Horticultural Sciences Department

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Issue No. 589

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
March 2014

Laurel Wilt in Avocados—History, Current Strategies and a Look to the Future

Jeff Wasielewski
Commercial Tropical Fruit Agent
Miami-Dade County, UF IFAS
jwasielewski@ufl.edu
305-248-3311, ext. 227

A battle is being waged in the avocado groves of South Florida where the region’s largest and most economically important fruit crop is under attack. Avocados are produced on approximately 7500 acres in Miami-Dade County and have an economic impact of $54 million to the regional economy (Crane, 2012). The avocado industry has already lost over 2500 trees due to laurel wilt since the introduction of the disease to Miami-Dade County in 2011.

Laurel wilt is disease that affects plants in the Lauraceae causing rapid wilt and sudden death. It is caused by a fungus, Raffaelea lauricola, that was accidentally introduced, along with its original vector, the redbay ambrosia beetle, Xyleborus glabratus, to the United States in May of 2002 in Port Wentworth, Georgia. (Crane, 2012).

Trees become infected when female ambrosia beetles carrying Raffaelea lauricola bore into a host tree in order to create a gallery to purposely cultivate the fungus as food for their young. Once infected, the tree begins to wall off its vascular tissue as a defense mechanism. This unfortunate strategy effectively interrupts all water and nutrient transport in the phloem of the infected areas and causes rapid mortality of the infected tree.

While it was originally thought that the redbay ambrosia beetle was the only vector of this disease, it is now known that there are currently six ambrosia beetles, in addition to the redbay ambrosia beetle, that are known to carry a sufficient quantity of Raffaelea lauricola to infect native species in the Laureace. Two of those species are known to cause infection in avocado (Carrillo, 2013). It is not known how much of a role the additional ambrosia beetle vectors play in the spread of the disease. It is important to note that redbay ambrosia beetles will bore into healthy trees while the existing native and exotic ambrosia beetles typically bore into weak or damaged trees.  

Symptoms of the disease in avocados include large areas of the tree’s upper canopy rapidly wilting and turning brown. The leaves die so quickly that they remain on the tree and are unable to fall. Other symptoms include a discoloration of vascular tissue and bore holes on the trunk next to tiny sawdust straws.(Figure 1 and Figure 2) If a tree is suspected to have laurel wilt, a sample should be taken from the tree and sent for testing so it can be positively identified and distinguished from trees that exhibit similar symptoms such as trees struck by lightning, trees distressed due to fruit load or trees infected with Phytophthora.

Current Recommendations

Once an avocado tree in infected with laurel wilt, there is no known remedy to save the tree. A tree that has been positively identified as infected tree should immediately be removed by cutting down the tree and removing and destroying the tree’s stump. The resulting debris should not be transported as it likely contains infected beetles. Debris should immediately be destroyed through chipping. The wood chips and adjacent trees should be treated with Malathion immediately to kill any remaining beetles. The stump is often difficult to destroy because of its size and is sometimes burned on site. (Figure 3 and Figure 4) Any contact the infected tree had with adjacent avocado trees in the grove through root grafting should be severed by trenching as the disease is thought to spread via root graft.

It is also recommended that a ring of two trees in each direction adjacent to the infected tree within the grove be treated through injection or infusion with the fungicide propiconazole to discourage the spread of the disease. (Figure 5) Propiconazole and its method of application is cost prohibitive, but it is currently the only registered fungicide that has shown promise in protecting adjacent trees. Comprehensive research studies on other more economically feasible and long lasting fungicides are currently underway.

If infected trees are not quickly removed and properly disposed of, the disease will rapidly advance through the grove.

The Future

Laurel wilt continues to advance and new strategies are necessary to lessen the economic blow of the continued loss of trees due to this disease. Current methods being assessed for the future include the use of detector dogs and or drones to scout for the disease, using spectral cameras to locate positive trees before they show visible symptoms, looking at cultural care and its role in the spread of the disease, genetic resistance, and using traps and baits in combination to thwart the movement of the beetles. Aerial helicopter surveys are already currently being used to locate infected trees to locate symptomatic trees.(Figure 6 and Figure 7)

At present, there is no silver bullet for stopping the advance of laurel wilt as it continues to produce an economic toll on avocado growers, Miami-Dade County and the state of Florida. It is only through continued research, scouting and persistent removal of infected trees that we can hope to lessen the effect of this devastating and economically impactful disease.(Figure 8)

References:

Crane, J. 2012. Current status and recommendations for control of laurel wilt and the redbay ambrosia beetle. http://trec.ifas.ufl.edu/RAB-LW-2/pdfs/Current%20status%20and%20recommendations%20for%20control%20of%20LW%20and%20RAB%204-10-13%20pdf%20version.pdf.

