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Possible Soil Fumigation Alternatives for Methyl
Bromide in Mulched Tomato Production
J. P. Gilreath and J. P. Jones, University of Florida, Gulf Coast
Research & Education Center, Bradenton, FL 34203; J. W. Noling,
University of Florida, Citrus Research
& Education Center, Lake Alfred , FL 33850; and R. J. McGovern,
Southwest Florida
Research & Education Center, Immokalee, FL 33934.
Fresh market tomatoes, produced on about 50,000 acres and worth up to
$450 million annually, are a major horticultural industry in Florida. Most
of the winter tomatoes consumed in the U.S. come from Florida, where they
are grown on raised, polyethylene mulched beds. Most plants are staked to
improve air movement, which reduces relative humidity and incidence of
foliar disease, and to keep the fruit from contacting the soil which
limits fruit rot. The mild climate and sandy soils which favor crop
production also favor many soil-borne pests of tomatoes and other crops.
Thus, soil fumigation is vitally important in producing tomatoes in
Florida.
The search for fumigant alternatives to methyl bromide for Florida's
tomato production began in 1993. What a handful of Florida scientists
started as fragmented research on various aspects of soil fumigation has
grown into a well-coordinated research and extension program with
participation from the University of Florida, the Florida Tomato
Committee, the Florida Fruit and Vegetable Association, and the USDA-ARS.
Some funding also has been provided by the U.S. Environmental Protection
Agency. Soil fumigant field trials, standardized early on, were conducted
in most of Florida's tomato producing areas, as well as on the main campus
of the University of Florida. We evaluated various soil fumigants for
soil-borne disease, nematode and weed control. It was apparent from early
trials that no one fumigant would control all of the soil-borne pests that
methyl bromide does or as well as methyl bromide.
Nutsedge, both yellow and purple, was one of the most difficult pests
to control for any alternative chemical. Purple was more difficult to
control and more prevalent in tomato fields in the southern portion of the
state where most tomatoes are grown. This weed is capable of penetrating
the polyethylene mulch covering plant beds; since control is difficult
once nutsedge emerges, it, therefore, flourishes without competition.
We evaluated older, registered chemical fumigants as well as some
experimental products and tested efficacy in areas infested with various
important soil-borne pests. These included root knot nematode, Fusarium
wilt, Fusarium crown rot, Southern blight, bacterial wilt, and purple and
yellow nutsedge. Each product had its limitations, some more limited than
others. Telone C-17 provided good control of nematodes and some soil-borne
diseases; whereas chloropicrin controlled diseases well, but not
nematodes. Vapam and Basamid were quite erratic in their performance.
Enzone, an experimental nematicide, failed to control nematodes and
damaged tomato plants in some experiments. Fosthiazate, another
experimental nematicide, controlled nematodes erratically and did not
control other pests. None of the products controlled nutsedge
consistently; in some cases, a few actually increased emergence. It became
evident that nutsedge control would have to be addressed separately with
herbicide. In evaluating these pesticides, we tried to integrate them into
standard tomato production practices of Florida's raised bed,
polyethyelene mulch cultural system. Since this system was designed to use
a liquid fumigant which could be delivered to the soil under pressure
through chisels, liquid fumigants appeared to be easier for industry to
adopt. Vapam, being a liquid, was applied in this manner initially, but
did not perform well. Research was conducted to establish a more
successful application method for Florida's light, sandy soils. Soil
injection with up to 7 chisels in a 36-inch-wide bed was attempted, along
with chemigation through micro-irrigation tubing, and various methods of
spray application and incorporation in the bed.
Our best success has been to spray Vapam on the soil surface,
incorporating immediately with a Rototiller prior to re-shaping the raised
bed and applying polyethylene mulch. But efficacy is still less than
acceptable in most cases. Applying Basamid, a very fine, powder-like,
granular product, is greatly affected by wind which is typically a problem
early in the production season in Florida. Additionally, Basamid efficacy
appears to be highly dependent on soil moisture level at application and
immediately following. Water restrictions in most of Florida's tomato
producing areas eliminate overhead irrigation as an option. Therefore,
Telone C-17 and chloropicrin currently are considered the most
promising alternatives for use in tomato production.
Overall, we found Telone C-17 to be the most consistent and effective
alternative product tested to date; however, nutsedge control requires
the use of a herbicide with Telone C-17. Few herbicides are registered for
use on tomato; few experimental products show promise for this
use. Registered and experimental herbicides have been screened for use on
tomato with Telone C-17. Tillam herbicide has been the most promising
product and is registered for use on tomato. Currently, field trials are
underway on University of Florida research farms and on grower farms to
further define the efficacy of combining Telone C-17 with Tillam to
control major soil-borne pests of Florida's fresh market tomatoes.
[July 1996 Table of
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Last Updated: October 3, 1996
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