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Institute of Food and Agricultural Sciences
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________________________________________________ Institute of Food and Agricultural Sciences |
Southwest Florida Vegetable Newsletter
January -February 2002
March 18 -19, 2002
Spanish Core and Private Applicator Testing
Dallas B. Townsend Agricultural Center
LaBelle, Florida
For more information call Sheila or Gene at 863-674-4092.
March 21 - 24, 2002
34th Annual Florida Watermelon Association Convention
Hyatt Regency, Tampa City Center
Tampa, Florida
For more information contact Patty Swilley at 941-658-1442.
March 28, 2002
Train-The-Trainer class
Dallas B. Townsend Agricultural Center
LaBelle, Florida
For more information call Sheila or Gene at 863-674-4092.
April 9 - 10, 2002
Pesticide Training Class
Dallas B. Townsend Agricultural Center
LaBelle, Florida
For more information call Sheila or Gene at 863-674-4092.
June 2 - 4, 2002
Florida State Horticultural Society 115th Annual Meeting
Marco Island Mariott Resort & Golf Club
Marco Island, Florida
For more information contact Kathy Murphy at 407-673-7579 or
fshosociety@aol.com or go to
http://www.lal.ufl.edu/fshs
December 8-12, 2002
Cucurbitaceae 2002
Naples Beach and Golf Club
Naples, Florida
Contact Don Maynard at 941-751-7636 ext 239 or dnma@mail.ifas.ufl.edu
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Gene McAvoy
Vegetable Extension Agent II Hendry County Extension Office PO Box 68 LaBelle, Florida, 33975 863-674-4092 |
It’s official folks—the latest word from the Florida Fish and Wildlife Conservation Commission indicates that there are now probably more panthers in Southwest Florida than vegetable growers. There area not only are more of the big cats than growers they receive a lot more assistance than do vegetable producers.
Recently the State of Florida moved to purchase some 21,000 acres of prime agricultural land in Hendry County for panther habitat. The purchase price was over $35 million dollars. This is just the first of a number of proposed purchases to acquire land for the Panther Glades project. According to one map, the state’s wish list for additional land acquisitions for this project include almost all of Alico Ranch and adjoining parcels that would eventually encompass most of the land south of Sears Road stretching from Hwy 29 to CR 835 and south to Hwy 846.
In addition to this the state also has it’s eye on additional lands along a corridor that runs south and west of Hwy 856 in Collier County. These lands encompass much of the vegetable acreage in southwest Florida and consist of some of the most productive and last remaining open agricultural land in the southern part of the state.
While it is uncertain what the final expenditure on land acquisitions for panther habitat will be—it is quite likely that the citizens of Florida will end up spending in excess of $1 million dollars per panther.
Something seems horribly wrong with this picture. Am I missing something or do we need to reevaluate our priorities? The citizens of Florida are laboring in a stagnant economic environment where the legislature cannot find the money to adequately support the education of our children—the future of our society. Funding for critically needed research and research institutions that support agricultural producers has been slashed repeatedly to a point that threatens programmatic integrity.
While there is no doubt that the economic downturns of the past year have impacted government revenues, it seems we should concentrate our limited resources on supporting productive enterprises that will help generate the revenues needed to pull us out of the current economic rut and prepare our youth to become successful and productive citizens before we can afford to establish a giant cat-house in southwest Florida.
Agricultural has traditionally been the driving force that has helped ensure the preservation of large tracts of wildlife habitat in Florida, surely we can find way to continue preserve the symbiotic co-existence of agriculture and wildlife. If you have an interest in the long term survival of our industry, you owe it to yourself to call, write or otherwise communicate your views to your elected officials and help bring some sanity and the reorganization of priorities to this process.
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A number of soilborne fungi are considered to be limiting to the production of conventionally and organically grown vegetables for the fresh market. Members of the genera Fusarium, Pythium, Phytophthora, Sclerotium, and Rhizoctonia are of primary concern. Several biologically-based disease management products have been developed for use against these fungi. The 8 organisms commercially available in the US as controls for soil-borne diseases in vegetable crops are listed in Table 1. Several are found in more than one product, generally distinguished by the formulation. The Organic Materials Review Institute has labeled 8 of these products as allowable for use in certified organic operations.
