MeBr Alternatives and Their Current Limitations in Florida

James P. Gilreath, University of Florida, Gulf Coast Research and Education Center, Bradenton, Florida

While there are many limitations to the adoption of methyl bromide alternatives in Florida, those limitations are much different from the principal ones in California in that they are not State regulatory driven, at least not at this time. Telone products, including Telone II (1,3-dichloropropene) and Telone C-17 and Telone C-35 (mixtures of 1,3-dichloropropene and chloropicrin), constitute the most likely replacements for methyl bromide in many crops in Florida, including vegetables and ornamentals.

Large-scale trials have demonstrated these products on grower farms, especially tomato farms. One of the main obstacles for adoption of alternatives is nutsedge control, and most of the currently available alternatives either provide no control or erratic performance in Florida soils. Tillam has been identified as a herbicide which can be used in conjunction with Telone to provide nutsedge control; however, it is only labeled in tomato and has produced crop damage in some cases. In general, it is felt that these instances of phytotoxicity were the result of improper application or inadequate soil incorporation, as performance has been acceptable in most of the large-scale trials conducted on grower farms. Tomato growers are fortunate in this regard for they have an effective herbicide; however, there are many crops where herbicide options are few, including pepper, eggplant, and cucurbits like watermelon.

Ornamental growers, such as producers of caladiums and cut flowers, have seen little research on their crops and thus are much farther behind tomato and pepper in the selection and development of alternative strategies.

Telone products have two problems, and these are shared by some of the other alternatives: excessive personal protective equipment (PPE) requirements and setback or buffer space requirements. Buffers of 300 ft. from occupied structures are not a problem for most tomato growers, but for the bulk of the Florida strawberry industry, they are a major deterrent. Most of the production is situated in the Plant City area of Florida. Plant City has become a bedroom community of one of our largest cities, Tampa, and berry fields are generally located within what has become residential areas. Some fields have housing developments on three sides and a road on the fourth. The average strawberry field is 20 acres or less. The arable area of a 20-acre field gets very small when a 300-ft. buffer is imposed, and even smaller if it is interpreted as commencing not from the actual dwelling but from the property line. Thus, Florida strawberry growers do not feel that Telone products are a viable alternative for them. Telone may be efficacious and result in good fruit production, but the buffer may render it impractical for berry growers.

While all seems positive for tomato growers, they do share a common problem with other producers who may rely on Telone products, and that is the PPE issue. The use of a full-face respirator, rubber gloves, and boots and coveralls all but kills any chance of Telone being used in Florida, especially during the fall season. Our tropical to subtropical climate makes it extremely difficult to work in the required PPE, and heat stress becomes a major issue. Realistically, heat stress may not be a problem because workers are not likely to work under those conditions; thus the real problem would be an inability to fumigate soil for crop production and the resultant economic hardship the grower would experience.

In an effort to deal with or circumvent the PPE issue, those of us working in Florida have investigated broadcast application as an alternative to in-bed application of Telone products. Broadcast application would involve one person in an air-conditioned tractor cab with appropriate PPE and carbon filtration of recirculating air, thus greatly reducing the impact of PPE to a manageable level. While this sounds like a good idea, little data exist for the efficacy of Telone and chloropicrin mixtures when applied to nonbedded soil without polyethylene mulch covering it.

This launched a new wave of research activity wherein broadcast was compared to in-bed applications of Telone C-17 and C-35. Telone II (1,3-D) has been applied broadcast or in-bed without mulch in potatoes for years, and nematode control efficacy has been well documented. The real question was not so much whether Telone (1,3-D) would work, but rather whether chloropicrin would work under nonmulched conditions. There was some concern that the higher vapor pressure of chloropicrin would allow it to escape too quickly to kill pathogenic fungi near the soil surface.

Several large-scale trials were conducted on grower farms, and disease control appeared to be comparable between the two application methods, but anecdotal information suggested that some diseases may not be controlled as well as Fusarium wilt race 3 appeared to be controlled in these trials. Results of small-plot experiments with tomato last fall and again this spring demonstrated that disease control could be compromised. As a result, most grower trial applications now consist of Telone II or Telone C-35 broadcast with additional chloropicrin applied to the soil in the bed at the time of bed formation. Some cases exist where the application of chloropicrin both broadcast and in-bed is beneficial.

Broadcast application appears to be the answer to the PPE issue, but it in itself introduces other potential problems. In order to make the application, allow sufficient time for the product to work and dissipate, then re-enter the treated field, form beds, and wait for the dissipation of chloropicrin, a grower must allow at least 3 weeks for what once required 10 days to 2 weeks with methyl bromide. Summer, when fumigant is being applied for fall production, is the time wherein most of the rainfall for the year occurs in peninsular Florida. This can greatly disrupt soil fumigation activities and result in even greater delays in planting in August and September, thus making it more difficult for growers to develop and adhere to any type of production schedule.

During December, January, and early February, when soil fumigants are applied for the spring crop, soil moisture often is low and this extra time for fumigation increases irrigation water needs by increasing the time over which it is necessary to maintain field moisture at the point required for good biological activity. Since growers are budgeted by the water management districts for water consumption, this reduces the quantity of water available for use by the crop.

The spring production season is Florida's dry season and rainfall is sparse; thus growers rely heavily on well water for irrigation during what is the largest production season. If the pre-wet period is too short, soil-borne pests may be inactive and more difficult to kill, and fumigant failure can occur. This was the situation on several farms in Florida this spring, and rootknot nematodes were a problem even in fields fumigated with methyl bromide. If a grower uses too much water for initial land preparation and fumigation, he may exhaust his permitted quantity before the crop is ready for harvest.

