The Environmental Protection Agency recently registered the fumigant Paladin from Arkema, adding another weapon to growers’ meager arsenal of soil-borne pest control.
Although the product, which contains the active ingredient dimethyl disulfide, is not a drop-in replacement for methyl bromide, researchers say it nonetheless has a fit.
“There’s no drop-in replacement for methyl bromide,” says Andrew MacRae, an assistant horticulture professor with the University of Florida’s Institute of Food and Agricultural Research in Wimauma. “There’s nothing that is going to be as good as methyl bromide is. The reason why is methyl bromide was forgiving.”
The fumigant, which is considered an ozone depleter and is being phased out, worked well even if fields were wetter or drier than optimal, MacRae says.
Husein Ajwa, a University of California Extension vegetable specialist based in Salinas, conducted initial trials with DMDS, and he says the fumigant has a place.
“It’s a good material if you have enough chloropicrin to help with fungal pathogens,” Ajwa says. “However, the material doesn’t provide as good of weed control as we get with some of the other fumigants, like bromide or iodemethane. But it could fill some of the gaps we have, such as with the limited supplies of Telone.”
State registration pending
The Environmental Protection Agency recently granted a Section 3 registration to Paladin after three years under an Experimental Use Permit. During that time, it was used in field trials and demonstrations in Florida, Georgia and North Carolina.
The product is federally registered on tomatoes, peppers, eggplants, cucumbers, melons, strawberries and ornamentals.
Clem McKown, Arkema North America’s director of business development for the thiochemicals business unit in Philadelphia, wouldn’t venture to guess when Florida will register the fumigant. But MacRae says he expects the Florida Department of Agriculture and Consumer Services will register it in October or November. If that proves true, then growers could begin using Paladin as early as December, he says.
Arkema named United Phosphorus Inc., or UPI, of King of Prussia, Pa., the exclusive distributor.
“UPI is going to play a very central role working with customers to control the odor and to inform the community and first responders and growers about how to use it safely and properly,” McKown says.
Agricultural chemical distributors will tankmix Paladin with chloropicrin at a 79:21 ratio by weight before selling it to growers.
Applicators will have to undergo mandatory stewardship training before they can use it, he says. The label also requires use of VIF plastic mulch as well as a number of other steps to reduce possible worker and bystander exposure issues.
Odor will be a challenge
One unique trait growers will have to manage is DMDS’ odor, which isn’t particularly dangerous but can be offensive, Ajwa says.
DMDS is derived from sulfur compounds, and it smells like strong garlic.
“We evolved to recognize reduced sulfur compounds as bad stuff or danger,” he says. “We can sense reduced sulfur compounds at parts per billion or parts per trillion. The material itself isn’t that dangerous, but we can actually smell it at very, very low concentrations.”
In fact, the Paladin label carries the signal word “warning,” compared with other fumigants that have the signal word, “danger.”
Using virtually impenetrable film or VIF mulch should help reduce some escaping odor.
If growers apply it through drip irrigation, Ajwa says he expects the water also will help control off-gassing.
Tony Jennison, farm production manager with West Coast Tomato Inc. in Palmetto, was one of the growers who participated in the EUP trials.
He describes the results as “good and not so good.” But he says he hasn’t ruled out trying Paladin again.
On the plus side, Jennison says he had no weed issues with Paladin, even in Manatee County, where weeds can be more troublesome.
Production-wise, he says he saw no difference between Paladin and his standard PicChlor 60.
On the down side, he says the workers complained about the smell.
“The odor from it was offensive to the labor,” Jennison says. Even four to five weeks after application, the workers still complained about the odor coming through the holes in the plastic punched for transplants.
West Coast is slowly converting its acreage over to drip-applied fumigants with a single drip line on 24-inch beds.
“Worker safety is just paramount to us,” Jennison says, adding that the drip application greatly reduces worker exposure to a fumigant.
He says he’s interested in possibly trying Paladin once Arkema obtains the drip label in Florida, because the water from the drip may help reduce the fumigant odor.
Paladin EC, the drip formulation, is registered federally. State registrations are pending.
Good nematode control
Ajwa conducted strawberry and cut flower field trials with DMDS early in its development, looking at different combinations with chloropicrin. Among the formulations were 50/50 DMDS and chloropicrin and 79/21 DMDS and chloropicrin.
“The issue here for strawberry growers are fungal pathogens, and DMDS doesn’t control fungal pathogens as well—it’s more toward nematodes,” Ajwa says. “For other crops that suffer from nematodes, I see it as standing up to the reputation of methyl bromide.”
A standard preplant treatment for California strawberry growers involves a combination of 66 percent Pic 60 EC and 33 percent Telone applied through drip irrigation.
Strong on nutsedge
In his four years of working with Paladin in combination with chloropicrin, MacRae says the 79:21 ratio was strong on nutsedge, nematodes and diseases.
Where he sees a weakness is with annual grasses, such as goosegrass. The fumigant also is weak on some broadleaf weeds, such as lambsquarter.
Depending on the crop, post-emergence herbicides such as Poast or Select Max can clean up annual grasses.
MacRae recommends that growers with broadleaf weed problems apply an herbicide on top of the finished bed and under the plastic to form a treated barrier.
“I see a really, really nice fit in peppers, since we can go in with Dual and Devrinol under plastic,” he says.
One of the challenges MacRae sees with Paladin, as well as some of the other new fumigants, is it doesn’t readily move through the soil when it’s too wet.
If a grower treats his field in the fall, he has no control over Mother Nature and subsequent storms. If it rains, he’ll have to wait longer than the typical timeframe for the soil to dry and for the fumigant to dissipate before planting.
“If you don’t extend the plant back, you’re going to increase injury to the crop,” MacRae says.