D. Carrillo, R. E. Duncan, J. N. Ploetz, A. F. Campbell, R. C. Ploetz and J. E. Peña. 2013. Lateral transfer of a phytopathogenic symbiont among native

and exotic ambrosia beetles. Plant Pathology.

Figures:

Figure 1: Vascular Discoloration

Figure 2: Sawdust Straw

Figure 3: Removed Stump

Figure 4: Woodchips

Figure 5: Infusion Port

Figure 6: Detector Dog

Figure 7: Drone

Figure 8: Laurel Wilt Mortality


Using Hydrogen Cyanamide in Low Chill Peaches

Dr. Mercy Olmstead, Stone Fruit Extension Specialist, UF Horticultural Sciences Department, Gainesville, FL

In subtropical fruit crops, especially low-chill peaches, chill unit accumulation is an important variable that growers often track to determine if their trees receive enough cool temperature exposure during the winter months.  Why is this important?  Temperate fruit trees require a certain amount of chill accumulation during dormancy to resume normal growth in the spring.  This is often referred to as the chilling requirement which is unique to each cultivar and can often be tracked as accumulated chill units using a model that is specific for certain crops. 

In peaches, we use a modified Utah Chill Model where one chill unit is accumulated between the temperatures of 37-48 °F (Richardson et al., 1974).  For temperatures that are above or below this ideal threshold, 0.5 or even zero chill is accumulated (Table 1).  If the trees do not get the required amount of chill for a specific variety, poor or uneven budbreak, poor flowering, delayed foliage emergence and poor fruit set can occur, hindering commercial success (Erez, 1987; Saure, 1985).  Thus, previous research has targeted methods that “break” the dormancy cycle and induce budbreak in seasons with low chill unit accumulation. 

Table 1.  Modified Utah Chill Unit Model for ‘Redhaven’ and ‘Elberta’ Peaches.

Hydrogen cyanamide is a chemical used in several perennial fruit crops as a “rest-breaking” agent, most notably Florida blueberries.  It is a restricted use pesticide that can be quite dangerous if improperly handed.  Users should always follow the label directions, which includes very specific directions for handling, mixing and applying hydrogen cyanamide.  Hydrogen cyanamide must be applied using an enclosed cab tractor for the applicator’s safety.  Growers use this chemical to induce foliar budbreak that coincides with bloom and fruit set (Williamson et al., 2002).   An added benefit of hydrogen cyanamide is a shortened fruit development period, which can help berry growers harvest earlier to take advantage of higher market prices.  In peaches, research conducted in Australia showed that proper dormant application advanced the harvest date of ‘Flordaprince’ by 10 days (George et al., 1992).   However, hydrogen cyanamide has not been routinely applied to low-chill peaches in Florida.  Thus, the objective of this preliminary study was to investigate lateral budbreak percentage, terminal budbreak percentage and shoot dieback as affected by two rates of hydrogen cyanamide applied before bloom in Southeast Florida. 

Materials and Methods

Experiments were conducted on 5-year-old trees of ‘UFSun’ and ‘UFOne’, located in southeast Florida.  Hydrogen cyanamide (Dormex®, AlzChem, Germany; 50% a.i.) was applied at two rates, 2 and 3% (v/v) in ‘UFSun’, while only 3% was applied in ‘UFOne’.  A surfactant was used (Silwet L-77, Helena Chemical Company, Collierville, TN) and trees were sprayed at a rate of 125 gpa.   A control was also included in which no chemical was applied.  Treatments were applied on December 17-18, 2013, approximately 3 weeks before anticipated budbreak.  No additional information about temperature or presence of dew was recorded.  Lateral and terminal budbreak and shoot dieback (%) were tracked on February 7, 2014 (N=5). 

Data were statistically analyzed using JMP (v. 11, SAS Institute, Cary, NC).  Least square means were used to determine differences using Tukey’s HSD (p<0.05).  Error bars were determined by using the standard error of the mean. 

