Institute of Food and Agricultural Sciences
2000 Florida Postharvest Horticulture Institute
& Industry Tour - March 6-10, 2000
Institute-March 6th, University of Florida, Gainesville, with video-links to several sites in Florida.
Industry Tour-March 7-10th Statewide
For more information contact:
Steve Sargent or Abbie Fox, (352)392-1928,
For the Immokalee site, contact Gene McAvoy 941-674-4092
Aquatic Weed Control, Aquatic Plant Culture
and Revegetation Short Course - May 15-19, 2000
Fort Lauderdale, Florida. Earn up to 24 CEUs.
For more information contact: Beth Miller-Tipton at (352)392-5930,
fax (352)392-9734 or e-mail: firstname.lastname@example.org.
Visit the workshop web site at: http://www.ifas.ufl.edu/~conferweb/
Selection & Management of Cover Crops in
Vegtable Production - March 15, 2000
Southwest Florida Research and Education Center, Immokalee - 11:00 am to 12:00 pm
Contact Gene McAvoy 941-674-4092 for more information.
Vegetable Growers Meeting - Spring Vegetable
Diseases - March 22, 2000 5:30 pm to 7:30 pm
Southwest Florida Research and Education Center, Immokalee - 11:00 am to
Contact Gene McAvoy 941-674-4092 for more information.
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Vegetable Extension Agent II
Hendry County Extension Office
PO Box 68
LaBelle, Florida, 33975
Vegetable production sure is a crazy business, when you stop to think about it. Tomato yields have been phenomenal and quality superb this season and yet prices are in the dumper. Is there any other industry, in which the producers are as economically penalized for increases in efficiency and output, such as occurs in the agriculture sector?
Fortunately overall prices for other vegetables have been somewhat stronger this year and those growers are doing all right.
Experienced growers are well aware of the cyclic nature of the industry and in the past one good season has often been sufficient to negate several poor ones. Unfortunately, the industry is changing and the costs of production have become so high that it is now difficult for even the most financial secure firms to weather the overwhelming losses that can accrue with the long stretch of low prices that have endured this season.
Although it may be of little solace at present, UF/IFAS economist John Van Sickle predicts that long term growth in demand for vegetables will be good news for Florida growers in coming years. God bless the farmer.
On other fronts.... With the methyl bromide clock ticking away, it is certainly encouraging that some workable alternatives are emerging. A recent field demonstration held at SWFREC, spot-lighted a promising piece of equipment that Dow is working with for the broadcast application of Telone. This rig offers a number of advantages and while Telone is not a 100% substitute for methyl bromide, this technology certainly looks like one of the promising alternatives available to growers.
What is still lacking in the whole equation is still good effective weed control materials especially in crops other than tomato. This is certainly a challenge for the research community as well as chemical companies. Hopefully - workable solutions will be forth coming in the near future.
Donít forget FQPA! The EPA is not resting on this one. Despite a slow start a whole slew of chemicals are currently under review - make it your business to keep up with what's going on here. If you donít you may find out a critical pest control material has faded into oblivion with hardly a whimper.
The farm labor advocates are at it again! The highly biased portrayal of growers as exploiters of labor is reminiscent of the hey day of communism when history books were being rewritten by a small cliche with a secret agenda. Our industry really needs to join forces and present the other side of the story. Failure to due so may result in alienation of the American public and erosion of popular support for a strong US ag-sector.
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In order to understand foliar absorption, we must first take a look at the surface of a leaf. Moving from the outside in 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 tomato or many bedding plant species are rather efficient at absorbing foliar nutrients. Crucifers for example are not as adept in 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.
IS WETTER BETTER?
One thing that is 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 necessarily 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, temperatures are down, and foliage is wet with dew. Spraying in the middle of a hot day will give you reduced effectiveness in absorption. It 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.
WHEN TO APPLY
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 aid 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.
Spray Tips 12/31/99
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in Vegetable Crops
Plants vary in their sensitivity or tolerance to soluble salts in the soil solution. Crops which are the most sensitive include beans, carrots, strawberries and onions (threshold EC values around 1.0 dS/m). Moderately sensitive crops include pepper, corn, potatoes, cabbage, cucumber, and tomato (threshold EC 1.2-3.2). Moderately tolerant plants include beets and zucchini squash (threshold EC 4.0-4.7). (Knott's Handbook for Vegetable Growers, 4th edition).
