Fighting nematodes
The fight against nematodes uses a multi-pronged approach with fumigants continuing to be the primary mode of action followed by nematicides, green manures, clean equipment and using certified seed.
While fumigation continues to be the best means to control nematodes, fumigants face mounting restrictions from the EPA and state environmental agencies. Because of this, chemical producers and growers have begun looking for different nematode management programs than fumigation.
Nematodes can be found in almost every ecosystem. Though many are beneficial and their abundance and diversity are evidence of microbial activity in productive soils, there is a group of nematodes that play parasitic and pathogenic roles among potato plants.
The total number of nematode species is estimated to be more than one million, with about 25,000 nematode species presently identified. These tube-like, underground microbes account for an estimated 80 percent of all animals on earth.
The four main nematodes that infect potatoes are root-knot, root-lesion, stubby-root and sting. Potato rot nematode and two varieties of potato cyst nematodes are a source of regional problems within the potato industry.
In some regions root-lesion nematodes may interact with the verticillium fungi and contribute to early die-off, also called verticillium wilt and the stubby-root nematode can be a vector for tobacco rattle virus.
When it comes to nematodes, you have to emphasize management, said Saad Hafez, a nematologist at the University of Idaho’s Parma Research and Extension Center, during the Washington-Oregon potato conference in Kennewick, Washington.
It’s not something you can eradicate or eliminate,” he said. “Fumigation works very well controlling nematodes.”
Hafez said that current fumigants in use to control nematodes and potato diseases include Telone II, Telone C-17 and C-35 1,3D, Vapam (metam sodium), Metam Potassium and Metam Ammonia.
“Metam sodium is not really a true fumigant but reacts like a fumigant. It’s a contact biocide,” said Hafez.
Telone C-17 is a combination of Telone II and another fumigant, chloropicrin, with a dual mode of action against nematodes and verticillium.
Phil Hamm, station director at Oregon State University’s Hermiston Agricultural Research and Extension Center (HAREC), is also a strong proponent for fumigants.
“It’s expensive to fumigate but it’s expensive not to fumigate,” Hamm told the Kennewick audience. “If you don’t fumigate, you’re either going to have a yield that doesn’t pay you the money it costs to grow the crop or you’re going to have nematode problems and you’re going to be rejected anyway.”
“Fumigation is all about delaying the onset of disease,” Hamm said.
Hamm said that Telone II fumes well underground and is a great nematicide that does a good job on the four main varieties of nematodes.
“Because it’s so good at fuming,” Hamm said, “we shank it down at 16 to 18 inches. We put those shanks far apart and it works so well. It fumes so well it gets through all the soil particles.”
Hamm said that metam sodium, or Vapam, works best in a chemigation application, adding that water seems to move it down through the soil profile very well.
“We know with metam sodium, we’re using that product to reduce verticillium, the major cause of early die, fusarium, pythium and maybe others. It might have an impact on black dot and rhizoctonia as well,” Hamm said.
Hamm advised growers that when using metam sodium, to apply enough water to drive the material to a depth of 12 inches and to make sure when hilling to use treated soil.
He said that Telone C-17 performs very well but it’s more expensive to use in a broadcast application. At HAREC they’ve explored using C-17 in banding applications during planting to lower the cost of using it in the entire field.
While fumigation remains the first defense against nematodes, other lines of defense include nematicides, green manures and crop rotation.
“I want to emphasize that we’ve been working on a lot of new chemistry,” said Hafez. “In the last 10 years a lot of chemical companies have shown interest in developing new nematicides.
For years the list of nematicides was a short one that included Vydate, Mocap, Nimitz and Admire but Hafez said that there have been promising results with new products.
With all the non-fumigant products he said that both the application method and the timing of application is very critical for the treatments to be successful.
Hafez said that Nimitz, a nematicide produced by Adama, is a good nematicide but it doesn’t move well in the soil and is best used in combinations with other products, not as a standalone treatment.
Recently introduced products have been discovered to have efficacy against nematodes.
Hafez said that Bayer CropScience’s insecticide Movento has been effective against nematodes.
He said that Movento works systemically. The first application should be at the plant’s roseate stage and followed 14 days later by a second application.
“You have to apply it when you have enough foliage for penetration and you have to apply it with a surfactant,” Hafez said.
“Movento is a very active nematicide, not a standalone treatment,” he said. “You have to do it in combination with Vapam, Vydate or Mocap.”
Hafez recommended using Absorb, a soil penetrant, to aid in water movement with nematicides.
“We found out that when we mix Absorb with Vapam, we get better results controlling nematodes,” he said.
DuPont has been promoting its V2 program, a combination of Vydate and Vertisan, as a nematode management program with the benefit of reduced use of metam sodium.
The first year of V2 field trials proved promising said Jeff Miller, president and CEO of Miller Research. However, during the second year of trials, in 2014, he and other researchers did not see the same level of performance.
“We just don’t know enough to recommend it,” Miller said. “We’re still in the research mode and not prepared to go out and recommend it as an answer or suitable replacement to metam sodium.”
There will be limited supplies of Vydate in 2015 due to an industrial accident on Nov. 15, 2014, at the DuPont chemical plant in La Porte, Texas.
Hafez said that planting non-host plants or green manures are both effective preventative strategies to reduce nematodes.
He said that a study on corn, beans and wheat showed that corn is a bad rotation crop because the nematode can survive in the corn roots.
Green manure crops Hafez has been testing include mustard, radish, beets, lentils, cabbage and onion.
“Basically, if you’re planting brassica, radish or mustard, you’re adding natural vapam to the soil,” Hafez said.
Hafez said that the best solution to stop the spread of nematodes is to clean your equipment before moving from a field, to not use wastewater and to use certified seed.
“You can spread nematodes, especially root-knot, very easy with infected seed,” he said.
“If you can leave the field fallow for one summer you can get 90 percent control of root-knot,” Hafez said.