A survey by Glades Crop Care of South Florida tomato, potato and pepper growers in 1996-1997 indicated that, while the majority of growers commonly used IPM techniques of scouting, resistant varieties and cultural controls, the "addition of mycorrhizal organisms to transplant or field soil to mitigate soil-borne diseases" was not commonly used. Frantz and Mellinger (1998) cite the lack of clearly demonstrated efficacy as the primary barrier to the use of biologically-based disease management products.
A wide variety of disease-suppressing organisms, including most of those listed in Table 1, have been tested in Florida on different crops and under different conditions. A summary of the results is listed in Table 2. Sources for the specific tests are listed in the Literature Cited section or were provided by the companies producing the biocontrol products. As suggested by the Glades Crop Care survey, results varied with crop, variety, cultural conditions and method of application. However, some studies do show the potential that biofungicides have for controlling soil-borne diseases. It is important to note that biological control organisms are not meant as stand alone disease control strategies, in that they suppress but do not control disease. Therefore, these organisms should be evaluated as components within an integrated system of cultural, chemical and biological controls.
Variations due to site, year, level of disease, cultivar, etc. are the norm and therefore tests must be repeated over time and location to produce useable results. Information on yield as well as on disease response and the inclusion of on-farm trials will be more likely to result in adoption of the technology by growers.
Vegetarian
02-02
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| Table 1. Commercially Available Biologically-based Disease Management Products for Control of Soil-borne Organisms in Vegetable Crops. | ||||
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Trichoderma viride |
Promote Plus x |
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(dried fermentation products) |
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| y EPA
Experimental Use Permit
x Allowed for organic production by the Organic Materials Review Institute z may not be available |
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Lower disease incidence |
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aphanidermatum |
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No reduction in severity of wilt |
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Equal control to Vydate |
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No reduction in disease incidence |
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Colonized roots |
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Reduced disease incidence |
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No reduction in disease incidence |
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No reduction in severity of wilt |
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Reduced disease incidence on average 30% |
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root rots |
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No effect on length and weight, reduced disease incidence in combination with Glomus intraradices |
| Trichoderma harzianum |
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Colonized roots Increased plant height and weight |
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Did not control disease |
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Reduced disease incidence Did not increase yield |
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Higher yield than untreated control |
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Colonized roots |
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Reduced disease severity and incidence (not significantly different from control) |
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No reduction in severity of wilt |
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No reduction in disease incidence |
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No reduction in disease incidence |
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Improved transplant growth, Good root colonization, Higher yields in fumigated soil (not significantly different from control) |
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Control equal to metalaxyl |
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Colonized roots |
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No plant stimulation or yield increase |
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No reduction in severity of wilt |
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No reduction in disease incidence |
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No reduction in disease incidence or severity. No increase in yield on fumigated soil. Trend for increased yield on non-fumigated soil. |
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Farm Bureau Member Memo
February 2002
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“This Web site is a tool that researchers and policy makers can use to examine research needs and priorities in food safety," said Agriculture Secretary Ann Veneman. "The goal is to measure the progress of our food safety research and continue efforts to educate the public about these important issues."
The searchable database provides information on nearly 500 food safety research projects dating from 1998 to the present. The site includes research done or funded by: USDA Agricultural Re search Service; USDA Cooperative State Research, Education, and Extension Service; the Food Safety Consortium (researchers from the University of Arkansas, Iowa State University, and Kansas State University); and the U.S. Department of Health and Human Services' Food and Drug Administration.
Also on the Web site are program and planning information, various food safety reports, food safety news and information and more than 100 links to Web-based food safety research information provided by U.S. and foreign governments and educational and professional organizations.
Vegetable Growers News
November 2001
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"One of the unique biological features of M. albus is that it produces volatile natural compounds that are extremely effective in controlling many plant pathogenic fungi and bacteria as well as microorganisms that are pathogenic to humans," explained Strobel. "I believe this is the world's first mycofumigant."
"I chose AgraQuest as my commercial partner for agriculture and industrial uses because of their core competency in microbial natural products and their proven ability at quickly commercializing microbial products," added Strobel.
"AgraQuest is targeting the same markets as the fumigant methyl bromide - largely high-value specialty crops including fruits and vegetables," said Jim Chambers, Director of Sales and Marketing, "because the chemical is currently being phased out and AgraQuest already has a presence in these markets through the sale of our Serenade® Biofungicide."
Beyond targeting the current uses of methyl bromide, AgraQuest is also targeting the control of mold and bacteria that cause sick building syndrome. This problem occurs when certain types of microorganisms infect buildings and cause health problems including headaches, respiratory troubles, nosebleeds, and memory loss.