One of the big advances to come out of the broadcast application effort has been the tremendous improvement in application equipment. Previous equipment left much to be desired and resulted in erratic performance in some trials. Many different pieces of equipment were tried before the ultimate winner would be identified.

Today, all broadcast applications in research trials in Florida are being made with what is known as the Yetter rig. This equipment, manufactured by Yetter Equipment Co., consists of a series of 30-inch coulters with a forward-swept knife or chisel behind each one with a small "beaver tail" on it, and behind that rolls a set of press wheels which seal the soil surface. The coulters are positioned 1 foot apart. This equipment was pioneered in Florida by John Mirusso, who first saw it at a farm show in the northeast where it was being used for delivery of liquid manures.

Use of this equipment has resulted in much more uniform results and improved efficacy. One of the big advantages of the Yetter rig is that it places the Telone about 12 inches deep where nematodes may escape the effect of the more typical 6 to 8 inch deep applications. In addition, it does not drag plastic mulch and string around a field creating large chisel tracks and the resultant loss of fumigant. Instead, the coulter cuts through this and other debris and provides a more narrow kerf which is easier to seal.

While we have worked a lot on minimization of the impact of PPE by developing broadcast application of Telone, we also have investigated application of fumigants through the drip irrigation system as a means of improving delivery and handling and reduction of worker exposure and the negative implications of PPE requirements.

Applications through drip irrigation tubing would not only reduce the impact of PPE by reducing the number of people involved and allow development of a closed delivery system, but it also would allow fumigant delivery for "double cropping" where the old polyethylene mulch and drip tubing are being used for a second crop in the same beds.

Drip application of any fumigant is a challenge in Florida's sandy soils. Most of our production soils are classified as fine sands with less than 1 percent organic matter, no clay, and very little silt. These soils tend to be droughty and do not favor lateral movement of water or other liquids.

Several years ago drip delivery of Telone was attempted in research trials in Florida and it was not successful. Since that time we have studied the delivery and distribution of water via drip irrigation tubing and have a much better understanding of the downward and lateral movement of water in beds and have investigated multiple tubes, adjuvants, water volumes, pressures, and run times to understand what might improve the delivery of a water-soluble pesticide in our soils.

We now feel we can achieve better results than in the past, but one obstacle still remains: weed control in the bed.

While Telone may provide the nematode control we need, it will not control weeds like nutsedge. We still need a herbicide or some other product which can give us this control. Metam may be an option for our weed control needs, but its performance has been erratic in past research in Florida, and the one thing growers require of any alternative is consistency.

Much research has been conducted on the application of metam in Florida, recognizing that proper application was the key to improved efficacy. Decreased chisel spacing, high-pressure injection, disk incorporation, rototiller incorporation, delivery through the drip irrigation system, and many other techniques have been investigated, but the one which has been the most efficacious has been rototiller incorporation followed by either immediate bed formation or power rolling the soil surface to seal it.

Drip irrigation delivery has resulted in narrow bands of nutsedge control in the past, but just as was true with Telone a lot depends upon the actual mechanics of the application and we still have a lot to learn. Drip delivery would be more acceptable to most growers if we could improve efficacy, because rototillers are slow, require a lot of horsepower, and few growers own one.

A few growers who have experimented with metam application on a broadcast basis followed by bed formation soon afterward have complained about the fumes and had problems getting their labor to stay on the job. At least one Florida grower is using it in this fashion. Overall, we still have work to do to improve application technology for metam.

A final problem identified with metam is the volume of product required per acre and the need for delivery and storage facilities for a large farm. One hundred acres of tomatoes would require 7,500 gallons of metam, and that is a lot of product to handle. Application through the drip irrigation system would make that a more manageable task, but storage and delivery problems would still exist to some extent. Hopefully, there will not be any surprises in the form of PPE or buffer zones for metam or chloropicrin when they go through re-registration.

Chloropicrin's future is tied to partnering with Telone for the most part, as alone it is not considered an effective nematicide and provides poor to no weed control. While it is an excellent fungicide for soil-borne pathogens, soil-borne pest control needs are seldom only diseases and are usually a complex of disease with nematodes or weeds or all three combined.

While there are other products being considered as potential alternatives, Telone and chloropicrin are the most likely immediate successors to methyl bromide. Lack of enough data, efficacy problems, and the lack of handling experience with many of these other products make them less likely to become common "household words" in the near future.

The last impediment I would like to discuss is what I call a grower's "comfort level." I asked two of my best tomato grower cooperators if they were comfortable with Telone C-35 plus Tillam herbicide. Each told me the same thing: "I have seen it in your experiments each season here on my farm for at least the last 5 years and the results have been good. I don't think we have had any problems with it or lost much production, if any, but when you ask me if I am comfortable with it, I have to say I am not. I know what methyl bromide will do because I have used it for many years and there is a lot to be said for the short time interval between application and planting and the wide range of conditions under which I can apply it and still get acceptable control. Use of Tillam makes me nervous because I am not used to applying a herbicide, and my experience with herbicides has been to kill things and I have even damaged tomatoes with it. Am I comfortable with this as an alternative? No. That does not mean that I cannot become comfortable with an alternative, but right now I am not comfortable with this and will have to ease into it slowly."

Comfort is that feeling we have from knowing something well. This level of knowledge is only attained through prolonged exposure and positive experiences. Comfort will not come overnight, and any negative experience can set back the progress made to date tremendously. This is why as scientists we must try to anticipate the problems and address them before they reach the grower. Additionally, we need to work closely with growers to introduce them to the alternatives we recommend and any other new technology associated with their use to assure an easy transition so there are viable alternatives with which our growers feel comfortable. Only then is our job complete.

Last Updated: July 17, 2002