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.