Results and Discussion

The application of hydrogen cyanamide was effective at increasing lateral budbreak in both ‘UFSun’ (Figure 1), and ‘UFOne’ (Figure 2).  There was no difference between the 2 and 3% rates in ‘UFSun’, indicating that a lower rate is as effective as the higher rate.  Hydrogen cyanamide requires significant worker protection and can result in severe illness if improperly exposed (de Haro, 2009).  Thus, application of the lowest effective amount would be considered a best management practice.  Terminal budbreak (%) was not affected in ‘UFSun’; however ‘UFOne’ trees that received hydrogen cyanamide application (3%) had significantly more terminal budbreak (77.8%) than those that did not receive the application (1.3%; p<0.001). 

Neither rate in either variety significantly affected shoot dieback percentage (p>0.05), indicating that there is no significant phytoxicity associated the higher rate of 3%, at the particular stage of application (3-4 weeks before anticipated budbreak). 

Figure 1.  Effect of hydrogen cyanamide at 0, 2, or 3% rates on the lateral budbreak of ‘UFSun’.  Letters denote mean separation as determined by Tukey’s HSD (p<0.001).  Error bars indicate the SE of the mean. 
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Figure 2.  Effect of hydrogen cyanamide (3% rate) and a control on the lateral budbreak of ‘UFOne’.  Letters denote mean separation as determined by Tukey’s HSD (p<0.001).  Error bars indicate the SE of the mean. 

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Figure 3.  Peach orchard without (left) and with Dormex ® applied.  Image taken February 17, 2014, courtesy of Ryan Atwood (KeyPlex). 

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Orchards that received hydrogen cyanamide were visibly more advanced in regards to lateral budbreak and leaf emergence (Figure 3).  It also advanced terminal budbreak and bud swell in a variety that was vastly under chilled (i.e., ‘UFOne’). 

At this point, the limited data that we have is encouraging, and we hope to be able to fund further research on a larger scale in 2014-2015.  We will track fruit harvest dates, yield and fruit size to see if these variables are affected. 

In conclusion, the application of hydrogen cyanamide can be tested in the orchard to improve lateral budbreak and uniformity of bloom in early maturing, low-chill peach varieties.  However, great caution must be taken to avoid damage to the flowers and vegetative buds, which can occur if applications are made too close to budbreak.  If buds are swelling, do not apply hydrogen cyanamide.  Many blueberry growers have severely reduced their crop by spraying too late or at rates higher then recommended.  If growers or agents have questions, please direct them to Mercy Olmstead (mercy1@ufl.edu). 

References:

de Haro, L. 2009. Disulfiram-like syndrome after hydrogen cyanamide professional skin exposure: Two case reports in france. Journal of Agromedicine 14:382-384.

Erez, A. 1987. Chemical control of budbreak. HortScience 22:1240-1243.

George, A., J. Lloyd, and R. Nissen. 1992. Effects of hydrogen cyanamide, paclobutrazol and pruning date on dormancy release of the low chill peach cultivar Flordaprince in subtropical Australia. Australian Journal of Experimental Agriculture 32:89-95.

Richardson, E.A., S.D. Seeley, and D.R. Walker. 1974. A model for estimating the completion of rest for 'Redhaven' and 'Elberta' peach trees. HortScience 9:331-332.

Saure, M.C. 1985. Dormancy release in deciduous fruit trees. Horticultural Reviews 7:239-300.

Williamson, J.G., G. Krewer, B.E. Maust, and E.P. Miller. 2002. Hydrogen cyanamide accelerates vegetative budbreak and shortens fruit development period of blueberry. HortScience 37:539-542.


New Technology for Vegetable Production IST Summary

G. David Liu1 and Frederick Fishel2

1Horticultural Sciences Department and 2Agronomy Department, IFAS, University of Florida