Usually it is not the salts themselves that are toxic, but the reduction in water uptake. As the soluble salt concentration in the soil increases, plants have a harder time extracting water from the soil solution. Variables such as plant age, soil type and environmental conditions also affect salt sensitivity; thus, soluble salts become more critical under the hot, dry and windy conditions we have seen this spring.
Excess salts in irrigation water can contribute to the total salt problem, especially wells in coastal areas, or very deep wells which can be affected by saltwater intrusion under unusually dry conditions. Where poor quality irrigation water is used or where there is a field history of salt problems, low-salt index fertilizers are less likely to aggravate the problem.
Fertilizer rate and placement can affect soluble
salt problems which are then magnified under drought conditions.
Following recommended fertilizer guidelines and paying careful attention
to placement can minimize problems. In the absence of rainfall to
either dilute or leach fertilizer salts down past the root system, what
can be done? Typically, soluble salts are less of a problem with
drip irrigation systems because lower amounts of in-bed fertilizer are
used due to the ability to fertigate. In addition, with drip
irrigation the movement of soluble salt laden water is down and away from the plant. In seep or subsurface systems, the movement of water is upward, towards the highest point of the bed which is typically the plant hole. As water is evaporated from the soil surface around the plant, salts become more concentrated around the plant root system. For this reason, lowering the water table by pulling deeper ditches can be a double-edged sword. While some salts may move with the water as it drops lower in the bed or below, the salts that are left will concentrate as the soil dries. Conversely, raising the water table may also defeat the purpose as additional fertilizer salts will be solubilized.
A related problem that is often associated with high soluble salt levels is blossom end rot. Blossom end rot occurs when there is a lack of calcium in fruit tissue. Because calcium moves with water in the transpiration stream, anything which stresses roots and impedes water uptake will also limit calcium uptake, including too much water, too little water or high soluble salts.
Another problem that may be seen on tomatoes which
is also related to the weather is a phenomenon termed physiological leaf
roll. Under conditions which maximize photosynthesis (i.e. warm,
very sunny days), excess carbohydrates build up in leaf tissue and cause
the plants to become somewhat leathery, and leaves roll upward. Although
normally seen on older, lower leaves, in a few cases leaf roll has been
severe with the entire plant affected. This condition can be exacerbated
by excess fertilizer, high N
rates and also seems to be worse in plants that have undergone heavy pruning. Usually, it does not cause too much problem with yield and quality. One exception might be some sunburning of exposed fruit on severely affected plants.
It's hot, dry seasons like this one which can show just how efficient or inefficient your irrigation system is! An easy, inexpensive way to check your system before it becomes critical is to sign up for the NRCS Mobile Irrigation Lab (MIL). Following on-site evaluations of irrigation systems, MIL technicians work with owners or operators to develop irrigation water management plans tailored to their individual needs. To find out if this free service is available in your area or to sign up, contact your local NRCS office.
(P. Gilreath, Vegetarian 5/99)
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As the NOSB votes on the reviewed materials are available, results will be posted to the omri.org site. "This posting of the list to omri.org makes one of our most valuable tools easy to access and update," says Bill Wolf, president of the OMRI board of directors. "As organic agriculture and demand for certified organic product continues to grow, we want to make OMRI's services available through every possible avenue and appropriate technology."
The ďOMRI Brand Name Products List" represents
OMRI's recommendations and opinions regarding the acceptability or unacceptability
of products used in organic production, processing and handling.
Manufacturers apply to have their brand name products reviewed by OMRI's
technical staff, after which a review panel of leading experts from the
organic industry votes on a product's status. OMRI's standards were
developed after reviewing various governmental and certification standards;
OMRI's recommendations and opinions regarding use of any listed product do not necessarily coincide with
applicable governmental or organizational standards.
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Because water is one of the best carriers of pathogens, it must be treated (either chemically or physically) to prevent the accumulation of pathogens in the water and prevent cross-contamination of sound produce. Such treatments are not particularly effective at reducing pathogen levels already on the surface of produce; it is much more effective to prevent contamination in the first place. This means following Good Agricultural Practices regarding water quality, use of manure and municipal biosolids, harvesting practices, and worker, field and packing facility sanitation.
