Horticultural Sciences Department

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Issue No. 611

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
April 2016

Water Management and Vegetables, What’s New?

Kati W Migliaccio (Professor), Michael D Dukes (Professor and Director of CLCE), and Clyde Fraisse (Associate Professor)

Faculty in the Agricultural and Biological Engineering Department have been involved with improving the viability of vegetable production through better water management. This article highlights some of the on-going work in vegetables and how the research outputs are meant to provide growers with better water management tools. Specifically, we cover the use of new technology/methodology in irrigation application, scheduling tools, and climate based resources.

An innovative technology that is being tested at Live Oak, Florida, is variable rate irrigation (VRI) on a linear move system (Figure 1). This three-year project proposes to determine the effect that precision irrigation management and electrical conductivity tracking have on management of water and the related crop productivity. The current experiment is being conducted with corn and peanut by Dr. Michael Dukes research group; however, this technology could be used with any crop on a linear or center pivot system. The variable rate characteristic allows the operator to modify the amount of water irrigated throughout the field so that water applications more closely match water needs. Many fields are not uniform in soil type, soil depth, drainage characteristics, and other factors that influence water dynamics in the soil-plant system. The use of VRI systems allow irrigators to apply variable rates of water throughout the field accounting for these differences. Previous research with VRI irrigation systems has shown up to 26% water savings (Evans and King, 2012).


Figure 1. VRI linear move system irrigating corn at Live Oak, Florida.

Another method of improving water management in vegetable production is through informed irrigation scheduling. Irrigation scheduling can be improved by incorporating weather or soil-water information into developing schedules. A variety of tools are availablefor incorporating weather data, including the Florida Automatic Weather Network (FAWN), FAWN’s My Florida Farmer Weather system, weather-based or ET controller (Kisekka et al., 2013), or smart irrigation apps (smartirrigationapps.org; http://www.abe.ufl.edu/faculty/kwm/apps.html; Migliaccio et al., 2016). Weather-based methods are typically used to determine irrigation by calculating the difference between water losses (i.e., evapotranspiration, ET) and water gains from rainfall or I = ET - R. There are some limitations to weather-based approaches; in Florida, the limitation is typically accurate rainfall data and crop coefficients. Crop coefficients for some Florida crops are summarized in the UF IFAS Vegetable Production Guide and Dukes et al. (2012).

An alternative to weather-based scheduling is to schedule irrigation based on soil-water content or soil water tension (Figure 2). Numerous resources are available on this topic from UF IFAS EDIS (e.g., Munoz-Carpena and Dukes, 2008; Migliaccio et al., 2012; Zotarelli et al., 2013; Zotarelli et al., 2016). Either of these scheduling approaches or a combination of them will improve water management. Another aspect that can be integrated into scheduling is forecast data. In this approach, irrigators not only use current conditions in making decision but also future predictions of rainfall and ET. The use of current weather or soil water content data and future predictions for irrigation scheduling provides a new dimension to irrigation scheduling.


Figure 2. Tensiometer installed in vegetable planting (with plastic mulch) in Homestead, Florida.

Risk assessment tools have also been developed through Dr. Clyde Fraisse’s AgroClimate program (agroclimate.org). AgroClimate offers a suite of tools that uses weather and climate data to provide information for growers that reduces the risk associated with crop production. In the Southeast there is plenty of rain --- annual rainfall averages around 50 inches --- and that should ensure good crop yields. However, other factors can reduce the usefulness of available rainfall. For example, in certain areas, such as the Florida panhandle, yields can vary substantially because soils have a low water-holding capacity, and there is always a potential for poor rainfall distribution, dry spells or low rainfall amounts during critical phases of crop growth. Temperature is also an important risk factor in crop production and of great importance to crop growth and development. Air and soil temperatures affect the germination of seeds, the rate of plant growth and development, the functional activity of plant roots, and also the severity of certain plant diseases. The Planning Date Planner tool on AgroClimate uses crop model simulations to provide users with information on yield probability for a variety of crops, including corn, potato, and tomato. The user can select different planting dates as well as a particular el Niño Southern Oscillation (ENSO) phase. Based on user selects, an output is generated and displayed (Figure 3). This is only one of the many resources available through AgroClimate to better manage risk associated with weather and climate (Fraisse et al., 2006).