Considerable research has been focusing on biochar and its properties in recent years. Due to its nature, biochar significantly increases cation exchange capacity, enhances nutrient use efficiency, reduces nutrient leaching and offers improved defense against plant pathogens. Thus, biochar may have potential to become a BMP tool for crop production. However, biochar is still new to our crop production industry. To effectively use biochar in crop production and better manage nutrients in sandy soil in Florida, we invited the biochar specialist, Dr. Johannes Lehmann from Cornell University and UF-IFAS extension specialists to gather and share their expertise in enhancing economical and environmental sustainability at an In-service Training. The training was based in Gainesville and was broadcast statewide to 15 host sites via polycom on February 26, 2014. Dr. Mark Ritenour presented the techniques to minimize decay of fruit and vegetable products. Dr. Wenyuan Song summarized the advances in resistance genes and plant diseases. Dr. Donald Dickson showed the most recent characteristics desired in nematicides, and presented interesting biological facts of nematodes. Dr. Kati Migliaccio shared smart irrigation schedules such as “Do it myself” scheduling, site specific smart hardware scheduling, and web and app scheduling tools. Some county faculty and Dr. Migliaccio discussed the possible application of smart irrigation tools to strawberry production in north Florida after the presentations were completed. Dr. Clyde Fraisse’s student, Verona Montone presented agroclimate disease tools including strawberry advisory systems, and a citrus copper application scheduler. The training offered FDACS CEUs for licensed applicators.

Below are links to presentations from the IST training-- New Technology for Commercial Vegetable Production (II):

·         Dr. Mark Ritenour – Maximizing Fresh Fruit & Vegetable Quality

·         Dr. Johannes Lehmann (University of Cornell) – Biochar and Soil Health

·         Dr. Wenyuan Song – Plant Immunity vs. Disease Control

·         Dr. Donald Dickson  – Status of Plant Pathogenic Nematode Management in Southern USA

·         Dr. Kati Migliaccio – Smart Irrigation Practices to Promote Plant Defense against Diseases

·         Miss Verona Montone and Dr. Clyde Fraisse – AgroClimate Disease Tools

This IST training was video recorded and is available online. A table of contents with a complete listing of the topics and hyperlinks to those topics are also available at:

 http://hos.ufl.edu/faculty/gdliu/service-training

Prediction of Controlled-release Fertilizer Nitrogen Release in Seepage Irrigated Tomato Production in Florida

Monica Ozores-Hampton, Luther C. Carson, Jerry Sartain and Kelly Morgan

The Federal Environmental Protection Agency and Florida Department of Environmental Protection have recognized the importance of water quality through the implementation of the Federal Clean Water Act of 1972 and the Florida Restoration Act of 1999 (Bartnick et al., 2005). The Federal Clean Water Act Section 303(d) requires identification of impaired water bodies and establishment of total maximum daily loads (TMDLs) for pollutants that may enter water bodies while maintaining the designated use (Environmental Protection Agency, 2009).  Florida best management practices (BMPs) are a voluntary series of production practices that help the vegetable industry meet the TMDLs by minimizing nutrient and sediment runoff (Bartnick et al., 2005).  Furthermore, BMPs may be implemented individually or as a group but they need to be “technically feasible, economically viable, socially acceptable, and based on sound science” (Bartnick et al., 2005).

Traditionally, split soluble fertilizer (SF) applications, fertigation, and enhanced efficiency fertilizers (EEF) are used to increase N use efficiency (NUE) in tomato production.  Enhanced efficiency fertilizers are a group of fertilizers that reduce the risk of nutrients loss to the environment and subsequently increase NUE (Slater, 2010).  Increases in NUE can be accomplished by maintaining nutrients in the root zone through reduced solubility, thus retaining nutrients in a reduced leachable form using nitrification inhibitors or physical barriers (e.g. fertilizer coating) (Trenkel, 2010).  There are three subgroups of EEFs with different characteristics for horticultural crop production systems. 

Slow-release fertilizers (SRFs) contain N in a less-soluble plant-unavailable form that usually needs microbial degradation to become plant available N (Figure 1).  Stabilized fertilizers are SFs applied concurrently with a chemical inhibitor to slow the bacterial oxidation of ammonium (NH4+) to nitrate (NO3-) or to slow the enzymatic transformation of urea to NH4+ (Trenkel, 1997).  Controlled-release fertilizers (CRFs), the last subgroup of EEFs, are usually urea, ammonium nitrate, potassium nitrate or other SF coated with a polymer (polyethylene and ethylene-vinyl-acetate or thermoplastics), resin (a subgroup of polymers and refers as alkyd-type resins and polyurethane-like coatings), sulfur, or a hybrid of a polymer coating over a sulfur coated urea (Figure 1).  These coated materials release nutrients in water at a predictable temperature-dependent rate (Trenkel, 2010).  Slow-release fertilizer and CRF are recognized in the Florida Vegetable and Agronomic Crops BMP manual (www.floridaagwaterpolicy.com) as a nutrient management BMP. Controlled-release fertilizers may allow for a single fertilizer application if the release pattern is well understood, but are more costly than conventional SFs. 