AgraQuest is a biotechnology company that focuses on discovering, developing, manufacturing and marketing effective, safe and environmentally friendly natural pest management products for the agricultural and institutional and home markets. AgraQuest is developing and commercializing a pipeline of natural pest management products, including its first product, Serenade®, and believes that its proprietary technology platform will be the foundation for the discovery and development of natural products for the pest management industry.
Certain matters contained in this press release concerning AgraQuest, Inc. are forward-looking statements which are subject to known and unknown risks and uncertainties which may cause the Company's actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by these forward-looking statements. Such risks and uncertainties include, among others, the receipt of EPA and other regulatory approval of the Company's products, the success of the Company's products in field trials, and the timely development, manufacture and marketing and acceptance of the Company's products in the marketplace.
AgraQuest, Inc.
(January 7, 2001)
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AgraQuest, Inc. announced today a new research initiative with the University of California, San Diego, funded in part by a BioStar (Biotechnology Strategic Targets for Alliances in Research) award. The joint funding will support research aimed at investigating deep marine sediment microbes for use as biological pest management solutions for controlling fungal disease, insects and nematodes. The research will be carried out in collaboration with the laboratory of Dr. William Fenical (Scripps Institution of Oceanography, UCSD), a professor internationally renowned for his important discoveries of new pharmaceuticals from naturally occurring marine microorganisms. Through novel sampling, isolation and culture techniques, Dr. Fenical’s laboratory has discovered a new group of marine microorganisms that have never been tested as crop protection agents. This gives AgraQuest, Inc. a unique source of biologically active agents for development of new products for pest management.
“AgraQuest is pleased to have exclusive access to this newly discovered source of microbes for use in crop protection. While our first product, Serenade®, was developed from a soil microorganism, there is much potential in accessing novel microbial diversity for future product development,” said Pam Marrone, CEO of AgraQuest, Inc. “In addition to our own discovery efforts, collaborating with the leading natural product researchers is our strategy to become the leader in the area of natural product solutions for pest management.”
“We are pleased to have a good outlet in the pest management arena for this exciting new group of microorganisms,” said Dr. Fenical.
Founded in 1996, the Industry University Cooperative Research Program (IUCRP) administers BioStar grants to fund research undertaken in partnership with the private sector to yield benefits for the California economy. This has helped California businesses to successfully transform new knowledge from University labs into new technologies and products providing a foundation for job growth and economic expansion.
AgraQuest
February 8, 2002
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The federal Office of Research Integrity just ruled that Steven F. Arnold, a former researcher at the Tulane University Center for Bioenvironmental Research, “committed scientific misconduct by intentionally falsifying the research results published in the journal Science and by providing falsified and fabricated materials to investigating officials.” Arnold lied and then covered up.
The ORI also found that, “there is no original data or other corroborating evidence to support the research results and conclusions reported in the Science paper as a whole.”
The disturbing tale began in 1996 with the publication of the book Our Stolen Future: Are We Threatening Our Fertility, Intelligence and Survival? — A Scientific Detective Story. The book was a compendium of loosely told anecdotes that attempted to implicate chemicals in the environment and our food — such as PCBs, pesticides and plastics — as the cause of diseases ranging from cancer to infertility to attention deficit disorder.
The authors of Our Stolen Future speculated that these chemicals — so-called “environmental estrogens” or “endocrine disrupters” — disrupted normal hormonal processes, even at low exposure levels generally accepted as safe.
Although Our Stolen Future initially received a great deal of media attention, it soon died out amid much criticism from many respected scientists. But just when the fury faded, Arnold and his Tulane gang published their study in June 1996, claiming that combinations of pesticides and PCBs were up to 1,000 times more potent as endocrine disrupters than the individual chemicals alone.
“The new study is the strongest evidence to date that combinations of estrogenic chemicals may be potent enough to significantly increase the risk of breast cancer, prostate cancer, birth defects and other major health concerns,” said then-EPA chief Carol Browner.
“I was astounded by the findings,” said then-EPA pesticide chief Lynn Goldman. “I just can't remember a time where I've seen data so persuasive … The results are very clean looking.”
The study received a great deal of publicity that stampeded Congress into passing a bill in July 1996, signed into law by President Clinton, requiring the EPA to develop a program for screening thousands of chemicals for their ability to act as endocrine disrupters.
The EPA's Endocrine Disrupter Screening Program now underway only costs about $10 million per year. But the cost to industry and consumers will likely stretch into the billions of dollars. Testing of a single chemical can easily reach into the millions of dollars.
