Have to do With Technology in Agriculture?
December 30, 2007
Intelligent Spraying Equipment can now use GPS (Global Positioning System) to detect and locate different soil conditions in large fields, and is a by-product of the guidance and probing systems developed for the space program.
Now look at Sonar and Laser technology being applied to sprayers to detect the targets and direct the spray specifically at the plants and trees that have to be treated, rather than just blowing a continuous cloud of spray into the air: it comes from military targeting systems developed over the years and fully proven in the Gulf War.
Yes, there are sprayers on the market and presently in use by progressive growers that actually look at the plant and turn on the nozzles according to the shape and position of that plant. They are even so smart that you can program them to open a little before and close a little later to compensate for wind conditions!
Get used to names like "Smart-Spray", "Tree-See" and "Tree-Sense". They are all presently available and can be even retro-fitted to most of the existing air-blast machines.
How do they work? At present there are two systems:
The Laser "Tree-Sense" offered by AgTech. This is a three dimensional image range sensor originally designed for imaging enemy tanks in Desert Storm.
With a single scanner, mounted in the front of the sprayer, it can map the image of a tree up to 100 feet away on either side of the sprayer.
In doing this, it feeds the size, height and location into the onboard computer. Eight inches before the leading edge of the tree, the computer opens the necessary sprayer orifices to totally spray the tree and shuts them off eight inches after the trailing edge. The spaces in between are not sprayed.
The nozzles are controlled by electric solenoid valves which are set up in zones so that only the foliage detected by the scanner is sprayed. This system can be retrofitted to Agtec Sprayers with standard orchard heads.
The "Sonar" or ultrasonic system was invented by Bert Roper as the "Tree-See", in 1982, and has been selling in Florida since the first unit was purchased by Coca Cola Foods in 1984.
It is now offered as the "Smart Spray" by Durand Wayland and as a retrofit for existing, FMC, Durand Wayland, Aero Fan and other major brands of air blast sprayers by its developer, Roper Growers Coop. of Winter Garden, FL.
The Sonar system uses ultrasonic impulses to detect the presence or absence of trees and plants. This detection is done by sensors installed on each side of the sprayer that can be aimed in any desired direction to cover optimum zones, according to the crop being sprayed.
The models range from a one sensor (small tree) unit to a ten sensor model (five sensors per side) that can cover trees up to 40 ft high and is usually recommended for Towers and Oscillators. These sensors have a range of 25 feet so as not to detect targets over in the next row. Tree-See systems can also be used on fertilizer spreaders (both dry and liquid) and herbicide applicators.
The Tree-See/SmartSpray systems can be programmed to open earlier or close later, according to wind and drift conditions. The valves are controlled by pneumatic (compressed air) systems that give instant response with higher line pressures and are more durable to extended heavy cycling situations, such as close tree spacing typical of Florida.
Of course, the valves have to be told what to do and that is done by individual zone controllers on the Roper Tree-See and a computer on the Smart-Spray.
The Sprayer wheels are also sending information to the processors so that one can have data on area sprayed, GPAs, material saved vs conventional systems. The Smart Spray even has a reset program for citrus that tells the sprayer not to spray when passing mature trees.
This gives operators that ability to work an entire grove while spraying only smaller trees and resets. A hand held console allows the operator to program the machine according to what is going to be sprayed. This console also stores information and gives data on coverage, efficiency, etc., that can be used for pesticide application records.
What does all this mean?
Imagine a grove with about 30% resets. A conventional sprayer would be spraying the entire property with all of its nozzles on, except when the operator gets to the end of the row (if he remembers to turn them off or disconnect the PTO).
One of these Tree-See/Tree-Sense/Smart-Spray machines would detect the open spaces and absence of full size trees and only open the nozzles necessary to cover the resets, and not spray in the open spaces. Estimated savings: 30 to 40% — You figure the dollars saved. The rest of us will benefit from the reduced air pollution.
There are dramatic savings in spray materials to be realized on young groves as well as new plantings. The trees occupy a fraction of the air space in the rows and these imaging systems can produce savings of up to 70% over conventional blowers in these situations.
Of course, as the trees grow, they begin to fill the empty spaces and the savings become less dramatic. However, in most mature groves, there are always empty spaces, resets and the general non-uniformity of the canopies, where savings can be realized with these "intelligent sprayers".
My direct experience has been with Durand Wayland’s Smart Sprayers in two different tropical fruit operations, where I have found them to be more than worth the extra initial cost and, despite my initial fears, extremely dependable.