Figure 3. Agroclimate-generated output showing that March 15 is the planting date with higher probability of above average yields for corn in Santa Rosa County, Florida, during El Nino years.

Linking improved irrigation methods with scheduling tools and risk assessment provide innovative practices for increasing water efficiency in vegetable production systems. These practices also help optimize profits and increase overall viability of the system. These different approaches show how science can be used to develop a variety of real-world tools.


Dukes, M.D., L.Zotarelli, G.D. Liu, and E.H Simonne. 2012. Principles and practices of irrigation management for vegetables. AE260, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date June 1995. Revised January 2012. Reviewed March 2015. Visit the EDIS website at http://edis.ifas.ufl.edu

Evans, R.G. and B.A. King. 2012. Site-specific sprinkler irrigation in a water-limited future. Transactions of ASABE 55(2):493-504.

Fraisse, C.W., Breuer, N.E., Zierden, D., Bellow, J.G., Paz, J.O., Cabrera, V.E., Garcia y Garcia, A., Ingram, K.T., Hatch, U., Hoogenboom, G., Jones, J.W., O’Brien, J.J. 2006. AgClimate: A climate forecast information system for agricultural risk management in the southeastern USA. Computers & Electronics in Agriculture 53(1):13-27.

Kisekka, I., K.W. Migliaccio, M.D. Dukes, B. Schaffer and J.H. Crane. 2010 (Updated 2013). Evapotranspiration-based Irrigation Scheduling for Agriculture. AE457. Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, IFAS, UF. URL: http://edis.ifas.ufl.edu/ae457, 6 pgs.

Migliaccio, K.W., K.T. Morgan, G. Vellidis, L. Zotarelli, C. Fraisse, B.A. Zurweller, J.H. Andreis, J.H. Crane, and D. Rowland. 2016. Smartphone Apps for Irrigation Scheduling. Transactions of the ASABE. 59(1): 291-301. (doi: 10.13031/trans.59.11158) @2016

Migliaccio, K.W., T. Olczyk, Y.C. Li, R. Muñoz-Carpena and T. Dispenza. 2012. Using tensiometers for vegetable irrigation scheduling in Miami-Dade County. ABE326. Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. http://edis.ifas.ufl.edu/tr015, 6 pgs.

Munoz-Carpena, R. and M.D. Dukes. 2008. Automatic irrigation based on soil moisture for vegetable crops. This document is ABE 356, one of a series from the Department of Agricultural and Biological Engineering, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.First published:June 2005.Reviewed: June 2008. Please visit the EDIS Web site at http://edis.ifas.ufl.edu

Zotarelli, L., M.D. Dukes, and K.T. Morgan. 2016. Interpretation of soil moisture content to determine soil field capacity and avoid over-irrigation sandy soils using soil moisture sensors. This document is AE460, one of a series of the Agricultural and Biological Engineering Department, UF/IFAS Extension. Original publication date February 2010. Reviewed February 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

Zotarelli, L., M.D. Dukes, and M. Paranhos. 2013. Minimum number of soil moisture sensors for monitoring and irrigation purposes. This document is HS1222, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date July 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.

Article 20 – Farm Labor Contractor Registration and Best Practices

Last year we wrote an overview about Farm Labor Contractor “Certificates of Registration,” commonly known as “licenses.”   In this article, we offer more of the details plus a brief explanation of a “Best Practices” designation that is in progress at the state level.   (See the end of this article).  

According to the Migrant and Seasonal Agricultural Worker Protection Act (MSPA), anyone who recruits, solicits, hires, employs, furnishes or transports any migrant or seasonal agricultural worker should be registered as a Farm Labor Contractor with the Department of Labor (DOL) and Florida Department of Business and Professional Regulations (DBPR).   Any one of those criteria means you need the FLC license.  For example, if an FLC recruits workers in Florida to work in another state, they have to be registered because they recruit. 

FEDERAL - Applications for FLC registrations have to be sent to the Department of Labor, Wage & Hour Division in Atlanta.  This process takes about six weeks. There is no fee for the DOL application, nor is there a test for that registration.  

