The recently registered fumigant, Paladin, offers growers another option to help control soilborne pests.
Like nearly all soil fumigants, the product, which contains the active ingredient dimethyl disulfide, carries a host of Environmental Protection Agency requirements that must be met before and during application.
Among those are applicator stewardship training, a fumigant management plan and buffers.
But Paladin also has what the registrant, Arkema Inc., describes as a distinct garlic-like odor that continues to be an issue with some.
About two years ago, Stanley Culpepper, a University of Georgia weed scientist; Perry Fuller, manager of the TriEst Ag Group Inc., in Tifton, Ga.; and another colleague began exploring soil fumigant blends.
The goal was to reduce the overall amount of fumigant applied and the accompanying buffers yet maintain efficacy, Culpepper says. By reducing application rates, the three figured they should be able to reduce Paladin odor issues and improve economics.
The result was a blend of Paladin, 1,3-dichloropropene and chloropicrin nicknamed WSP. It is used in conjunction with high-barrier mulches, such as virtually impermeable film (VIF) or totally impermeable film (TIF).
“With WSP, you get the best of every world,” Culpepper says.
About 900 acres of WSP went out last year, mainly in Georgia, Fuller says.
“Overall, we’ve had good success with it in Georgia,” he says. “Most everyone repeated.”
Although Culpepper says they planned to tweak the ratio slightly this year to improve it, he said before the start of the season, “As of right now, I’m very excited about it. It’s very effective against nutsedge.
“We’re still trying to find out the best blend. We thought we had the best bend. But on 900 acres, we saw two or three hiccups.”
WSP also has to be used in conjunction with an herbicide program applied over the bed top since it’s weak on many other weeds.
As an agricultural chemical dealer in Georgia, TriEst is legally able to blend products together.
But Fuller says the firm is seeking to trade mark a formal name for the blend and obtain a full registration for it.
Background on Paladin
When tankmixed with the fumigant chloropicrin, Paladin has performed as well or better than a methyl bromide-chloropicrin blend in hundreds of field trials, says Andrew Horvath, global business manager for Arkema Inc., King of Prussia, Pa.
Nevertheless, he recommends that growers try the new fumigant on small acreage initially to learn how it will perform under their specific conditions.
“I’d like to have folks put it out on 5 acres,” Horvath says.
Because it’s weak on some weeds, Horvath says growers also may want to apply a pre-emergence herbicide, such as Devrinol, as a top dressing after bed preparation.
The Environmental Protection Agency registered DMDS in July 2010. Florida subsequently registered it in late 2011.
Paladin is available in two formulations: Paladin for shank application and Paladin EC for application through drip irrigation.
In multiple trials, a tankmix of Paladin with chloropicrin at a 79:21 ratio, accompanied by an over-the-bed herbicide program, produced results comparable to methyl bromide, Horvath says.
The Paladin label contains a list of approved TIF and VIF films that must be used in conjunction with the fumigant.
The newer films, which are required by EPA, hold fumigants in the soil longer, improving control of soilborne pathogens.
VIF and TIF films also minimize DMDS’ distinct garlic-like odor, Horvath says.
“If you treat it right and if you fumigate with best practices, there’s no problems,” he says. “The barrier films have been a tremendous help for us.”
Carl Grooms, a Plant City strawberry grower, has tried Paladin and says it performs as well or better than the standard 50:50 methyl bromide/pic blend and for a much lower cost.
Where Grooms says he has an issue is with Paladin’s mandatory buffers. Grooms lives on the edge of one of his fields, and the buffers prevented him from fumigating the part closest to his house.
But he says he realized the EPA imposed those same buffers on other registered soil fumigants on Dec. 1, 2012.
Grooms typically applies an herbicide barrier of Devrinol and Goal on the top of his beds and fumigates with either K-Pam or Pic-Chlor 60, a blend of chloropicrin and 1,3-dichloropropene.
Gary Vallad, a vegetable plant pathologist, is one year into a two-year field trial at the Gulf Coast Research and Education Center in Wimauma comparing different cultural techniques and herbicides to control yellow nutsedge.
Plots that were treated with the 79-21 Paladin/chloropicrin blend were clean, whereas nutsedge was poking through the plastic mulch in many of the other plots.
“The Paladin/pic does a great job on the nutsedge,” Vallad says. “It’s really important for pepper growers because there are very few herbicides labeled post-emerge.”
A long history with DMDS
Husain Ajwa, a University of California Cooperative Extension soil and water specialist based in Salinas, has conducted trials using the active ingredient in Paladin—DMDS—for several years.
During the past two years, he compared tankmixes of DMDS and chloropicrin with a 57:43 methyl bromide-chloride blend. All treatments were applied under a TIF plastic mulch in strawberries.
Altogether, Ajwa had 27 different treatments looking at different rates using deep-shank and drip application methods.
Some of the DMDS-pic rates were as good or better than those of methyl bromide-pic, he says.
Ajwa credited VIF and TIF for part of DMDS’ performance.
“In the old days, we tested DMDS under standard poly tarps, and we had variable results,” he says.
Ajwa says California growers are interested in Paladin because of restrictions placed on Telone.
“The growers are interested in it for one simple reason—we’re exceeding big time the township caps for Telone,” he says.
Ajwa was referring to township limits on the amount of Telone that can be applied imposed by the California Air Resources Board.
The Watsonville, Calif., area is heavily devoted to strawberries, a crop planted on ground typically fumigated annually. Until the caps were implemented, area growers relied heavily on Telone/chloropicrin blends as methyl bromide replacements.
The caps stem from an incident in the 1990s when air monitoring equipment in California’s Central Valley detected Telone at above-threshold levels.
As part of a program to bring the fumigant back into the California market, Dow AgroSciences, the product registrant, had to agree to use limits in each township.