The Arnold study began to unravel a mere six months after publication. Scientists from around the world began to report that they could not reproduce Arnold's results — such replication of results being a requirement for findings to be considered as “scientific.”
By August 1997, Arnold was forced to retract his study from publication. His retraction stated, “We … have not been able to reproduce the results we reported.” He later added, “I can't really explain the original findings.”
Now we know why — he cheated. The penalty imposed on Arnold was a five-year ban from federal grants.
Although a lifetime ban and perhaps even criminal prosecution would have been more appropriate — after all, he was found guilty of “intentionally falsifying” taxpayer-funded research — the light penalty is not the most disturbing part of this story.
Arnold's study has been thoroughly trashed, but the federal law remains and the mandated EPA testing program is in full bloom.
In August 1999, an expert committee of the National Academy of Sciences' National Research Council — a panel that included scientist representatives from the environmental activist community — reported there was no evidence that chemicals in the environment were disrupting hormonal processes in humans and wildlife.
That scientific report was inexplicably insufficient to kill the endocrine disrupter scare. But now, if proven fraud isn't enough, what is?
Cato Institute, 2001
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SUNSHINE STATE |
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Farm Bureau Member Memo
February 2002
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5E-9 - Pesticide Certification and Licensing Effective March 1, 2002 |
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Aerial CEUs. The number of CEUs required to renew the aerial category is being increased from 8 to 16 CEUs. Like other applicators, aerial applicators will be required to have a minimum of 2 core CEUs for each primary category, including the aerial category. So of the 16 CEUs required to renew the aerial category, at least 2 must be core CEUs, and at least half must be aerial CEUs. The remainder of the required CEUs for the aerial category can be either core or aerial CEUs.
Core CEUs. Effective January 1, 2005, all applicators licensed under Chapter 487, F.S., who renew their licenses using Continuing Education Units (CEUs) will be required to have 4 core CEUs in addition to the number of category CEUs now required. At that time, all category CEUs must be approved for the specific category. There will no longer be a requirement for having 2 core CEUs per primary category, and core CEUs will no longer apply to the required number of category CEUs. Applicators will have the option of retaking the core and/or category exams if they do not have enough CEUs for renewal.
Example: Effective January 1, 2005, private applicators will be required to have 4 core CEUs plus 8 CEUs approved for the private applicator agriculture pest control category. A private applicator who has 8 private applicator CEUs and only 2 core CEUs may choose to take the core exam instead of earning 2 additional core CEUs, if desired.
Educational Modules. The CEU program approval rule is being revised so Department-approved educational modules can be approved for CEU credit in addition to professional training meetings and seminars.
Pesticide Dealer Records. The record keeping requirements for pesticide dealers are being revised to require records to be kept for product exchanges as well as sale of restricted use pesticides. Also, the information to be kept in the records was modified to require both the name of the licensed applicator and the name of the authorized purchasing agent making the purchase, if applicable. This change will be effective about April 1, 2002.
Direct Supervision. Licensed applicators who supervise unlicensed individuals who mix, load, or apply restricted use pesticides will now be required to be immediately available by voice communication to the unlicensed individuals to provide direction and instruction during all times restricted use pesticides are being used.
Forms. Updated versions of the following Department forms were adopted:
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Sandea: A state label (24c) is in place at the present time for the use of Sandea (halosulfuron) on cucumbers. Sandea is excellent on the control of emerged nutsedges. It will also control small emerged smooth and spiney amaranth. Recently, we have seen that it will not control emerged livid amaranth in southwest Florida.
A section 18 label is being requested for the
use of Sandea in tomato. FFVA is requesting this use. Tomatoes are very
tolerant, both pretransplant and POST over-the-top. A tolerance for halosulfuron
is pending this quarter at EPA. Do not apply Sandea to over-the-top of
pepper. Pepper is very sensitive to POST applications.
EPA has just approved a tolerance for a
halosulfuron on muskmelon and watermelon. Gowan will be discussing their
intentions for labels on these two crops at the WSSA meetings on Feb 11.
I should know more at that time.
Aim: Aim (carfentrazone) is labeled for burn down of broadleaf weeds and morning glories in sweet corn in Florida. Residue studies have been carried out through the IR-4 program in tomato and pepper row middles. Aim will control paraquat resistant nightshade among other weeds in the row middles. FMC and FFVA are seeking section 18 label for this use in tomato, pepper and eggplant row middles. The application will be as a directed-shielded application, the same as paraquat is at the present.
