Florida growers have been coping with the gradual phaseout of methyl bromide for years as researchers desperately seek an alternative that will perform as well as the fumigant—or even close to it.
In Florida, methyl bromide has been used on tomatoes, peppers, eggplant, strawberries and a handful of other crops.
In 1996, methyl bromide was classified as an ozone-depleting substance by the Montreal Protocol on Substances that Deplete the Ozone Layer, and an international body called for its phaseout.
Today, use is limited to slightly more than 4 percent of the baseline year, 1991. That will drop to about 2.5 percent by 2013, says Andrew MacRae, assistant professor of weed science at the University of Florida’s Gulf Coast Research and Extension Center in Wimauma.
“It’s almost gone,” he says. Until three years ago, methyl bromide was used for tomatoes in a mixture of 67 percent methyl bromide, which fights most soilborne pests, and 33 percent chloropicrin, which is active against soilborne diseases.
Today, methyl bromide is only sold in Florida as a 50/50 combination, which disappoints growers.
“We have a lot of soilborne disease issues with tomatoes,” MacRae says. “We just don’t get the control that we used to see with 67-33.”
Methyl bromide on the way out
About the only place methyl bromide is still used is in the Miami-Dade area, where other fumigants pose a threat to the water table because of the soil type.
Methyl bromide alternatives are used elsewhere. But MacRae emphasizes that just because something may be referred to as an alternative doesn’t mean it works as well as methyl bromide.
“There is nothing in our testing or in the grower experience where we can say across the board that it is just as good as methyl bromide,” MacRae says.
For awhile, a combination of methyl iodide plus chloropicrin—sold under the trade name Midas—was used as an alternative. But the manufacturer, Arysta Life- Science, voluntarily pulled the registration in March “based on its economic viability in the U.S. marketplace,” the company said. The product was too costly to produce, MacRae surmises.
MacRae, however, has developed two-way and three-way chemical combinations that have provento be effective substitutes— depending on where they’re used.
The two-way combination consists of about 40 percent Telone and 60 percent chloropicrin.
It’s sold as a premix from Tri-Est under the name Pic-Clor 60, or growers can use the two products separately, either in the same pass or individually in two passes. The combination is excellent on nematodes and good on diseases, but only fair on weed control, MacRae says.
So you’ll have to take additional weed control measures, such as adopting a fallow program that includes glyphosate and using herbicides under the plastic mulch. You may even need to apply an herbicide over the top of the mulch before planting, depending on weed pressures.
This controls yellow and purple nutsedge that might germinate and pierce through the mulch.
Once the tomato crop has emerged, you can use the herbicide Sandea to help control nutsedge.
The three-way combination uses Telone, chloropicrin and either metam potassium (trade names KPam and Sectagon K54) or metam sodium (trade names Vapam and Sectagon 42).
Telone is effective for nematode control and some weed control; chloropicrin for disease control and some weed control; and metam potassium or metam sodium for weed control, some disease control and some nematode control.
Metam potassium or metam sodium can be shanked into the bed about 4 inches deep or applied through drip tape irrigation—but both processes are challenging in Florida’s sandy soil beds, McRae says.
Overall, he estimates that the two-way combination can be up to 85 percent as effective as methyl bromide, and the threeway combo can be 95 percent as effective.
But those numbers are not as impressive as they may seem.
“You’re talking about millions of weed seeds and billions of nematodes and individual cells for diseases,” MacRae says.
With a 5 percent to 15 percent reduction in effectiveness annually, the number of pests and incidences of diseases will increase each year, he says.
With the fallow program, additional herbicides and impermeable mulches, fumigating a field now can cost $1,000 more than in the past, he says.
Ruskin-based DiMare Ruskin Inc. has phased out methyl bromide everywhere except in the Homestead and south Dade County areas, where alternatives can’t be used because they impact the water tables, says Scott DiMare, farm operations manager.
The company uses methyl bromide only on about 1,500 acres of tomatoes. The company previously used it for peppers, cucumbers and other commodities, as well.
DiMare currently uses a 50/50 ratio of methyl bromide and chloropicrin, which he says is “not nearly as effective” as the 67/33 ratio growers previously used.
In other areas, he uses Pic-Clor 60*#151;a combination of chloropicrin and Telone—as a substitute for methyl bromide, but neither that nor anything else DiMare has used is as effective as methyl bromide.
“We’ve been through all the products,” he says.
As the residual effects of methyl bromide wear off, DiMare says, “You’re going to have a lot of weed problems and soilborne disease problems.
“We’ve got more fusarium this year than I’ve ever seen in places that we’ve never had it before.”
And he expects to see more southern blight, as well.
Crystsal Snodgrass, a University of Florida Extension vegetable specialist in Palmetto, says growers suffered a 14 percent greater crop loss without the use of methyl bromide.
Full impact unknown
It may be five years before the full impact of the loss of methyl bromide is realized, MacRae says.
In the meantime, the industry needs to build a cultural program of fumigant application, maintain proper soil conditions to maximize fumigant efficacy and use additional pesticides to control weeds, diseases and nematodes to keep fields clean and profitable, he says.
“Unfortunately, all these pieces do not currently exist,” MacRae says. “They will be developed, and we will eventually get there, but it will take time.”