Figure 1. Methylene-urea slow release fertilizer (left) and b. Polymer-coated controlled-release fertilizer (right). Credits: Monica Ozores-Hampton

The majority of the tomato production in the main production areas of south Florida use subsurface or seepage irrigation consists of managing a perched water table above a slowly permeable soil layer (hard pan) located at 30 to 60-inches below the surface.  Ground or surface water is pumped into canals or ditches, which moves horizontally between adjacent ditches (spaced 50 -75 ft).  When waters from adjacent ditches meet the water table rises, thereby irrigating the crop from the hard pan to the soil surface. The water table may be raised to near the soil surface as a frost protection measure (Ozores-Hampton et al., 2011).   In tomato production systems using subsurface (seepage) irrigation, fertilizer is placed at bed formation as a bottom (cold mix) and a top (hot mix) mix (Simonne and Hochmuth, 2010).  The bottom mix will be placed prior to false bedding, and the top mix will be placed in two bands on the shoulders of the bed after bed formation (Simonne and Hochmuth, 2010).  The bottom mix contains all the P and micronutrients, and 10% to 20% of the N and K, while the hot mix contains the remainder of the N and K.  The University of Florida/Institute of Food and Agricultural Sciences (UF/IFAS) recommended nutrient rates for tomatoes are 200 N, 0 to 150 P2O5, and 0 to 225 K2O lbs/acre depending on soil test results (Simonne and Hochmuth, 2010).  With the exceptions of leaching rain events (3 inches of rainfall in 3 days or 4 inches in 7 days), extended season, and low leaf tissue N and K concentrations or petiole sap NO3- and K test result SF must be applied at bed formation (pre-plant) for plasticulture tomato production using seepage irrigation (Cantliffe et al., 2006).  After occurrence of one of the exceptions, supplemental fertilizer can be applied using a fertilizer injection wheel or by punching holes in the polyethylene mulch by hand. 

Several factors influence nutrient release from CRFs including soil temperature, moisture content, osmotic potential, nutrient composition, coating thickness, and prill diameter. Manufacturers of CRF manipulate the nutrient release duration of resin-coated fertilizer, polymer-coated fertilizer (PCF), and polymer sulfur-coated urea (PSCU) by adjusting by coating thickness and composition, with thicker coatings having longer release durations (Carson and Ozores-Hampton, 2013).  However, in irrigated vegetable production, soil temperature may be considered the most influential factor (Carson and Ozores-Hampton, 2013). 

Controlled-release fertilizer manufacturers such as Agrium Advanced Technologies Inc. (Loveland, CO), Everris Intl. (Dublin, OH), and Chisso-Asahi Fertilizer Co. (Tokyo, Japan) and Florikan ESA LLC. (Sarasota, FL) determine nutrient release duration in water at a constant 20.0, 21.1, and 25.0 °C, respectively (Agrium Advanced Technologies, 2010; Everris, 2013; Florikan, 2012a and 2012b).  However, the average daily soil temperatures under a polyethylene-mulch covered, raised vegetable bed in south Florida were greater than 79.2 °F for eight weeks after bedding and were as high as 104.2 °F during the daytime in a fall tomato season (Table 1) Carson et al., 2012; Carson et al., 2013).  Thus, high soil temperatures during the fall will affect CRF release duration used in tomato production.  Therefore, selection of an incorrect CRF release duration results in slow nutrient release causing plant nutrient deficiencies, low plant growth, and reduced yield, or a high nutrient release rate may result in increased soil electrical conductivity, plant toxicity and injury, and the loss of CRF benefits (Shaviv, 1996). 

In this study we used the pouch method to measure the field N release of the CRF, which  consists of a known mass of CRF (e.g., 0.12 ounces N) sealed inside fiberglass mesh pouches that were buried at a 4-inch depth inside a polyethylene mulched tomato bed and removed at pre-arranged dates (Figure 2).  Tomatoes were planted 18 days after bedding and were irrigated with seepage irrigation.  After collection, the N content remaining in the CRF prills was measured to determine the amount of N remaining and release rate. 