STATE - In addition to the Federal application, an “addendum” to this application has to be submitted to the DBPR in Tallahassee for a Florida registration.  To make this application, a copy of what was sent to the DOL in Atlanta, plus the Florida state addendum form, has to be mailed to Tallahassee.  Cost for the state registration is $160 for an initial license ($125 for the license and $35 for the test).  Renewals are $125, no testing required unless:  a) you have been fined for a major violation, b) your license is revoked or suspended or the DBPR refuses to approve or renew your license (known as a “final order”) or c) the test changes due to changes in laws.  

An alternative designation to FLC is FLCE, meaning Farm Labor Contractor Employee.   An FLCE may only work for one primary Contractor and that Contractor must be identified in a separate part (Part III) of the Federal application.  This includes the primary Contractor’s name and registration number, plus indicate the approximate date the farm labor activity will begin, and the FLCE must sign this certification:  “I certify that I am an employee of the farm labor contractor identified above and will perform farm labor contracting activities only for that farm labor contractor and for no other farm labor contractor.”  The advantage of being an FLCE is that the responsibility for violations incurred by the FLCE falls on the primary contractor, not the FLCE.  The advantage to the primary Contractor of having FLCE employees is that they have to re-submit their applications if they leave employment with that contractor and go elsewhere.  

Registration is a complex process, made more complicated by the fact that the Department of Labor in Atlanta is often “behind” in their processing, and FLCs are not allowed to work until their registrations are current.   That is why it is important to send applications and amendments via a trackable mail service so you can prove when the application was received.  Two copies should be made; one for the state license and one for the FLC to keep in case any of the information they submitted was mistyped, resulting in a fineable offense of having incorrect information on a registration.

Applications have to include supporting documents.  This is where it gets tricky and is the reason many primary contractors manage the paperwork for their Crew Leaders and Drivers in-house with the Contractor’s administrative staff.   Every time one of the supporting documents expires and is renewed, an Amended application has to be filed along with a copy of the renewed document indicating the new expiration date. 

Specific authorizations on the FLC registration are needed for transportation, driving, and housing.  Note: Housing is not included on the MSPA list of activities requiring an FLC license.  If an individual only manages housing, they do not need an FLC license.  However, if someone is an FLC for one of the other reasons, and housing included as part of their job, then they must have Housing Authorization.   

In the true sense of the term, Farm Labor Contractors are businesses that contract with growers to supply labor; similar to building, roofing, or other kinds of contractors.  In farming, Contractors generally own multiple buses and/or vans as well as field trucks in vegetables or goats in citrus.  They employ multiple Crew Leaders and Bus Drivers who manage sometimes hundreds of workers.  However, all of those Crew Leaders and Drivers and other managerial employees of contractors are required to have the same FLC registration as the primary contractor.  

A statewide database is available to anyone who wants to check the registration status and obtain other information about any type of contractor or regulated business.  Go to www.myfloridalicense.com .  Select “Verify a License” and then search by Name, License Number, City or County, and License type. Then select License Category – Farm Labor.  So, for example, if you want to find a specific FLC, select name and enter their name.  If you want to see all the FLCs in Collier County, FL, select that as a county and all the registered FLCs in Collier County will show up on the list.

BEST PRACTICES - Scroll down to Additional Search Criteria to search by various authorizations of driving, transport (owner of vehicles), and housing.  At the top of this list is a field called BEST PRACTICES. This field was included in the Florida Statutes in 2002 but has never been used.

Last fall, the DBPR issued a “Notice of Development of Rulemaking” to get input as to how to define the Best Practices field. The first draft included the DBPR’s criteria and the second, published last month, incorporated some changes. They are seeking input, so if you are interested, please go to:  http://www.myfloridalicense.com/dbpr/reg/farmLabor.html. Then, in the middle of the page, click on 61L – 0.010 FAC ----   BEST PRACTICES RULE WORKSHOP AGENDA.  

There is no concrete deadline at this time for submitting comments.  However, all interested parties are advised to submit any comments as soon as possible so that they can be considered prior to the rule moving to the next step in the process.  Please contact Chevonne Christian at Chevonne.christian@myfloridalicense.com if you have questions about the rulemaking process.  

Carlene Thissen works for the University of Florida at the Southwest Research and Education Center, Immokalee, FL, 239-658-3400, carlene@ufl.edu.


The Farm Labor Supervisor (FLS) Training Program is a University of Florida/IFAS Extension program. Begun in 2010, the program is coordinated by Fritz Roka and Carlene Thissen at the Southwest Florida Research & Education Center.  In the past, attendees were awarded Certificates of Attendance and Certificates of Completion if they attended the core classes.  