Down time has been minimal, considering the complexity of the system and parts availability and technical support is very good. Both growers have used the machines for over two years and practically on a daily basis in tropical conditions, mainly on Mangoes , Avocados and some citrus.
The actual savings have ranged from 60% in young groves (1 year old mangoes) to 18% in topped and hedged 5 year mangoes. Avocados have reported ranges of 15 to 30% in mature groves. Citrus (Limes) has varied between 15 and 35% – depending on the amount of resets in the field.
The manufacturers publish charts showing how the savings using these systems can return their cost in either one year or two, depending on the total amount of acres sprayed and based on average chemical reductions of 30%. The best way to calculate this is to use your own figures and consider that the costs of these systems add an average of 15,000.00 dollars to the cost of a full size blower (500 to 1000 gallons).
So, in essence, your exercise should go something like this:
Number of Acres Sprayed X Chemical Cost per Acre X .2 = Savings
And I put a multiplier of .2 to represent 20% and not 30% in savings, just to be conservative. To adapt this calculation to your actual situation you can use the following multipliers: New Plantings: .55 (55%) Young Trees: .45 (45%) Mature Trees: .15 (15%) Average: .20 (20%)
So if you spray 500 acres of young trees at 100 dollars per acre, your savings would be: 500 x 100 = 50,000.00 x .45 = 22,500.00
As you can see, these systems could produce important savings for your operation. In addition, the Roper system has been adapted to dry fertilizer spreaders, specifically for treating young trees and accurate placement. The advantage over conventional wheel driven systems is that it does not get out of "sync" with the plantings as it places the dose of material where the sensor has actually seen the target area.
These systems are also applied to herbicide applicators mainly to work with the outboard nozzle, which they will shut off when the sensor detects a tree or planting that should not be sprayed. Both the fertilizer applicator and herbicide systems are considerably less expensive and operate usually with only one sensor and can run in the $2000.00 range.
For additional information regarding specific systems and retro-fitting, contact:
AgTech Crop Sprayers
800-704-4292
Roper Growers Co-operative
800-872-5032
Durand Wayland Inc
800-241-2308
Chemical Containers Inc
800-346-7867
Greenhouse Watering Systems Boom Irrigation – Apply Water/Chemicals Solutions More Efficiently
December 30, 2007
The effective, efficient delivery of water/chemical solutions to greenhouse crops is of paramount importance in successfully producing a greenhouse crop.
Water is effectively delivered when it is applied in a timely fashion and uniformly applied in proper amounts. Compromising on any of the above could unnecessarily stress the greenhouse crop and result in reduced plant vigor, increased mortality and lower a crops marketability.
One of the most efficient methods of effectively delivering water to plants is via an overhead boom irrigator. With. a series of nozzles spaced across a length of pipe, the resulting band of water these nozzles apply is remarkably uniform.
Due to this uniformity, booms are able to apply water/chemical solutions far more efficiently than fixed sprinkler systems. When coupled to a motorized carrier riding on some form of track system, it truly becomes a low cost means of irrigating large areas in a relatively short time period. Booms that have been in operation for over 10 years are not uncommon.
There are two types of watering booms: Wet and Dry
A boom is considered a wet boom if the pipe span is not only used as a support mechanism for the spray nozzles but delivers the water to them as well, hence the name WET BOOM.
A boom that is used merely as a span along which to space the nozzles, but not deliver any water, is considered a DRY BOOM.
The water/chemical solution is delivered to the nozzles via a separate hose line which runs along the boom span using it as a support mechanism by which to feed each nozzle. The Agronomic industry typically uses Dry Booms because the nozzle spacing can be altered to accommodate varying row crop spacing.
Since greenhouse space comes at a premium price, row cropping is not economically feasible. Therefore most booms used in the greenhouse are typically Wet booms and the following discussion will focus on such a boom style.
In comparison to other watering methods, Boom irrigation may place a greater demand on your plumbing system. Booms typically span the width of the greenhouse and are capable of irrigating the entire width simultaneously or in portions depending upon how many valves the boom is equipped with.
Determining water flow requirements for a boom is a function of the # of nozzles the boom is to be equipped with, their G.P.M. output and the inner diameter of the pipe used to supply them. Typical spacing for nozzles is 14″ to 20″ inches.
Outputs run from 0.067gpm* for misting to 0.8 gpm for watering bedding plants or potted crops. *Nozzle outputs are based upon 40 psi operating pressure. The standard pipe size is 1″ id.
Nozzle count is determined as follows:
(Boom length (in feet) x 12) minus aisle widths in inches (divided by nozzle spacing + 1) + edge Count* = nozzle count. *Properly designed booms take into account edge drying by doubling up the nozzles along edges of growing areas.