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Figure 2. Tomato field controlled-release fertilizer pouch and temperature data logger installation in Immokalee, FL. Credits: Monica Ozores-Hampton

Table 1. Summary of minimum (Min.), average (Avg.), and maximum (Max.) soil temperature at 4 inches below the bed surface and air temperature in Immokalee, FL during Fall 2011.

Nitrogen release from pouch-incubated CRFs in the tomato field was accelerated during the fall season as compared to the manufactures stated release (Table 2).  A nonlinear regression fit all CRF’s N release (R2 ≥ 0.94). Based on these results, polymer coated urea - 120 day release (PCU120)  may release similarly to polymer coated urea - 180 day release (PCU180) and could extend nutrient release by 16 days compared to a 90 days duration release CRF. Tomatoes take up 10% and 30% of the season total N in the first 30 and 46 days after transplant, respectively (Scholberg, 1996).  Thus, a 120 or 180 days release CRF should be considered as a viable option for fall seepage irrigated tomatoes compared to a 90 day release CRF.

Table 2. Nitrogen (N) release from controlled release fertilizers (CRFs) incubated in pouches during a 129 days fall 2011 tomato season in Immokalee, FL (Carson et al., 2013). 

Laboratory methods can allow CRF incubation in controlled environmental conditions compared to field incubations.  Laboratory methods such as standard and accelerated temperature controlled incubation method (STCIM) and ATCIM, respectively, may be used to compare CRFs and to quickly screen CRFs.  These methods may be used to predict laboratory release, but will not predict field release when used alone.  Controlled release fertilizer nutrient release differs in free water, water saturated sand, and sand at field capacity (Du et al., 2006).  Thus, laboratory incubations without correlation can offer only restricted practical use for commercial vegetable production because the results will not reflect nutrient release obtained under field conditions.  There are two types of methods based on release time.  The so-called STCIM can be used for CRF specified nutrient release time or until a threshold amount of nutrients (e.g., 75%) released (Dai et al., 2008; Du et al., 2006).  The ATCIM of CRF can be used in shorter time (e.g., 74 h) at a higher temperature than the standard methods (Dai et al., 2008; European Committee for Standardization, 2002).  There are variations in both methods, each designed to test CRF using selected time periods, temperatures, and/or sample collection methods. 

This study used an ATCIM method develop by Sartain et al. (2004a and 2004b) that can predict the nutrient release from some CRFs and SRFs after column incubation with up to 90% accuracy (Figure 3).  When a line is fitted to the column incubated fertilizers release data, it follows the equation:

% Nutrient Released = a - b * e - ct

“Where ‘a’ equals the mean values of percent N released when time equals zero, ‘b’ equals the slope of the function or the mean rate of increase in N released over time, ‘c’ equals the maximum level of N released or the asymptote, ‘e’ equals the natural logarithm and ‘t’ equals time” (Sartain et al., 2004a). 

If an accelerated TCIM could be used to predict CRF field release, then it may assist growers with CRF management decisions in tomato production. 

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Figure 3. An accelerated temperature controlled incubation unit as described by Sartain et al. (2004). Credit: Luther Carson

The ATCIM and field pouch method predicted field N release from the individual CRFs in polyethylene mulched tomato production for most CRFs with an R2 ≥ 0.90.  Thus, an ATCIM may be used to predict CRF field release after correlation with a field pouch study.  Further investigations are being performed to predict CRF N release in the field without performing pouch studies. 

As part of the BMP program in Florida, CRF has the potential to reduce the environmental impact of tomato production fertilizer practices.  However, adoption of CRF relies on research demonstrating reduced N rates, similar or increase marketable tomato yield and postharvest fruit quality.  An ATCIM or pouch field method that determines the ability of a CRF fertilizer program to meet the tomato N requirements may help identify those CRFs. Thus, these tests may provide growers with an additional tool to assist and facilitate with the adoption of CRF as part of BMP in vegetable production. 

Literature Cited

Agrium Advanced Technologies. 2010. DurationCR: Controlled-release fertilizer. 29 Aug. 2013. <http://agriumat.com/includes/duration_sell_sheet.pdf>.

Bartnick, B., G. Hochmuth, J. Hornsby, and E. Simonne. 2005. Water quality/quantity best management practices for Florida vegetable and agronomic crops. Florida Dept. Agr. Consumer Serv., Tallahassee, FL.

