Without methyl bromide, vegetable growers are working harder to achieve similar results from substitute fumigants.
"Methyl bromide was special," says Joe Noling, professor of nematology at the University of Florida's Citrus Research and Education Center in Lake Alfred. "Replacing it was a challenge."
Growers have several fumigant choices but the new materials require more management and are more affected by moisture, temperature and other environmental conditions, says Gary Vallad, associate professor of plant pathology at the University of Florida's Gulf Coast Research Center in Wimauma.
To get the best results from methyl bromide substitutes, "You've got to be on your game," says Stanley Culpepper, Extension agronomist in weed science at the University of Georgia in Tifton.
Culpepper helped develop Trifecta, a mixture of Telone II (1,3-dichloropropene), chloropicrin and dimethyl disulfide (DMDS). He, Vallad and Noling also are seeking ways to make the new fumigants more efficient and easier to use. Trifecta achieves that by putting three fumigants into a single application cylinder.
"Methyl bromide was idiot-proof," producing acceptable results under all conditions, says Scott DiMare, director of farm operations for DiMare Fresh Inc., in Homestead. "Now all these little mistakes show up and show up big time."
DiMare has tested most methyl bromide alternatives and has settled on Pic-Clor 60 (a mixture of 1,3-dichloropropene and chloropicrin) as his best bet so far.
"Some have better weed control, some are better with disease," he says. "The problem is nothing is consistent."
Diseases and weeds that methyl bromide once kept in check now are emerging, from persistent problems with nutsedge to increasing outbreaks of charcoal rot and Fusarium.
"Some fumigants don't even faze it," Noling says of charcoal rot.
"We're starting to see Fusarium in places we never have before," DiMare says. Crown rot, or southern blight, is another rising concern.
"The further we get away from methyl bromide, the more of these that are going to peek out,” he says.
Weeds continue as top pest
Weeds are the main ongoing problem for Georgia growers, Culpepper says.
"Usually when we have a problem, we missed nutsedge. But that was also an issue with methyl bromide," he says.
Trifecta is effective on nutsedge, but does little against annual grasses and broadleaf weeds.
"In almost all situations, growers are going to have to use herbicides," Culpepper says. That means learning how to apply herbicides in raised-bed plasticulture.
Mistakes there can place a double dose around the crop and none in parts of the bed where growers want weed control.
"A lack of pest control is bad, but herbicide injury is unacceptable," Culpepper says.
Refocusing on application methods
Solutions lie not only in the fumigants themselves, but in application methods. Growers now use a plasticulture system originally developed for methyl bromide, Vallad says.
Changing bed architecture now is impractical, so the focus must turn to how best to apply methyl bromide substitutes into beds, he says.
The new materials have lower vapor pressures than methyl bromide, making them far less volatile; that restricts their movement and levels across the bed. Soil temperature and moisture also can hinder their movement even more.
Vallad plans tests this spring of applying additional fumigant outside the bed. The extra treatments along bed edges should help reduce Fusarium recolonization.
DiMare is partnering in those tests. "We're losing three to four weeks on crops" from Fusarium, a span that can cut out one entire picking, he says. "That's a big deal. Hopefully this will save us those few weeks."
Meanwhile, Bielinski Santos, associate professor of horticulture at the Gulf Coast research center, is testing a different approach with drip irrigation, to see if surfactants might improve lateral fumigant movement.
But local soil types may limit the use of irrigation as an application method, Noling says. "Our soils are not conducive
(to the practice) without leaving a significant portion of the bed untreated," he says.
Most of the new fumigants are mixtures, often with chloropicrin as a base. "We're cocktailing three (materials) to achieve what we did with methyl bromide," Noling says.
Georgia growers have relied mainly on the UGA three-way system, applying Telone II, metam sodium and chloropicrin under a low-density polyethylene mulch.
It's not perfect, Culpepper says, but it's proved effective, especially for spring applications.
To control nutsedge and nematodes, he recommends Paladin Pic (a mixture of DMDS and chloropicrin) combined with a high-barrier mulch. Paladin does have odor issues, however.
The potential for odor complaints requires additional management when used near residential areas.
Noling points to 500 acres treated last year with DMDS in 5-acre increments, where a GreenStar GPS system triggered precision application equipment on and off. Impermeable plastic was laid over the treated acreage for odor retention.
Despite all those precautions, official odor complaints still numbered 38 -- and, he says, likely many more unofficial complaints circulated as well.
New products in the pipeline
Vallad has tested Dominus, a bio-fumigant containing allyl isothiocyanate, or oil of mustard, and currently is working with Nimitz (fluensulfone), a nematicide from MANA applied to the soil before planting.
Several field trials showed Dominus provides "fairly good efficacy" against low to moderate levels of weeds, Vallad says.
Nematode and disease control were similar to other methyl bromide alternatives.
Dominus doesn't have a strong vapor phase, however. Its best fit may be for small- to medium-sized operations, he says.
Vallad also sees promise in Trifecta, especially if the manufacturer moves into custom blends to reduce odor issues and to better handle different weather conditions.
"But the question for us is, “Will it handle our nematode and soil disease issues? Vallad says.
All the new fumigants cost less than the current price of methyl bromide -- where it's available, Culpepper says.
But that's only part of the equation.
"The bottom line is how are the crops responding? Our yields are going down," DiMare says. "Are you able to maintain a consistent yield?"
Inconsistent results make calculations even harder, he says.
Ultimately that will shake out the industry. Growers will "either get better at it or get out," Di Mare says.
click image to zoomPhotos: Gary Vallad, University of FloridaBoth images involve research plots treated with (left to right) methyl bromide:chloropicrin 50:50 (350 pounds per treated acre); non-fumigated check; and PicChlor60 (300 pounds per treated acre). The photo on the left shows moderate nutsedge pressure; the photo on the right shows heavy nutsedge pressure. Regardless, Mbr 50:50 stands out the best in both.