In some cases these nozzles are mounted on swivels so that a directional spray can be achieved along the edges. With the following information we can determine the maximum load a boom will place upon a plumbing system.
Example:
We have a 3 bay gutter connected greenhouse with bays 30′ wide and a center aisle 24″ wide down each bay. One bay is used to root cuttings, another for bedding plants and the third for potted crops.
We will equip our boom with a special three headed nozzle body, with a nozzle tip appropriate for each particular crop. Our tip sizes will be 0.067, 0.4 and 0.8 gpm. Since we are concerned with maximum loads the boom will place upon our plumbing system we only need to focus on the 0.8 gpm tips.
Our nozzle count is figured thusly: (30 x 12) – 24"aisle width (divided by 14" nozzle spacing + 1) + 4 edges. The result is a boom requiring a total of 29 nozzles. 29 x 0.8 =23.2 gpm demand on our plumbing system. 23.2 gallons per minute is well within the flow rate a 1 " id pipe is capable of supplying so we know that, should we choose, we can irrigate the entire greenhouse width simultaneously.
Controlling nozzle output is only one means by which a boom irrigator can control the amount of moisture it applies. A very important second feature of boom irrigators is their ability to move. A well designed boom irrigator will have a D.C. motor affording variable speed adjustment.
By controlling the travel speed, a grower can deliver precisely the amount of moisture a crop requires and to whatever particular depth desired. Typical speeds range from 3.5 to 70 feet per minute.
Knowing how much water a boom can apply and at what speeds it is capable of moving provides the foundation necessary to answer the following question.
The question is: How much square footage can we expect a boom to irrigate?
This requires knowing the daily moisture requirements of the greenhouse crop. With geographical differences (solar and thermal differences), microclimate differences ranging from the amount of horizontal air flow to soilless mix used, not to mention differences between crops, it becomes a question with as many answers as there are different greenhouses. Typical ranges are anywhere from 10,000 to 20,000 square feet per boom irrigator.
Naturally most greenhouses do not contain 20,000 sq. ft. under a single roof. To irrigate this much area requires a boom designed with an ability to be transferred. Depending on the design of the boom irrigator, this transfer can be from bay to bay or house to house. This is accomplished by means of overhead track systems which allow the machine to be moved to the next area in need of irrigation.
These types of overhead track systems are very similar to ones seen in the dry cleaning industry. With gutter connected houses the machine is usually moved from bay to bay along the end wall.
At each bay a switch is provided to allow the machine to move off the transfer track and down into the bay or continue down the transfer track to the next bay. With free standing quonsets, the machine is moved out the end wall door onto an overhead track running along the outside from house to house. Some boom manufacturers provide booms that pivot allowing them to exit through normal size door widths.
The level of control features now available in boom irrigators runs from simplistic to state of the art. The basic package includes a boom drive system equipped with variable speed and a simple timing mechanism to start the boom irrigator at a particular time of day. More sophisticated controls allow a machine to hold many watering programs each with their own start, stop, multiple pass and repeat time intervals.
Where crop changes occur on the bench they can speed up or slow down to change the water output. The booms can turn the water off where aisles or blank spots on the bench occur and turn the water back on where the bench is full. Some are able to be remote started via environmental computers or devices that measure solar load.
Although booms are capable of watering a crop more effectively and efficiently than most other methods and do so year in and year out with only one paycheck, it is just as important to have a system you can depend upon. Well designed boom irrigators have safety features built in to insure no damage occurs to the crop they are entrusted to irrigate. Several common safety features are:
- A collision feature that turns the machine travel and water off if it should collide with some obstruction.
- A low water pressure shutoff feature that stops the machine and turns the water off if it drops below a substandard pressure level. It then waits until the pressure is regained before resuming.
- A water shut-off feature should a power loss occur
- Some booms are able to utilize the phone line to call you during off hours should some problem occur. Additionally well designed booms will incorporate modular construction to afford easy change out of parts in the field.
Booms provide growers with a means of increasing their profit margin. Typical boom systems purchased provide a payback period for their new owners within the first year of use. This is accomplished in many ways.
Their more efficient use of water/chemical solutions compared to hand watering or fixed sprinkler systems.
- The consistent uniformity of application.
- The timeliness of applying the solution.
- Enhanced rooting of cuttings and germination of plugs.
- The ability to reduce or eliminate access aisles formerly needed to hand water and replace with income generating crop.
- The fact that booms work without requiring a paycheck.