Matrix: Matrix (rimsulfuron) is labeled in Florida on potatoes. For a short period of time, rimsulfuron was labeled in Florida under the trade name Shadeout. DuPont pulled all Shadeout labels on fresh market tomatoes, and it is only labeled on processing tomatoes at the present time.
TPR, Inc. has come to an agreement with DuPont and is now in the process of submitting a 24c third-party-registration for Matrix on tomatoes in Florida. Matrix is safe, both PRE and POST on tomatoes, and will control a large number of broadleaf weeds. Again, peppers are not tolerant to POST applications.
Curbit: UAP has informed me that they are going to quit selling Curbit (ethalfluralin). They have, however, received a registration for Strategy, a premix combination of ethalfluralin + clomozone. The label of Strategy will be the same as the Curbit label. The product should be safer, however, than Curbit. In my trials, the product has been safer and has a larger control range than Curbit. Again, it should not be used for transplanted melons nor used under mulch.
Stall
Vegetarian 02-02
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How and where does one actually find postharvest
information on the Internet? One way is by using a web search engine such
as Google (http://www.google.com/
), Alta Vista (www.altavista.com), HotBot
(www.hotbot.com), or Yahoo (www.yahoo.com).
Web ‘crawlers’ such as "Dogpile" (http://www.dogpile.com/
) can often find more information by pooling the resources of several different
search engines. One drawback of using search engines, though, is that they
often return sites not particularly related to the topic of interest but
simply have the search word(s) present somewhere in the page. Once a useful
web site has been found, it often includes links to similar web sites so
that further information on that topic can be found by following the links.
By saving or "bookmarking" particularly useful sites with links to other
related sites, one can easily return to the source of information.
The University of Florida’s main postharvest
site is the UF Postharvest Programs and Information website
(http://postharvest.ifas.ufl.edu).
At the site, one can search for information using key words or by using
the topical index to browse information organized into the following subject
areas:
(Ritenour, Sargent, and Brecht
Vegetarian 02-01)
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Farm Bureau Member Memo
February 2002
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BMPs and TMDLs are much at the forefront of today’s
vegetable growers’ concerns. BMPs are best management practices;
TMDL stands for total maximum daily loads. The TMDL have their legislative
origin, the Clean Water Act of 1972, and represent the maximum amount of
a compound that a water body may absorb each day and still maintain water
quality parameters consistent with its designated use. Each water body
will have a TMDL for each compound. BMPs are specific cultural practices
that will help reduce load, and thereby the environmental impact of vegetable
production.
In Florida, the two main elements targeted by
the TMDLs and BMPs and of interest to vegetable growers are nitrate (N-NO3)
and phosphorus. Because it is negatively charged, nitrate is not held by
the soil colloids and clay minerals (which are negatively charged themselves,
and therefore, only tie positively charged ions or cations) and thus moves
freely as a solute. When heavy rainfall or excessive irrigation occur,
nitrates move vertically in the soil profile and below the root zone.
Ultimately, it will reach ground water and will contribute to eutrophication.
Phosphate movement, in contrast, is believed to mainly occur during sediment
movement at the soil surface. When surface erosion occurs, phosphorus is
carried into ditches and streams where it also contributes to eutrophication.
In their intent, BMPs are cultural practices
that reduce the environmental impact, while maintaining yields. Hence,
the purpose of the BMPs is not to reduce fertilization to an unacceptable
level. At first, TMDLs and BMPs were perceived by agriculture in general
and the vegetable industry in particular as another round of government
regulation. However, with federal and state regulations in place and environmental
groups pressing for their enforcement, the TMDL and BMP process has been
irreversibly initiated. In recent months, industry members attitudes have
changed from hoping the process will stop and go away, to seeking ways
to be best prepared for the BMPs. Reasons for this change have included
increased incentive programs, increased information, and pilot programs.
So, what is in for vegetable growers to embrace
the TMDL concept and implement the BMPs in their operations? The largest
incentive, by far, is the ‘presumption of compliance’. Growers having a
BMP plan (or whatever the final name will be) and following it will be
granted presumption of compliance with the TMDL. This is no small incentive.
The second group of incentives are the financial help that will be available
to implement the BMPs. Hence, in theory, the implementation of the BMPs
should be at no financial cost for the farmer. That’s the way it looks
now.
Objectives of this article.
