Horticultural Sciences Department

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Issue No. 601

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
May 2015

New ilarvirus species identified in south Florida tomatoes

Christian Miller, UF/IFAS Palm Beach County Extension

Gene McAvoy, UF/IFAS Hendry County Extension

Scott Adkins, USDA ARS USHRL Fort Pierce, FL 

Over the past four years solanaceous crops have been extensively surveyed in the southern half of Florida for the emerging thrips-transmitted tospoviruses, Tomato chlorotic spot virus (TCSV) and Groundnut ringspot virus (GRSV).  USDA-ARS scientists testing submitted samples have shown that TCSV and GRSV are both currently present in south Florida, along with the well-known Tomato spotted wilt virus (TSWV).  Something puzzling occurred in 2013, when symptomatic tomato plant and fruit samples did not test positive for any of these tospoviruses. 

Field collection of symptomatic tomato samples has been coordinated and implemented by Glades Crop Care, Inc., with the cooperation of many growers, other scouting organizations, University of Florida/IFAS Extension and researchers, and USDA-ARS scientists in Fort Pierce.  Samples were typically collected from plants showing necrotic lesions, chlorotic spots, and/or ring spots on leaves, stems, petioles or fruit.  

It was surprising to have symptoms of virus-like necrosis on leaves, petioles and stems, and necrotic rings or spots on fruits similar to those induced by TCSV and GRSV yet the sample not test positive for either virus.  Further testing by scientists at FDACS-DPI and USDA-ARS eliminated all of the usual tomato virus suspects known in Florida.  Eventually, a new ilarvirus species was identified for which the name Tomato necrotic streak virus (TomNSV) is proposed.  Symptoms, as seen in Figures 1 and 2, of TomNSV in the field have been reproduced by inoculation of greenhouse tomato plants with symptomatic field samples.

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TomNSV is a distant relative of Tobacco streak virus (TSV), which is the cause of bean red node disease in south Florida and has been detected in each of the last several seasons in the Belle Glade and Homestead, FL farming regions.  TSV and other ilarviruses are reported to be transmitted by thrips but in a manner quite different from the TCSV, GRSV and TSWV tospoviruses. 

Now that TomNSV has been identified, scientists have been able to test other previously collected samples for this new virus.  TomNSV has subsequently been detected in similarly symptomatic tomato samples collected from the spring and fall seasons of 2014 in Palm Beach County.  No detections have been made in 2015.  During the initial TomNSV findings in fall 2013, incidence of symptoms was generally low (<3%), although >1000 plants were rogued from a single Miami-Dade County farm.  The lack of TomNSV detection so far in 2015 may be due to TCSV or Tomato yellow leaf curl virus

(TYLCV) outbreaks in Miami-Dade and Palm Beach County locations (from where TomNSV was originally detected) that are obscuring symptoms.  No natural hosts for TomNSV other than tomato have been identified to date.  An FDACS-DPI Specialty Crop Block Grant is funding current studies to examine other hosts for both TomNSV and TSV, and to determine the mode of transmission of these viruses in Florida.  No matter what the ultimate economic cost of TomNSV to the Florida tomato industry, its detection through pest surveys and definitive identification as a new virus highlights the importance of vigilant crop scouting.


New Technology for Vegetable Production (III) IST Summary

G. David Liu1, Frederick Fishel2, and 3Kelly Morgan

1Horticultural Sciences Department, 2Agronomy Department, and 3Soil and Water Science Department, IFAS, University of Florida

Vegetable grafting, 4R nutrient stewardship, and other new techniques have been developed for vegetable and fruit production. These new techniques from both Florida and other states can improve profitability of Florida’s crop producers and sustainability of the environment. The objective of this IST was to enhance the productivity, profitability, and sustainability in commercial crop and fruit production and minimize negative impacts on the environment. This program and a CEU roundup were conducted and Polycommed from Gainesville to 15 host sites statewide on March 25, 2015.  Five extension specialists were invited for this IST training.

Dr. Joshua Freeman discussed 1) new mulch film technology, totally impermeable film (TIF), containing multiple polymer layers that change film permeability; 2) TIF increases fumigant concentration in the soil environment; 3) this increases the effective dose and protects bystanders from offsite fumigant movement and hence, allows for significant reductions in soil fumigant use rates while maintaining pest control efficacy; and 4)  each of these adds significantly to the tools available to producers.

Dr. Joseph Noling 1) summarized the current regulatory situation and requirements governing use of soil fumigants in Florida; 2) discussed the research conducted to economically evaluate differences in pest control efficacy and crop yield of a diversity of soil fumigants;  3) described new fumigant application, flow metering/distribution systems, and plastic mulch installation methodologies required for low rate fumigant applications; and 4) documented the importance of traffic pans (soil compacted zones) as impediments to downward movement of soil fumigants and as a contributing cause to pest control inconsistencies.

Dr. Steve Phillips, North American Program Director for the International Plant Nutrition Institute (IPNI), introduced 1) agricultural production strategies that best combine the economic, social, and environmental expectations of stakeholders, so-called “best management practices” (BMPs); 2) fertilizer use BMPs aptly described as the application of “4R Nutrient Stewardship”, applying the right fertilizer source at the right rate, right time, and in the right place; 3) these four “rights” comprehensively convey how fertilizer applications are managed; 4) determining what is “right”, however, depends on site-specific factors including soil, climate, crop, management system, and logistics.

Dr. Sanjun Gu, Extension Specialist at North Carolina A&T State University, discussed 1) vegetable grafting greatly enhances disease resistance, cold hardiness, and yield for extended production in greenhouses and high tunnels; 2) presented the practice of vegetable grafting in the United States; 3) stated that, as disease-free soil declines due to the phase-out of fumigant methyl bromide, vegetable grafting would provide a good option for protection from soil-borne diseases; 4) briefly covered the history of grafting, grafting methods, grafting research updates in the United States, and the resources for vegetable grafting.

Dr. Steve Sargent presented 1) fruit and vegetable growers and handlers often unnecessarily experience significant losses during harvest and handling operations; 2) these losses can be outright unmarketable, but more often and more subtly, they are losses in grade – still marketable, but fetching a lower price; 3) the principles behind practical methods for maintaining highest quality produce; 4) quality parameters, harvest maturity, field and consumer containers and cooling were all covered.

Links to the instructors and Powerpoint presentations given at the event are below:

Dr. Joshua Freeman, Improved Plastic Mulch Technology and New Fumigant Chemistries for Soil-Borne Pest Management

Dr. Joseph Noling, New Technologies to Study the Biology and Management of Plant Parasitic Nematodes

Dr. Steve Phillips/International Plant Nutrition Institute, 4R Nutrient Stewardship for Florida Agriculture

Dr. Sanjun Gu/North Carolina A&M State UniversityVegetable Grafting, an Emerging Practice for American Vegetable Growers 

Dr. Steve Sargent, Postharvest Handling for Quality and Freshness

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