CERTIFICATE OF FARM LABOR MANAGEMENT:  In 2014, a new program was introduced that allows participants to earn a Certificate of Farm Labor Management.   The objective behind this certificate is to enhance the professional stature of those farm labor supervisors who complete the program and successfully manage farm workers in accordance with all associated rules and regulations.   To achieve the Certificate of Farm Labor Management, a total of eight (8) classes are required, and attendees must pass a test administered at the end of each class.  Three (3) of those classes must be Wage & Hour, Human Resource Compliance, and one class related to worker safety.  The remaining five classes will be the choice of the individual.  Times and locations of classes offered in 2016 will be posted at www.swfrec.ifas.ufl.edu , along with registration information. 

Topics are taught at several locations across Florida and in partnership with county extension faculty.  These topics cover laws that keep farm workers safe, fairly paid, and in a working environment free from discrimination and harassment.  The program is offered in both English and Spanish. If there is sufficient interest, individual classes  or combinations of classes can be arranged at times and locations convenient for the participants. We also provide training at grower locations that incorporates grower-specific policies and procedures.  For more information, contact Carlene Thissen, 239-658-3449, carlene@ufl.edu, or Fritz Roka, 239-658-3428, fmroka@ufl.edu.


G. E. Vallad1, T. Jacoby1, N. Boyd1, Z. Guan, and J. Noling2

1 Gulf Coast Research and Education Center, University of Florida, Wimauma, FL

2 Citrus Research and Education Center, University of Florida, Lake Alfred, FL

Text Box: Table 1. Relative vapor pressures and boiling points of the most common commercial fumigants and water.Since the phase-out of methyl bromide (MBr), many vegetable and strawberry growers have observed increasing production losses to nematodes, weeds and various soilborne pathogens. The alternative fumigants, which include chloropicrin (Pic), dimethyl disulfide (DMDS), 1,3-dichloropropene (1,3-D), and several isothiocyanate (ITC) generators that include metam sodium (Vapam), metam potassium (Kpam), and allyl isothiocyanate (AIT), or co-formulations of two to three of these alternatives, are effective, but lack the ability to disperse in soil to the extent of MBr, as a function of their lower volatility.  Volatility is the tendency of any substance to convert to a gas at a given temperature and is directly related to the substance’s specific vapor pressure, which is inversely related to boiling point.  In this case, we are interested in the ability of any fumigant to volatilize from a liquid to a gas once applied to the soil at a soil temperature between 4.4 to 32.2 °C, which corresponds to the 40 – 90 °F soil temperature range specified in most fumigant labels (Table 1).  The vapor pressure and boiling point information for each currently available fumigant is shown in Table 1 and can also be found on the material safety data sheet (MSDS) available for all fumigants.  The vapor pressure values for Pic and 1,3-D are on average ~70-fold less than MBr at 20°C (68°F).  The ITC generators are even less volatile than Pic and 1,3-D with physical characteristics more akin to water; explaining why these products are typically applied with water through drip irrigation systems.  For all practical purposes, MBr was the only true gas used for fumigation, referring to its ability to rapidly volatilize once applied to the soil and quickly fill available airspace within the soil profile, whereas all the current alternatives remain liquid following application and then slowly volatilize. 

Text Box:  Figure 1. Image of side of bed with plastic mulch pulled up to reveal roots emerging below the plastic tuck.Our initial studies focused on field sites where the currently available fumigants failed to manage Fusarium wilt caused by the soilborne fungus Fusarium oxysporum f.sp. lycopersici (FOL).  We observed that most of the field sites having issues with Fusarium wilt were drip-irrigated, and that tomato roots could frequently be found growing along bottom bed edges and below the plastic mulch tuck (Fig. 1).  We hypothesized that the increase in Fusarium wilt was due to the under-fumigation of the soil along the outside edges of beds (referred to as the shoulder) and the soil immediately below the mulch tuck where we often observed root growth. 

