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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TYLCV - Tomato Yellow Leaf Curl Virus
December 31, 2007
TYLCV causes more severe symptoms and greater yield losses than Tomato Mottle Virus (ToMoV). It takes an estimated 15-30 minutes of SWF feeding to inoculate a plant. The SWF retains the virus, for several weeks. Symptoms will be visible in tomato in approximately 2-3 weeks after infection, a little longer than ToMoV.
Leaf symptoms include chlorotic margins, small leaves which are cupped, thick and rubbery. Tops of infected plants may took like a head of broccoli. The majority (up to 90%) of flowers abscise after infection, thus few fruit is produced. (TYLCV is very similar in its effects Bean Golden Mosaic Virus in that if young plants are affected, it is highly likely that fruit will not set).
TYLCV can affect more hosts than ToMoV, although crop plants are not considered with the exception of tobacco, which, like many of the weed hosts, do not show symptoms.
In Israel, weed hosts bridge the gap between tomato seasons. In the Dominican Republic, there is a government enforced whitefly free period. In Florida, we do not yet know the extent that weeds are a host, as many of our weeds do not grow in some of the countries where TYLCV is found.
This virus is not seed or mechanically transmitted. Whitefly transmission, however, is more efficient than for ToMoV. In greenhouse tests, 15 SWF were required for transmission, compared to 40 from ToMoV. Individual insects transmitted at 30-40%, compared to 5-10% for ToMoV.
Recommendations For Management
- Keep whitefly populations low especially in the first half of the season
- Use Admire in the transplants as soon as possible
- Use chemical control on all plantings of tomato and continue through final harvest and u-pick
- Isolate cherry tomato fields from large fruited plantings
- Delay fall plantings as much as is economically possible
- Learn to identify early symptoms of TYLCV and rogue Infected plants as soon as infections are identified throughout the season
- Pull plant from the bed and place in plastic bag at site, tie shut to prevent spread of any whiteflies to other plants, and discard in trash
- Plow under fields immediately after harvest to reduce whitefly populations and virus carry-over to the spring tomato crop and to other crops which are good hosts for whiteflies, and use the best sanitation practices
- Destroy volunteer tomato plants in and around fields
Separate plantings of tomatoes in time and space from plantings of crop hosts which are good sources of whiteflies (ie. cabbage, cucurbits, potato) - UV-reflective mulches will reduce landing of whitefties in your field and will help reduce incidence of both aphid and whitefly borne viruses including TYLCV.
- Destroy tomato volunteers throughout the season
- Delay spring plantings as long as is possible
- Use WF and virus free transplants
TYLCV Characteristics
- Leaf symptoms: Chlorotic margins, leaves very small and cupped, thick and rubbery
- Plant symptoms: Stunting, more severe than that caused by ToMoV, like ToMoV, severity increases the younger the plant at infection; tops may look like broccoli
- Fruit symptoms: Majority of flowers abscise after infection, few fruits produced
- Host range: Broad
- Weed hosts: Unknown, but likely
- Whitefty transmission efficiency: In greenhouse tests 15 insects for 100% transmission; individual insects transmitted at 30-40%
- Seed transmission: No
- Mechanical transmission: Not under normal conditions
Rears 500 Gallon Powerblast Standard Orchard Sprayer
December 30, 2007
After testing a new Rears 500 Gallon Powerblast Standard orchard sprayer I can say I am really impressed by the performance and features of this machine.
The 28 degree fan gives a tremendous volume of air at relatively slow speed, which gives the air blast considerable inertia and is able to penetrate thick canopies without really damaging fruit or even blooms.
This is important, because canopy penetration is not a question of high speed, but being able to displace the air that is already in place, so that the air with the spray particles can move them into the canopy and deposit them on the leaves. I usually relate the canno type sprayers to trying to sweep the patio with a toothbrush!
Very impressive in initial airspeed out of the tiny cannon opening, but no weight, mass and punch to follow through!
Anyway, aside from the excellent air volume, the Rears machine is equipped with Hu valves, which work on a by-pass differential pressure system which is very ingenious and quite efficient, that, added to the electric manifold controls, make running this unit a pleasure.
Another feature that caught my fancy is the Constant Velocity Hitch, which allows you to make tight turns (the ends of the the rows are always too tight!) without damaging the driveshaft and without having to turn off the PTO.
This hitch operates off the lower arms of the three point hitch and the driveshaft is comprised of 3 equally long sections, so that there is no sliding in and out of the telescoping standard shaft.
Our Rating on a scale from 1 to 10 : 8 1/2
Stay tuned; we are currently testing other units and innovative spray systems.
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.
Posting Spray Application Information in a Central Location - Worker Protection Safety
December 30, 2007
Spray application information must be posted in a central location after the spraying is done.
True or False?
Answer: FALSE
The WPS (Worker Protection Standards) requires that the information be posted before the spraying begins. This is to inform employees as to what areas will be sprayed and must be avoided.
The information posted must include:
- Location and description of the area to be treated.
- The product name, EPA registration number and active ingredient(s) of the pesticide
- The time and date the pesticide is scheduled to be applied
- The restricted entry interval (REI) for the pesticide.
This information must be available for 30 days AFTER the REI interval (Re Entry Interval) for the pesticide has expired.
Other information the central location must have:
- The name, telephone number and address of the nearest medical facility
- The WPS Pesticide Safety Poster in good, readable condition.
Approved Eyewash Solutions - Worker Protection
December 30, 2007
Can ONLY approved eyewash solutions can be used in rinsing eyes contaminated with pesticides?
True or False?
Answer: FALSE
Clear, clean water is more than adequate for flushing and rinsing eyes that have been affected by pesticides. Published recommendations are that the flushing with water or other eyewash solutions be continuous for up to 15 minutes to assure total removal of residues of chemicals.
The water should be clean and clear, preferably potable and should not be too warm or excessively cold. (One of the approved EPA WPS (worker protection standards) Training tapes shows an instructor demonstrating how to flush a worker’s eyes out with water from an Igloo cooler, which hopefully was not ice water).
Specialized eyewash solutions must be current and fresh. We have a tendency to set-up eyewash stations and then let them sit unattended for long periods (sometimes years) and then, when we need to use the solution, it has decomposed and smells of sewer water!. This is not good for the eyes! The eyewash solutions should be replaced every 6 months and more frequently if the station is out in direct sunlight.
Posting Spray Records - Worker Protection Safety
December 30, 2007
Spray records posted in the “Central Location” to inform workers of applications should have the same information as the records kept by the licensed applicator as required by law.
True or False?
Answer: FALSE
The Worker Protection Standard requires that the data posted in the “Central Location” to inform workers of spray applications contain the following items:
- Date and time of application
- Location sprayed
- Product(s) applied
- EPA numbers
- Active ingredients
- Reentry period
- Date and time it will be safe to enter the area
These sheets must be kept posted for 30 days.
Spray records required of the applicators must contain the following data:
- Date
- Location
- Size of area treated
- Crop(s)
- Product(s) applied
- EPA Numbers
- Active ingredients
- Formulation X 100 gallons
- Total gallons used
- Method of application
- Name of applicator
- Name of licensee
- REI
- PPE used
- Posting requirements
These records, signed by the applicator or supervisor, must be kept on file for 2 years.
