Horticultural Sciences Department

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Issue No. 608

The Vegetarian Newsletter 

A Horticultural Sciences Department Extension Publication on 
Vegetable and Fruit Crops 

Eat your Veggies and Fruits!!!!!

Publish Date: 
December 2015/January 2016

Watch Out for Outbreaks of Tomato Chlorotic Spot Virus (TCSV) in South Florida

Shouan Zhang, Tropical Research and Education Center, UF/IFAS

Qingren Wang, UF/IFAS Miami-Dade County Extension

Dakshina Seal, Tropical Research and Education Center, UF/IFAS

Gene McAvoy, UF/IFAS Hendry County Extension

In November 2015, initial symptoms of Tomato chlorotic spot virus (TCSV) were observed in a number of commercial tomato fields in Homestead, Florida. On November 17, 2015, a survey conducted in a few fields indicated that TCSV was present on large round tomatoes (cv. ‘Sanibel’, ‘FL 47’, and ‘Ridge Runner’) as well as plum tomatoes (cv. ‘Mariana’), ranging in age from 3 to 6 weeks after transplanting. Initial symptoms appeared on plants approximately 3 weeks after transplanting. In general, the incidence of the disease was low, however, up to 0.5-1% plants showed the symptoms of TCSV. However, it reached as high as more than 50% in a few commercial tomato fields in a survey conducted on December 22, 2015. Populations of thrips were high in area vegetable fields that were planted to tomato, snapbean, squash, eggplants, and other crops. Samples were collected from tomato fields and brought to the laboratory to check for thrips.  Common blossom thrips (Frankliniella schultzei) a vector of TCSV were identified in the samples, along with other thrips species including melon thrips (Thrips palmi) and Florida flower thrips (F. bispinosa).

Due to the warm weather this season, populations of thrips are still multiplying. Severe outbreaks of TCSV are likely due to the occurrence of the disease and the presence of large thrips populations. Growers should be alert for potential outbreaks of this devastating disease in tomato, particularly in South Florida. In addition, attention must be paid to the potential spread of this virus to central, northern Florida and even other neighboring states in the spring season.      

TCSV was first reported in tomato plants from South Florida in 2012. Tomatoes infected with TCSV typically develop necrotic lesions, chlorotic spots, and ring spots on leaves, stems, petioles, and fruit (Fig. 1). Following the initial symptoms, wilting and bronzing of the infected plants may occur.  Infection of TCSV in young tomato plants may result in severe stunting and eventually death of the plant (Fig. 2). Like Tomato spotted wilt virus (TSWV), TCSV is a tospovirus exclusively transmitted by flower thrips. Western flower thrips (Frankliniella occidentalis) and common blossom thrips are known vectors of this tospovirus. The fact that the disease is occurring more widely with greater frequency throughout South Florida is a cause for concern.

During the growing season of 2014, South Florida experienced the first outbreak of TCSV, causing significant economic losses to tomato growers.  In some fields in Homestead, Florida, up to 30% tomato plants were infected and rogued. In worst cases, the entire planting was abandoned due to infection with TCSV (Fig. 3). 

Currently, there are no strategies established and available for management of TCSV. The close relationship between TCSV and TSWV indicates that integrated management strategies directed against TSWV may also be effective for control of these new tospoviruses. Research at the UF/IFAS Tropical Research and Education Center (TREC) indicated that resistance to TSWV seems to confer resistance/tolerance to TCSV from trials conducted in Miami-Dade County (Fig. 4). Research in North Florida has demonstrated that a combination of UV reflective mulches, acibenzolar-S-methyl (Actigard), and insecticides has provided excellent management of TSWV in commercial tomato fields. Field trials to evaluate the effects of these strategies on TCSV are underway in Miami-Dade County.  

Results from a field trial conducted at TREC UF/IFAS in spring 2015 indicated that Radiant (spinetoram) and Exirel (cyantraniliprole) significantly reduced disease incidence of TCSV 45 days after transplanting compared to the untreated control. Radiant and Exirel-treated plants had fewer adults of common blossom thrips than the untreated control 4 weeks after transplanting.  Mean numbers of western flower thrips adults were significantly lower in the plots treated with Radiant, Exirel, Malathion, Brigade, Lannate alt. Requiem, Agrimek alt. Exirel, and Malathion alt. Radiant than the untreated control.  Due to high disease pressure in this trial (95% of plants were infected in the untreated plots), a repeat of the trial is on-going in Homestead, FL during the fall season, the regular tomato production season.