Although chlorine is currently the sanitizer of choice for most vegetable packinghouses, other chemicals have been approved by the EPA for contact with food products. This article will briefly list some of the approved antimicrobial chemicals and discuss advantages and disadvantages of using each.
Chlorine is currently the predominant method used by packinghouses to sanitize water systems. Although chlorine is available in three forms -sodium hypochlorite, calcium hypochlorite, or chlorine gas -it is the resulting hypochlorous acid (HOCI) that is primarily responsible for killing pathogens. Currently, IFAS recommends using 100 to 150 parts per million (ppm) of free chlorine with a water pH between 6.5 and 7.5.
The main advantages to using chlorine are that it is effective at killing a broad range of pathogens and that it is relatively inexpensive. It also leaves very little residue or film on surfaces. However, chlorine is corrosive to equipment and water pH must be monitored and adjusted often to maintain chlorine in its active form. Continual addition of chlorine without changing the water can result in the accumulation of high salt concentrations that may injure some products. Further, chlorine can react with organic matter to form small amounts of different trihalomethanes (THMs) that are thought to be carcinogenic. However, the relative risks from chlorine-generated THMs on the surface of fresh horticultural produce is extremely low.
Chlorine dioxide (Cl02)
Chlorine dioxide is a synthetically produced yellowish-green gas with an odor like chlorine but with 2.5 times the oxidizing power of chlorine. This higher potency translates into less chemical required for the same sanitizing effects compared to chlorine. Chlorine dioxide is typically used at concentrations between 1 and 5 ppm. However, it usually must be generated on-site because the concentrated gas can be explosive and decomposes rapidly when exposed to light or temperatures above 50oC (122oF). These concentrated gases also poses a greater risk to workers than sodium or calcium hypochlorite. Noxious odors from off-gassing
can be a common problem, especially at higher concentrations, which restricts its use to well-ventilated areas away from workers. Unlike chlorine, chlorine dioxide does not hydrolyze in water and is virtually unaffected by pH changes between 6 to 10 and does not react with organic matter to form THMs. However, in addition to C102, some generators produce free chlorine that may form THMs and C102 may produce other potentially hazardous byproducts (e.g. chlorate and chlorite). One additional drawback is that simple assays to monitor chlorine dioxide concentration are currently not available.
Peroxyacetic Acid (PAA)
Peroxyacetic acid is a strong oxidizer formed from hydrogen peroxide and acetic acid. The concentrated product (40% PAA) has a pungent odor and is highly toxic to humans. PAA is very soluble in water with very little off-gassing and it leaves no known toxic breakdown products or residue on the produce. Unlike chlorine and ozone, it has good stability in water containing organic matter, which can greatly increase the longevity of the sanitizer, and it is not particularly corrosive to equipment. PAA is most active in acidic environments with pH between 3.5 and 7, but activity declines rapidly at pHs above 7-8. High temperatures and metal ion contamination will also reduce its activity.
Ozone gas is one of the strongest oxidizing agents and sanitizers available. An expert panel declared ozone to be Generally Recognized As Safe (GRAS) in 1997 and ozone is currently legal for food contact applications. Although ozone is not particularly soluble in water (30 pg/ml or 30 ppm at 20 OC), concentrations as low as 0.5 to 2 ppn are effective against pathogens in clean water with no soil or organic matter. In practice, even concentrations of 10 ppm are difficult to obtain and concentrations of 5 ppm are more common.
Ozone decomposes quickly in water with a half-life of 15 to 20 minutes in clean water but less than a minute in water containing suspended soil particles and organic matter. Thus, ozonated water should be filtered to remove these particulates. The cooler temperatures of hydrocoolers may also extend ozone's half-life. The antimicrobial activity of ozone is stable between pH 6 and 8 but decomposes more rapidly at higher pHs. Ozone breaks down to oxygen and no other toxic by-products have been reported.
Because of its strong oxidizing potential, ozone is toxic to humans and must be generated on-site. Prolonged exposure to more than 4 ppm ozone can be lethal. Ozone has a pungent odor that can be detected by humans at 0.01 to 0.04 ppm. OSHA has set worker safety limits of 0.1 ppm exposure over an 8 hour period and 0.3 ppm over a 15 minute period. At concentrations in water above 1 ppm, off-gassing can result in concentrations in the air that exceed OSHA limits of 0.1 ppm. Another disadvantage of using ozone is that it is highly corrosive to equipment, including rubber and some plastics.
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