The million dollar question

04/01/2008 02:00:00 AM

Strawberry trials seek long-term economic methyl bromide replacements

By Vicky Boyd

Four soil fumigants all appear to work well in strawberry fields that have been historically treated with methyl bromide to suppress soil-borne diseases, weeds and nematodes.

What remains unknown is how they will work in four to five years when the residual effects of methyl bromide have worn off and soil-borne pest populations have begun to climb, says Shawn Crocker, executive director of the Plant City-based Florida Strawberry Growers Association.

“That’s really the million dollar question,” Crocker says. “A lot of these products work really well here after methyl bromide because the [pest] populations of hardened seed and disease have been reduced. Three to five years is when these products will really start to show whether they provide control because they are not following methyl bromide anymore.”

Crocker is in the second year of a large-scale field trial at the association’s Plant City facility comparing four fumigants with methyl bromide, which has been the grower standard for decades.

The 1987 Montreal Protocol changed that by classifying methyl bromide an ozone-depleting chemical and developing a phase-out for its use. The international treat required developed countries to cease production and use of the fumigant by 2005, whereas developing countries have until 2010 to completely phase out its use.

In both cases, the protocol allows for critical-use exemptions should alternative not be available. U.S. growers, including the strawberry industry, have successfully petitioned for critical-use exemptions the past three seasons.

In search of the Holy Grail
The Florida strawberry trials are part of a continuing effort within agriculture to find viable replacements for the widely used fumigant.

Crocker has five replicates on the 10-acre parcel near Dover, Fla. Although his trial involves a mixture of 98 percent methyl bromide and 2 percent chloropicrin, some growers have resorted to 67-33 (67 percent methyl bromide and 33 percent chloropicrin) since the 98-2 is more difficult to find.

He also is overseeing five trials in growers’ fields comparing methyl bromide to a 50-50 blend of methyl iodide and chloropicrin, marketed as Midas by Arysta LifeScience Corp. of Cary, N.C.

Midas has been used under a non-crop-destruct experimental use permit in Florida, Georgia, Michigan, North Carolina, South Carolina and Virginia since 2006. About 1,000 acres are involved.

The company received an EUP for about 30 acres in California in 2007.

The Environmental Protection Agency granted Arysta a 1-year registration for Midas in late 2007, and 27 states also have registered the product. Registration is pending in Florida, and it is not registered in California.

“Methyl iodide works very well,” Crocker says. “Its only problem is the iodine part is extremely expensive.”

Methyl bromide runs about $3.10 per pound, or about $465 per treated acre, he says. Midas was initially priced at $10 per pound, and Crocker used it at 175 pounds per acre. Because growers typically treat only the bed, the cost per treated acre will be less.

Since the product received full registration, the price has dropped to $8 per pound, according to Arysta.

With the full registration of Midas, growers can expect to see a significant price reduction, says Mike Allan, Arysta global product manager for the fumigant. The actual price will vary among distributors.

“With the EUPs, you were talking about limited acreage and small volumes that you have to produce, and that’s always more costly,” Allan says.

Nevertheless, he says Midas will still command a 20 percent to 30 percent price premium over methyl bromide.

All of the beds within Crocker’s strawberry trials are covered with Pliant Blockade, a virtually impenetrable 1.25-mil film that reduces the amount of gas that can permeate the plastic. The material costs about twice as much as the 1-mil low-density polyethylene that growers traditionally have used, Crocker says.

University of Florida researchers also will rate the trials for plant health and weed control.

The smell of success?
Crocker has separate trials that look at a combination of dimethyl disulfide, marketed as Paladin by Arkema Inc. of Philadelphia, and chloropicrin. Paladin was applied at 74 gallons per treated acre.

The Environmental Protection Agency has not yet registered Paladin, although it granted Arkema a non-crop-destruct EUP for 200 acres in Florida, Georgia and North Carolina.

Initial Paladin trials at the association’s facility during the 2006-07 season looked promising enough to prompt Crocker to expand them this year.

“I think it has a lot of promise because the components are very cheap,” he says.

DMDS, which smells like rotten eggs, is a byproduct of petroleum manufacturing and onion processing. Among its uses is an odorant in natural gas.

During the first year, Crocker says he learned to wait at least 24 hours after punching holes in the plastic to allow the gas to dissipate before transplanting young strawberry plants. Otherwise, the plants may be stunted because DMDS is a much slower moving gas than methyl bromide.

“Other than that, the control was outstanding,” he says.

Time will tell
Carl Grooms, manager of Fancy Farms Inc. of Plant City, volunteered a 1 1/2-acre plot of virgin ground to test Paladin and Midas during the 2007-08 season.

“The nutsedge just totally ate us up, so we went in and pulled the nut grass plants out so we can have a crop,” Grooms says. “Compared to methyl bromide, that’s going back 50 years ago.”

Using a hand weeding crew would be too costly for commercial fields, he says.

Outside of the nutsedge problems, Grooms and Crocker say the crop appeared to be growing and producing well in mid-January. The real test comes near the end of the season.

“We want to continue to watch the tests for a couple of months from now to see whether we get infestations of soil-borne disease and nematodes,” Grooms said in mid-January. “By the end of March or mid-April, if infestations take over, I can tell you.”

Allan blames Grooms' nutsedge control problems on less-than-optimum soil conditions during fumigation. Arysta has conducted numerous trials with Midas and other fumigants on virgin ground for up to four years with much different results, he says.

“There’s a marked difference on what’s going to be a viable crop, as with Midas, and what’s going to be a problematic crop, as with the alternatives,” Allan says.

Grooms also has a 10-acre Midas trial on strawberry ground that’s been historically fumigated with methyl bromide. In that trial, nutsedge is not a problem.

“Any farmer on existing ground that has been farming could get by with any of these alternatives for a couple of years,” Grooms says. “But every year he farms, the problems will build up. So these tests need to be done for four to five years to see how bad things can get.”

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