In Miami-Dade County, tomato growers have reported increasing problems with tospoviruses transmitted by thrips during the past few growing seasons. An integrated management approach that combines the use of effective insecticides such as Radiant and Exirel to control flower thrips and to reduce thrips larval development, thus limiting secondary virus spread, should prove effective in reducing the disease of TCSV. Research in Florida has indicated that insecticides alone may not be adequate to control the virus. Integrated approaches have to be taken into consideration for success in management of this disease, particularly in South Florida.  

For more information, see ENY859- Managing Thrips and Tospoviruses in Tomato at http://edis.ifas.ufl.edu/in895.

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Figure 1. Symptoms of TCSV in tomatoes

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Figure 2. Stunting of plant growth due to TCSV infection

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Figure 3. Tomato planting abandoned due to infection with TCSV

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Figure 4. Disease of TCSV on TSWV-resistant tomato varieties. cv. ‘FL 47’, a commercial standard cultivar as a control


Article #16 - THE IMPORTANCE OF TRAINING

Many of us at UF/IFAS conduct trainings on a regular basis.   Sometimes our educational message may seem to be rote and the importance of what we are sharing may be forgotten, but every now and then something happens that reminds us why we do what we do. 

A recent article from the Associated Press described a bus accident in Arkansas in which six migrant workers were killed.   It turned out the driver worked for a Florida company.   There was no indication that the driver was intoxicated; however there may have been other.contributing factors.  As part of Farm Labor Supervisor Training, we teach a class on the Rules & Regulations for Drivers and Safe Driving.  When accidents occur and workers are hurt, we sometimes think:   “If they had just attended this training….”  Perhaps the driver would have double-checked his tire tread to better handle bad weather, or thought about getting more sleep the night before, or restricted his drive time to the legal limit of ten hours. Simple reminders sometimes are needed to reinforce proper safety behavior. Other safety training that we do in conjunction with UF Cooperative Extension Agents include Pesticide Safety, Agricultural Equipment Safety, First Aid and CPR.  

The training we conduct in Florida has an effect all over the country, not just in Florida, particularly up and down the East Coast and Midwest migrant worker streams.    We are working on a study to see how many companies and crew leaders annually migrate out of Florida and where they travel to during the spring and summer months.  The results will likely show a significant number, just based on observing worker pick-up locations after the spring harvest.   All the workers they supervise, whether Florida workers or in other states where the crew leaders work, are affected by training done here.  

We teach other topics in addition to safety as part of the Farm Labor Supervisor Training program.  For example, Wage & Hour classes teach rules and regulations that keep farm workers treated fairly and paid correctly.   We also have a class on Discrimination and Harassment, with a particular focus on sexual harassment, to keep people in the fields and groves protected.   

In addition to convincing farm supervisors to do the right thing for its own sake, a little knowledge from a training program could result in a significant financial savings for growers, farm labor contractors and crew leaders.   The U.S. Department of Labor – Wage and Hour Division recently announced an increase in their Civil Monetary Penalties to a minimum of $1,000.   As an example of this financial impact, consider a single missing item on the Terms & Conditions of Work Form (WH-516), which prior to this year could have carried a penalty as low as $50. Now, a single omission from the 516-form could cost as much as $1,000 per worker.  If that particular 516-form was given to a crew of 40 workers, the farm labor contractor could be facing a fine as much as $40,000.   Under Joint Employment, the grower can be held liable for these fines whether or not the labor contractor can pay.  We cannot say that completing any training program will eliminate all regulatory violations and fines. We can say, however, that training will make one more aware of the regulations and provide some basis to set policies in place to avoid violations.   

Authors:   Thissen, C.; M.T. Bayer, F.M. Roka.  

Carlene Thissen and Fritz Roka work for the University of Florida at the Southwest Research and Education Center, Immokalee, FL, 239-658-3400.  carlene@ufl.edu.  Mike Bayer is a former DOL-WHD Investigator, now with Curran, Bayer & Associates, West Palm Beach, 561-371-0126 mtbayer@curranbayer.com  

DO YOU HAVE QUESTIONS RELATED TO FARM LABOR MANAGEMENT RULES AND REGULATIONS?   Please email carlene@ufl.edu and we will try to get your questions answered.