Cantliffe, D., P. Gilreath, D. Haman, C. Hutchinson, Y. Li, G. McAvoy, K. Migliaccio, T. Olczyk, S. Olson, D. Parmenter, B. Santos, S. Shukla, E. Simonne, C. Stanley, and A. Whidden. 2006. Review or nutrient management systems for Florida vegetable producers: A white paper from the UF/IFAS vegetable fertilizer task force. Proc. Fla. State Hort. Soc. 119:240-248.

Carson, L.C. and M. Ozores-Hampton. 2013. Factors Affecting Nutrient Availability, Placement, Rate, and Application Timing of Controlled-Release Fertilizers for Florida Vegetable Production using Seepage Irrigation. HortTechnology 23:553-562.

Carson, L.C., M. Ozores-Hampton, and K.T. Morgan. 2012. Effect of controlled-release fertilizer on tomatoes grown with seepage irrigation in Florida sandy soils. Proc. Fla. State Hort. Soc. 125:164-168.

Carson, L.C., M. Ozores-Hampton, and K.T. Morgan. 2013. Nitrogen release from controlled-release fertilizers in seepage-irrigated tomato production in south Florida. Proc. Fla. State Hort. Soc. 126:In Press.

Dai, J., X. Fan, J. Yu, F. Liu, and Q. Zhang. 2008. Study on the rapid method to predict longevity of controlled release fertilizer coated by water soluble resin. Agr. Sci. China 7:1127-1132.

Du, C., J. Zhou, and A. Shaviv. 2006. Release characteristics of nutrients from polymer-coated compound controlled release fertilizers. J. Polym. Environ. 14:223-230.

Environmental Protection Agency. 2009. Clean Water Act Section 303. U.S. Environ. Protection Agency, Washington, DC.

European Committee for Standardization. 2002. Slow-release fertilizers: Determination of the of the nutrients-method for coated fertilizers. European Committee for Standardization, Brussels BS EN 13266:2001.

Everris. 2013. Osmocote classic. 29 Aug. 2013. <http://www.everris.us.com/sites/default/files/e90551_.pdf>.

Florikan ESA. 2012a. Technologies & brands-Florikan. 29 Aug. 2013. <http://florikan.com/flktech.html>.

Florikan ESA. 2012b. Technologies & brands-Nutricote. 29 Aug. 2013. <http://florikan.com/nuttech.html>.

Ozores-Hampton, M.P., E.J. McAvoy, M. Lambert, and D. Sui. 2011. A survey of the effectiveness of current methods used for the freeze protection of vegetables in South Florida. Proc. Fla. State Hort. Soc. 123:128-133.

Sartain, J.B., W.L. Hall, R.C. Littell, and E.W. Hopwood. 2004a. Development of methodologies for characterization of slow-release fertilizers. Soil and Crop Sci Soc of Florida Proc 63:72-75.

Sartain, J.B., W.L. Hall, R.C. Littell, and E.W. Hopwood. 2004b. New tools for the analysis and characterization of slow-release fertilizers. p. 180-195. In: W.L. Hall and W.P. Robarge (eds.). Environmental Impact of Fertilizer on Soil and Water. American Chemical Society.

Scholberg, J. 1996. Adaptive use of crop growth models to simulate the growth of field-grown tomato. University of Florida, UMI, PhD Diss. 9800184.

Shaviv, A. 1996. Plant response and environmental aspects as affected by rate and pattern of nitrogen release from controlled release N fertilizers. p. 285-291. In: O. Van Cleemput, G. Hofman and A. Vermoesen (eds.). Progress in Nitrogen Cycling Studies. Kluwer Academic Publishers, Netherlands.

Simonne, E.H. and G.J. Hochmuth. 2010. Soil and fertilizer management for vegetable production in Florida. In: S.M. Olson and B.S. Santos (eds.). Vegetable production handbook for Florida. IFAS/UF, Gainesville, FL.

Slater, J.V. 2010. Official Publication AAPFCO. Association of American Plant Food Control Officials, West Lafayette, Indiana.

Slater, J.V. 2010. Official Publication AAPFCO. Association of American Plant Food Control Officials, West Lafayette, Indiana.

Trenkel, M.E. 1997. Controlled-release and stabilized fertilizers in agriculture. IFA, Paris, France.

Trenkel, M.E. 2010. Slow- and controlled release and stabilized fertilizers: an option for enhancing nutrient use efficiency in agriculture. 2nd ed. IFA, Paris, France.