Whatever their final form will be, it is clear that BMPs will require not only a higher level of nutrient management, but also adequate irrigation management. The objective of this article is to present (1) the principles of irrigation scheduling, and (2) how they can be applied in regard to the BMPs.
Basics of Irrigation Scheduling
Scheduling irrigation is to know when to start
irrigation and how much to apply, in a way that satisfies crop water needs,
conserve water, and does not leach mobile nutrients. Because of the low
soil water holding capacity of Florida’s coarse-textured soils, irrigation
frequency for spring crops is commonly once a day, and sometimes two to
three times daily. As an aid to schedule irrigation, the water balance
method is a simple process that accounts for all the sources and losses
of water from the root zone of actively growing vegetable crops. Water
inputs into the root zone are rainfall, irrigation, and upwards vertical
capillary movement. Water losses out of the root zone are surface runoff,
percolation, and evapotranspiration. For the purpose of scheduling,
the water balance may be formulated as: water addition in the root zone
should be exactly off set (or balanced) by the water losses, so that the
fluctuations in soil moisture the plants are exposed to are small. The
only water fractions that the vegetable grower has control over are irrigation,
and to a lesser extend, surface run off and deep percolation.
Scheduling irrigation requires (a) a target water
amount to be applied, (b) guidelines on how and when to split irrigation,
if necessary, (c) a method to account for rainfall, and (d) a practical
method to monitor soils water tension (SWT). The IFAS irrigation recommendation
for vegetables are based on the Penman-Montheith method for estimating
reference evapotranspiration (ETo), and a crop coefficient (Kc) used to
adjust ETo to estimated crop evapotranspiration (ETc) using the relation:
ETc = ETo x Kc. It is also recommended to maintain SWT between field capacity
(6 to 8 cb) and 15 cb.
Principle 1. Irrigation amount must reflect
crop water use....no more, no less.
Irrigation amounts may be estimated using historical
weather data (H-ETo), climatic measurement in real-time (RT-ETo), class
A pan evaporation data (Ep), atmometers (A-ETo), and empirical amounts.
While simple, this method has several limitations. First, it does not account
for year-to-year variability. Also, historical weather data are available
from a limited number of locations. Finally, most Kc values currently available
(except for strawberry and tomato) were developed for bare-ground production.
As an alternative to historical weather data, RT-ETo may be collected on-farm
with a small weather station. Relatively inexpensive weather stations ($1,500
to $2,000) are now available to collect radiation, wind speed, direction
and mileage, and rainfall. Data can be stored automatically in a data logger
and later downloaded for other usages using a lap-top computer. These automated
stations provide a real-time estimate of ETo in time increments as short
as a few minutes. Daily estimates (every 24 hours) are usually adequate
to schedule irrigation for vegetable crops.
Water evaporation from a class A pan (defined
as a galvanized, round, 30-cm deep, 1.20 cm in diameter pan placed in the
center of a grassy area) can be used to estimate crop water use (ETc) by
adjusting Ep with a coefficient called crop factor (CF) using the equation
ETc = Ep x CF. Class A pans cost approximately $500 each. However, research
has shown that other less expensive containers (such as No.2 wash tub or
sections of 55-gallons drums painted with reflective paint) may be used
as practical tools to estimate Ep when class A pans are not available.
All pans may be covered by chicken wire to ensure all water losses in the
pan are due to weather demand, and not from animals such as birds and small
mammals, drinking from the pan.
Current research at the North Florida Research
and Education Center - Suwannee Valley is also evaluating simple atmometers
as a practical tool to estimate ETo. Atmometers are made of a water reservoir
and a small, green, sponge-like circular surface. The sponge-like material
is connected to the water reservoir. As water demand for weather increases,
water is draw from the reservoir through the sponge-like material. A graduated
column allows a simple reading of water volumes in the reservoir. The top
of the sponge-like material is flanked by two small 4-in long straight
wires that help prevent birds from landing and drinking some water. Because
these two pieces of metal look like antennae, this type of atmometer
is sometimes referred to as ‘the water bug’.
Whatever the device it is collected with (weather
station, class A pan, home-made evaporative pans or atmometer), the main
advantage of RT-ETo is that it is available in real time. RT-ETo is a true
representation of the climatic conditions and water demand the crop has
been exposed to. It is therefore a very practical tool to schedule irrigation.