Understanding Phytotoxicity and Plants
December 30, 2007
Growers are routinely applying a wide variety of materials as foliar sprays for pest control, nutritional supplementation, or a variety of other purposes. We know the benefits of these materials, but there is a general lack of information concerning phytotoxicity.
The term phytotoxicity is roughly equivalent to spray injury. We have probably all applied sprays at one time or another that inadvertently resulted in plant injury in contrast to a positive response and many times we don’t know exactly why it occurred, and therefore do not know what we can do to prevent it in the future.
Often, a grower will apply a particular spray mixture on a regular basis without incident; then suddenly the same mixture results in injury. There are several different types of phytotoxicity. The names of these types of spray injury are my own, as I have not seen this subject formally referred to in the published literature.
Phototoxicity
- Fundamental
- Overload
- Cumulative
- Combination
- Placement
- Episodic
Fundamental Phototoxicity
Is simply when a plant variety is sensitive to a particular chemical. Examples would be the sensitivity of Aralia to Vydate or Hibiscus to Malathion. There are simply situations where a plant and a chemical just don’t get along. The activity of selective herbicides can also fall under the category of Fundamental Phytotoxicity.
Overload Phototoxicity
A second type of phytotoxicity I have identified, where an excessive rate of a chemical that is otherwise safe, is applied, and therefore causes injury.
You may also cause Overload Phytotoxicity by mixing too many elements in your spray tank. I have seen growers mix six or eight different chemicals in a tank, all at proper and safe rates. By themselves, these materials should not cause phytotoxicity. Bear in mind however, anytime you mix three or four different materials in a spray tank, the potential for Overload Phytotoxicity increases.
Cumulative Phototoxicity
When individual applications are not the problem, but that phytotoxicity occurs via build-up from regular applications of the same type. I have seen Spathiphyllum sprayed regularly with iron to the point of inducing iron toxicity. And while individual applications of Subdue fungicide may not cause a problem, applied too many times in succession, and at too close an interval, phytotoxicity can occur.
Combination Phototoxicity
This occurs when a chemical or set of chemicals may be applied without injury, but when mixed with incompatible material, results in crop injury.
For example, Daconil and Vendex are safe by themselves on numerous crops, but, when you mix them together, which you should not do, the risk of spray injury is great. Aliette mixed with copper fungicides also presents great risks, whereas individually the materials are quite safe.
Placement Phototoxicity
A somewhat rare type of phytotoxicity, which occurs when a material applied in the correct fashion is perfectly safe, but is placed where it shouldn’t. A good example would be applying Ronstar to a soil for preemergent weed control. That in itself is normally very safe, but if the Ronstar granules end up in the whorl of a sensitive plant phytotoxicity can damage that plant.
Episodic Phototoxicity
This refers to an episode where a common spray, for some unknown reason, and where it has never occurred before, suddenly causes plant injury. Usually in this type of situation weather conditions are a factor. Some sprays are safe in cooler weather whereas they can become very dangerous in high heat conditions.
Water-stressed plants can be very sensitive to otherwise safe spray applications. Improper cleaning of the spray tank from a previous application can cause Episodic Phytotoxicity. Sometimes, the causes of Episodic Phytotoxicity remain unknown.
Preventing Phototoxicity
What can a grower do to prevent all these potential problems?
First, it is important to note that phytotoxicity is a relatively rare event, occurring perhaps only once in every 500 applications on average.
To reduce those odds even more, the rules are simple:
- Clean your spray tank thoroughly between each application
- Use a separate, and marked accordingly, sprayer for herbicides only
- Watch your application rates carefully, and try not to mix more than three or four items in the tank
- Do not apply a tank mix unless your experience or chemical labels indicate a mixture is safe
- Read the chemical labels
- Don’t spray in excessive heat, or when plants are stressed or wilted
- Finally, when you are unsure about a spray mixture, there are a number of sources for useful information you can tap into, such as consultants, extension agents, other growers, chemical companies, ag sales people or the Internet
If you pay attention to what you are doing regarding the application of agricultural sprays and are reasonably diligent, phytotoxicity can be avoided almost all of the time.
Author: Lynn Griffith – President of A & L Southern Agricultural Laboratories
Nutrients – The Mechanism of Foliar Absorption of Nutrients is Not Well Understood
December 30, 2007
Plants absorb nutrients as well as other chemicals through their foliage to varying degrees. Growers in most all types of agriculture apply foliar nutritional sprays from time to time for various reasons.
A basic philosophy many growers utilize is to apply what is believed to be required to the soil in the fertilization program, and use nutritional foliar supplements as a tool to give crops any nutrients they may still be lacking. Even though growers constantly use this technique as nutritional supplement, the mechanism of foliar absorption of nutrients is not well understood.
