Researchers and growers test methyl bromide replacement
By Vicky Boyd
Stuart, Fla., tomato grower Jock Ivy says he's confident he can cut his usage of methyl bromide fumigant in half by using metalized silver mulch that retains more of the gas in the soil.
The 2005 season was the first time he tried the reflective bed covering in cooperative trials with U.S. Department of Agriculture plant pathologist Dan Chellemi.
The results were so good that Ivy con-verted his several hundred acres of tomatoes to metalized mulch for the fall 2006 season. Not only does the reflective bed covering hold in the fumigant longerallowing it to do a better job of killing soilborne pestsbut it also repels virus-carrying whiteflies.
"The reflective does seem to help with insects, and it tends to hold the moisture better," Ivy says. "It's stronger, which means you can stretch it over the beds, and it's easier to work with."
The mulch also saves Ivy money by allowing him to use lower fumigant rates and lengthen his insecticide spray intervals.
Chellemi, who'se based in Fort Pierce, Fla., is experimenting with that same mulch technology and methyl iodide, a soil fumigant from Arysta LifeSciences Corp. of Cary, N.C.The fumigant, trade named Midas, is not yet registered.
But the Environmental Protection Agency issued an experimental-use permit in September 2006 that allows 1,000 acres in Florida, Georgia, Michigan, North Carolina, South Carolina, Tennessee and and Virginia to be treated and the crops sold without restrictions.
The company hopes for a similar program in the Southwest this summer, says Mike Allan, Arysta’s global fumigant product manager.
The Midas formulation being tested is a blend of 50 percent methyl iodide and 50 percent chloropicrin.
A race to find replacements
Part of the impetus behind Chellemi’s work is the fact that methyl bromide will be available only for another three to five years.
Under the Montreal Protocol of 1987, developed nations agreed to phase out the use of ozone-depleting chemicals, including methyl bromide. The countries were supposed to halt all production and use of the products by Jan. 1, 2005.
But a handful of countries, including the United States, said they had no methyl bromide alternatives and successfully sought critical-use exemptions.
For the 2007 season, U.S. growers expect to receive an allocation of 18 percent of 1991 baseline levels, which were 56.3 million pounds.
As the supply of methyl bromide shrinks, the price continues to rise.
“Methyl bromide is going to be around for the next three to five years, but it’s going to be around at much reduced levels,” says Mike Aerts, assistant director of the Florida Fruit and Vegetable Association’s environmental and pest management division in Maitland. “Transition will be the word here. Growers need to have strategies in place that they can fall back on if they can’t get
bromide or all of the bromide they need.”
The EPA also recommends growers use an emission-minimization or barrier film, Aerts says.
Putting the newcomer to the test
In field trials conducted at the U.S. Horticultural Research Laboratory in Fort Pierce, Chellemi is comparing Midas applied under metalized or virtually impenetrable films with the industry standard low-density polyethylene mulch.
Plastic mulch permeability to chemical fumigants is characterized by the amount of fumigant that can pass through a section of film over time. It is reported as grams of fumigant per square meter of film per hour.
In laboratory tests involving an initial concentration of 1,000 parts per million methyl bromide under the film, Chellemi says typical permeability measurements range from about 120 grams per square meter per hour for low-density polyethylene to 13 grams for metalized film and 0.2 grams for VIF.
Although he says growers may not need to go to the extreme of using VIF, he says they need to consider improved barriers because of increasing environmental concerns.
Chellemi’s trial also involves three rates of Midas—180 pounds, 150 pounds and 120 pounds per treated acre. Each plot is 75 feet long, and each treatment is replicated four times.
“We want to see how low a rate we can use and still get [pest] control,” he says.
Pacific Ag Research of San Luis Obispo, Calif., used the patented Symmetry machine to apply the fumigant.
Once the beds were fumigated and plastic applied, peppers and tomatoes were planted. Throughout the trial, Chellemi and his technician, Nick Rotindo, will rate weed control in the plots.
“Unfortunately, there was some variability in nutsedge control with the lowest rate under the VIF,” Chellemi says about early weed counts.
They hope to be able to harvest a crop and evaluate fruit yield and quality.
How do alternatives pencil out?
Arysta recommends 150 pounds of product per treated acre when used with metalized film or VIF, Allan says. In fields with 36-inch beds and 6-foot centers, Chellemi says growers actually will apply 75 pounds of Midas per acre because they only treat the beds, not the row middles.
At $10 per pound, the chemical cost would be $750 per acre.
VIF and metalized plastic film run about $220 to $245 per 4,000-foot roll of 60-inch-wide plastic, according to an informal survey Chellemi conducted in December 2006.
If growers use a standard low-barrier film, they will need to increase the rate to 300 pounds of Midas per treated acre, Allan says. High-density polyethylene that is 0.75 mil thick runs about $190 per 6,000-foot roll, according to Chellemi’s survey.
Having a Symmetry rig apply the fumigant is not required, but is recommended, Allan says. “It provides greater accuracy in terms of rates per acre and reduced rates per acre, and greater protection for workers and the environment,” he says, adding the rig can be used for any fumigant.
Adapting to a 50-50 methyl bromide blend
The Midas price compares with methyl bromide, which currently sells for about $3.70 per pound for a 50-50 mixture of bromide and chloropicrin, Chellemi says.
“The problem with 50-50 is that growers need to make sure they have applied enough methyl bromide to achieve nutsedge control,” Chellemi says.
In the past, when the fumigant was 67 percent bromide and 33 percent chloropicrin, he says growers were able to cut fumigant rates in half from 350 pounds per treated acre to 175 pounds by using metalized mulch or VIF. Methyl bromide constituted about 116 pounds of that mixture.
With the new blend, which has less actual methyl bromide, Chellemi says the half rate would mean only 82 pounds of bromide per treated acre. So growers will need to bump up the amount of fumigant they use to ensure nutsedge control.