Research is currently underway at the North Florida Research and Education
Center - Live Oak to develop CF values for real-time irrigation scheduling
of watermelon and bell pepper. In contrast, the disadvantages of RT-ETo
are limited to reading the equipment, maintaining it, and using the appropriate
coefficient (Kc or CF) to estimate Etc. RT-ETo is likely to be a part of
the irrigation BMP, in a form that is yet to be determined.
Another possible alternative for use when no
weather data are available is to use an empirical value for irrigation
amounts. Because of its simplicity, this is the method most commonly
used by small-scale vegetable growers. As a general guideline, vegetables
receive daily irrigations of 1 hour when they are small (first third of
the vegetative period) to 3 hours when they are large (during fruit development
and close to harvest). When drip tapes with a flow rate of 0.25 gal/minute/emitter
and 12-in emitter spacing (or 15 gal/hr/100ft), this schedule applies 15
gallons/100ft/day for small plants, and 45 gallons/100ft/day for large
plants. Intermediate values are used during crop growth. Empirical values
have the advantage of being simple. However, they often result in excessive
irrigation early in the season, and insufficient ones later in the season.
This method alone (without monitoring of soil water tension) is likely
not be acceptable for the BMPs.
Principle 2. Irrigation amount should
not exceed soil water holding capacity. Otherwise, water is wasted
and mobile nutrients are leached.
How far water moves down the soil profile is
a rather abstract concept because it is not visible. However, it is possible
to visualize soil water movements by using colored dyes. The series of
figures show the wetting pattern created by a single or double drip tapes
with 24 gal/hour/100ft flow rate and a 12-in emitter spacing. Figure 1
shows longitudinal profiles, and Figure 2 and Figure 3 show transverse
profiles. A water soluble dye was injected with a dosatron using 1:69 dilution
for the first 10 minutes, and 1:500 for the remaining 50 minutes.
Theoretical highest irrigation amounts can be
simply calculated based on the soil physical properties. For a soil where
the wetting width is 12 inches (6 inches each side of the drip tape), assuming
a 0.75in/foot soil water holding capacity and allowing a 50% soil water
depletion, theoretical largest water amounts that can be stored in the
soil are 24 gal/100ft within the top 12 inches, 36 gal/100ft within the
top 18 inches, and 48 gal/100 ft within the top 24 inches. These numbers
can be used as guidelines. Actual amount that can be applied in one irrigation
also depends on the rate of crop evapotranspiration, number of drip tapes,
and soil type.
Principle 3. Rainfall little contributes to
replenish soil moisture ... because of the plastic mulch.
Several IFAS fertilizer recommendations for bare
ground production allow for additional N and K fertilizer after leaching
rains. Leaching rains are defined as three inches of rain in three
days, or four inches in seven days. Since the plastic mulch protects the
bed from rainfall, there is no need in theory to apply additional fertilizer
after a leaching rain. When the field gets partially flooded, however,
some mobile nutrients may be leached out of the root zone or carried out
of the field through surface run off. The need for additional fertilizer
may be assessed after field drainage by monitoring sap tests levels of
nitrate and potassium.
Another consequence of using the plastic mulch
is that an irrigation may be still needed after a small rain. Soil water
tension measurement (as explained bellow) can be used to assess the need
for additional irrigation.
Principle 4. Monitor soil moisture level daily ... and discover how much water stress the crop is exposed to.
Soil moisture is typically reported in terms of
soil water tension (SWT) or volumetric water content (VWC). SWT represents
the suction force that is necessary to free soil water from the soil attraction.
The higher the absolute value of SWT, the greater is the force needed.
In some publications, SWT values are reported as negative values. The ‘-’
sign is there to reflect the fact that the attraction is generated by the
soil particles and therefore the plant has to spend energy to absorbe water.
SWT may be expressed in atmospheres (atm), bar (b), or Pascals (Pa; the
international unit). The conversion between units is 1 atm = 1.013 b =
1013 mb = 105 Pa. The recommended range for vegetable production is to
maintain SWT between 6 to 8 cb (field capacity) and 15 cb. Vegetables may
tolerate more extreme SWT (up to 25 cb) without yield reduction. However,
sandy soils with SWT above 15 cb may be difficult to re-wet.
VWC represents the volume of water present in
a volume of soil. The relationship between SWT and VWC is not linear, but
is instead hyperbolic-like. When VWC is high (close to maximum soil water
holding capacity), a relatively large change is VWC will result in a small
change in SWT. However, when VWC is much less than maximum soil water holding
capacity, a small change. Hence, the relationship between SWT and VWC (called
water release curve) is typical for each soil type and is necessary to
convert the recommendation in terms of tension into a recommendation expressed
in terms of volumes.