In order to understand foliar absorption, we must first take a look at the surface of a leaf. Moving from the outside. The leaf surface is composed of layers of cuticular wax, followed by the cuticle or “skin” of the leaf. The cuticle exudes the wax. Under the cuticle are the cell walls of various types of leaf cells. Inside the cell walls are the plasma membranes of the cells themselves.
A foliar applied nutrient must pass through the cuticular wax, the cuticle, the cell wall, and the membrane in that order. Sometimes the nutrient will pass through these various layers, while other times it may pass through the spaces between these layers. Such absorption involves both active and passive processes of the leaf.
The second and most often the, major means of foliar absorption is through the stomates, which are microscopic pores in the epidermis of the leaf. When the stomates are open, foliar absorption is often easier. Plant species vary widely in the, number of stomates per leaf area, and in their relative distribution.
Some plants have more stomates on the lower leaf surface than on the upper and some vice versa.
In simpler terms, some plants are, good at absorbing nutrients through their leaves, while others are not. The variables tend to be how many stomates and how they are distributed, and how thick the waxy cuticle of the leaf is.
Plants with large, broad soft leaves such as Spathiphyllum or many bedding plant species are rather efficient at absorbing, foliar nutrients. Palms, Avocados, Cucurbits, some Citrus and Zamias for example are not as adept at this absorption, due to the thicker tougher nature of their foliage.
The speed of absorption of nutrients is quite variable according to the nutrient, and to some degree the plant type. Rates of foliar absorption have generally not been studied in ornamental varieties.
One Thing Not Widely Known is that Nutrients are Generally ONLY ABSORBED while the spray is wet on the Leaf!
Once the spray has dried, absorption generally ceases until the leaves are moistened again, either by the dew the next day or additional rainfall or overhead irrigation. The various types of chelating agents are also not equal in their ability to penetrate the leaf. Some chelating agents work better on some types of plants, but not necessarily as well on others. The best chelating agent will depend in part on what type of plant you are spraying.
Another Common Misconception Regards Rates of Foliar Nutritional Applications.
Generally, there is a great deal of difference between the amount of chemical it takes to maximize absorption and the amount it takes to burn. Absorption is the limiting factor, so don’t make your rates too high. You may be able to double or triple the spray rate, but it won’t necessary increase absorption. It will increase risk of spray injury, so be conservative in your foliar application rates.
There are a number of situations when foliar nutritional supplements are especially useful. One is during propagation of slow rooting plant material. Long term mist propagation can leach nutrients severely, and foliar nutritional sprays during that time are very helpful. Nutritional sprays can be used efficiently to overcome other problems.
Another useful foliar technique is during cold fronts. When a cold front comes down, frequently you get heavy rain followed by several cold days. During this period, the fertilizer is not releasing a great deal, and the plants are not feeding. That is a good time to come in and apply some foliar nutrition to keep the plants moving until things warm up.
Several Techniques should be Used When Trying to Maximize Foliar Absorption of Nutrients.
One is to try to maximize the time that the spray is wet on the foliage. This preferably means early in the morning, when humidity is up, leaves are wet with dew. Spraying in the middle of a hot day will give you reduced effectiveness in absorption. It also helps to add urea or potassium nitrate to nutritional sprays when applying trace elements.
The mechanism is not known, but there is substantial research that indicates applying these materials with trace, elements increases trace element absorption. Try to spray when the stomates are open, preferably during a cooler time of day. Some industries like to spray at night, and that can be useful in some situations.
Try also to coat both the upper and lower leaf surfaces where practical, as many times the spray stays wet on the leaf longer, and there are more stomates to facilitate absorption on the lower leaf surfaces of many plant varieties.
The use of wetting agents or surfactants also aids in absorption, by spreading out the spray from droplets into a broader shape, increasing contact with the foliage. Surfactants also reduce the angle at which the spray material enters the leaf, which can be useful. It is generally useful to thoroughly wet the foliage when applying nutritional sprays.
Low volume sprayers may not be as effective in some cases. You should spray to run off, and once again cover the lower leaf surfaces.
Finally, do not get too high on your rates. Going higher on the rates of chemicals applied can actually reduce absorption, as can mixing too many nutritionals in the tank at a time.
Foliar nutritional sprays can be a very useful technique, especially when you understand the principles behind it. Nutritional sprays enable you to correct deficiencies, strengthen weak or damaged crops, speed growth and overall grow better plants, which is of course, the bottom line.