Initial experiments, evaluated whether the application of MBr would ‘rescue’ these fields.  Field trials at Gulf Coast REC (Wimauma, FL) and at a grower site (Myakka, FL) demonstrated that the application of MBr:Pic (67:33 or 50:50 formulations at 350 lbs/treated acre) significantly reduced the incidence of Fusarium wilt to an acceptable level compared to the standard application of Pic-Clor 60 (300 lbs/treated acre) (Fig. 2).  At a grower site, the application of MBr:Pic reduced the incidence of Fusarium wilt by 25% to 5% (P<0.05) and increased pack out yields from 4.3 to 7.6 ton/A (P<0.05) compared to the standard Pic-Clor 60 (Fig. 2). In many instances, the recovery of total Fusarium oxysporum from soil cores collected from throughout the bed profile and from the recovery of either FOL or Sclerotium rolfsii from nylon bags that were strategically placed throughout beds immediately following fumigation, demonstrated the inability of the applied Pic-Clor 60 fumigant to effectively disperse throughout the bed compared to a MBr:Pic (67:33) fumigant. 

Text Box:  Figure 2. Image of ‘MBr Rescue’ trial at a grower site, where a 67:33 and a 50:50 formulation of MBr:Pic was applied in strips alongside standard application of Pic-Clor 60 to a field with high levels of Fusarium wilt.In an effort to augment the activity of the standard in-bed application of Pic-Clor 60, a supplemental treatment of Pic was applied along the edges of the raised bed using a Yetter Avenger coulter system.  A pair of coulters were adjusted to straddle each bed, applying Pic100 to a depth of 8 inches below the soil surface, immediately prior to the application of a VIF mulch film (Fig. 3).  Several replicated, strip trials applying Pic100 at 200 lbs/treated acre were established in 2014 and 2015 at a grower site having issues with Fusarium wilt.  Individual treatment plots consisted of 3 beds (34 inch bottom width and 28 inch top width) on 6 foot row spacing at row lengths ranging from 600 to 1400 foot length depending the specific field with drip-irrigation.  Bed fumigation consisted of a standard 8” shank application of Pic-Clor 60 (300 lbs/treated acre).  The supplemental Pic treatment was alternated with non-Text Box:  Figure 3. Photo of Yetter Avenger Coulter system, with a pair of coulters straddling the raised bed. Final application depth is 8” below the soil.treated plots throughout the field (12 plots total) in the spring of 2014 and 2015.  In 2014, the supplemental Pic reduced the incidence of Fusarium wilt by 77% (P< 0.0001), improved yield based on field pack-out by 36%, and nearly doubled root growth at the edge and tuck regions of the bed, based on the dry weight of root tissue recovered at the end of the trial (Fig. 4).  The trial was repeated at the same location in the 2015, the supplemental Pic reduced the incidence of Fusarium wilt by 38% (P=0.0010) and improved yield based on field pack-out by 21%.

Text Box:  Figure 4. Spring 2014 field trial demonstrating the supplemental application of chloropicrin (Pic 100, 200 lbs/treated acre) to bed edges, compared to the grower standard alone (Pic-Clor 60, 300 lbs/treated acre).An additional trial was performed during Fall 2014 to address the supplemental Pic rate on disease incidence and corresponding tomato yields. Trial format was similar to the aforementioned trials, except supplemental Pic rates of 150, 100 and 50 lbs/treated acre were compared to beds treated with just the grower standard Pic-Clor 60 (300 lbs/treated acre).  In addition, since disease levels were lower at this particular grower site, each 3-row plot was 1400 ft long.  Results showed that the supplemental Pic applied at 100 and 150 lbs/treated acre reduced disease incidence by 81% (P=0.0362) and increased pack-out yields by 28% on average compared to the grower standard (P=0.0010).  A repeated field trial in spring 2015 gave similar results. 

Our current recommendations for the supplemental Pic treatment are 125 lbs/treated acre or higher of Pic100.  We do not recommend the use of the EC formulated PicPlus at this time, which is only 85% chloropicrin by weight and contains an emulsifier that may limit volatilization.  Additional trials are also underway to assess whether the overall fumigant rate within the bed can be reduced with the supplemental Pic treatment, to improve overall fumigation costs while maintaining efficacy.

Additional funds have been provided to Vallad, Boyd, Noling and Guan by a federal grant from the NIFA-USDA Methyl Bromide Transition program to establish commercial demonstration trials with growers.  Interested parties should contact Dr. Vallad (gvallad@ufl.edu or 813-633-4121) as soon as possible to begin planning for fall plantings.