Instruments used to routinely measure soil moisture
either determine SWT (granular matrix sensor or GMS, and tensiometers)
or VWC (time domain reflectometry probes or TDR, and electrical conductivity
probes or EC robes). Tensiometers are based on the principle that
changes in moisture in a porous cup in equilibrium with the soil can be
expressed in changes in air pressure inside the cup. The advantages of
tensiometers are their relatively low cost ($60 to $90 each, depending
on the length of the access tube, and their accuracy. Their disadvantages
include (1) they need to be serviced regularly, (2) they are easily breakable,
and (3) the contact between the porous cup and the soil may be easily
lost in sandy soils, thereby displaying an erroneous SWT reading. For the
growers who have learned to use them, tensiometers are a useful tool. For
most, they are a nightmare. Another tool available to measure SWT are the
GMS. Their principle of operation is based on the fact that in saturated
saline condition, electrical conductivity is a function of moisture. GMS
are made of a capsule that contains a sand-like material (hence the name
‘granular matrix’) that embeds two concentric electrodes. The moisture
in the granular matric is in equilibrium with that of the soil. GMS are
relatively easy to install, cost $35 for a sensor and $350 for a reader,
and do not require maintenance. GMS have been successfully tried
and adopted by several vegetables growers in North Florida during an on-farm
demonstration program. Tensiometers and GMS are usually installed in stations
of 2 units, one reading SWT at a 6-in depth, and the other at a 12-in depth.
Simultaneous readings at both depths allow proper management of water in
the 0-12 in zone, which represents the area of the soil where most of the
roots of most vegetable crops are located. Both types of sensors are buried
for the entire season, preferably between two representative plants, and
require a few hours to be in equilibrium with the soil. Hence, they are
not easily movable throughout the field.
A relatively new series of instruments that measure
VWC directly or indirectly is now available. The principle of TDR is that
the soil dielectric constant depends on soil moisture. A basic TDR unit
is comprised of rods, a detector and a display unit, and costs approximately
$700. The detector emits a waive that travels along the rod and records
the time needed for the waive to travel. Hence, a TDR probe reveals a VWC
value that is integrated along the length of the probe. Common probe length
are 4, 8 and 12 inches. Because of the nature of the TDR measurement, as
soon as the probe in placed into the soil, it is ready to operate. Hence,
TDR units are portable, and may be placed anywhere, instantaneously. The
advantages of TDR are that the measurement is fast and non destructible,
units may be hard-wired to a data logger.
Principle 5. Keep irrigation records daily.
Vegetable growers are required to keep pesticide
records. Fertilization records are usually kept in relation to soil testing
and implementing the recommendations. However, often times vegetable growers
do not document their irrigation practices. For example, a useful daily
log should contain soil moisture measurements (SWT or VWC) at selected
depths, rainfall and an estimate of weather demand for water (H-ETo, RT-ETo,
A-ETo, class A pan), and irrigation amount (gallons/field or duration of
irrigation). Most growers who are already keeping irrigation records find
them to be a useful management tool.
Conclusions
The environmental impact of vegetable production
is not due only to nutrient management. While elements such as nitrogen
and phosphorus are regarded as the ‘pollutants’, their fate and movement
below the root zone is conditioned by water movements. Hence, nutrient
management cannot be accomplished successfully without adequate irrigation
management. While the BMP and TMDL process is still in its beginning,
the goal is to reduce environmental impact, and not to restrict production.
Vegetables growers having a BMP plan and documenting that they follow it
will be granted presumption of compliance with the TMDL.
It is increasingly important for vegetable growers
to adequately manage irrigation. Currently, the BMPs for vegetables are
being defined, and the process is not completed. However, it is likely
that in a form or another, these principles (using real-time or empirical
water use estimate to determine target volume; adopting and following
specific guidelines on how/when to split irrigation; adjust irrigation
practices for plasticulture; routinely monitoring soil moisture status,
and keeping daily records of irrigation practices) will be included part
of the BMPs.
Eric Simonne, Mike Dukes, Bob Hochmuth,
David Studstill and Wayne Davis
Vegetarian 02-02
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The man replied, "I'm from the phone company. I came to hook up your phone."
Alcoholic Side-Effects
The FDA is considering additional warnings on
beer and alcohol bottles, such as:
