Nufarm is again applying for an emergency registration of its Intego Solo seed treatment for use on field peas in Canada.
The Group 22 fungicide includes ethaboxam, the only active ingredient rated for suppression of aphanomyces, a soil born pathogen that Boyd Bergstrom, Nufarm’s western Canadian manager, referred to as a kissing cousin of clubroot.
“The latest survey said the 65 percent of fields tested (in the Prairies) had (aphanomyces) in them,” he told the Farm Forum Event in Saskatoon.
“Last year was dry, so it wasn’t as much of a problem, whereas the year before it was killing yields by 30 to 50 percent.”
Read Also
Sask. ag group wants strychnine back
The Agricultural Producers Association of Saskatchewan has written to the federal government asking for emergency use of strychnine to control gophers
Intego is already registered for lentils, chickpeas, dry beans and soybeans in Canada, and was granted emergency use registration in 2015 for use on field peas.
Intego is rated for suppression of aphanomyces by Agriculture Canada.
Bergstrom said an Agriculture Canada aphanomyces study, which used a scale of 0 to 5 with 5 being a dead plant and 0 a healthy plant, found that the untreated check was rated a 4.
“Intego reduced the infection and visual symptoms down to a 2.2, so at the end of the day — from a marketing standpoint suppression isn’t a really good word to use — but on the scale it was basically the difference between having a crop and not having a crop.”
Bergstrom said the federal studies have found an increase of eight percent in plant emergence over six trials and an increase of plant root length of 10 percent over four Intego trials.
Aphanomyces affects plants at early stages, so seed treatments need to be used to attack the disease.
“Will it protect against a high rainfall event in July? No,” he said.
“But will it provide it that three to four week window where it gives you some protection early in the season? Yeah. That’s the most vulnerable stage when you need to protect the plant.”
Aphanomyces infections often begin when oospores, which can be found either in the soil or in infected plant debris, germinate after receiving a chemical signal from the roots of a new host plant.
Oospore can germinate by direct germination, in which the oospores produce hyphae that directly penetrate host cells at the plant root tips.
In indirect germination, the oospores produce sporangia that release zoospores, which then encyst on the host plant cells and germinate.
Oospores are not mobile — they need to be next to the root to infect the plant. However, the infection, when it does occur, can cause zoospores, which can move in soil moisture toward other plant roots.
More resting spores, or oospores, may be produced once the zoospores infect a plant with their hyphae. These oospores can survive in soil for more than 10 years.
“That’s the main problem with this disease: once you have it, it’s there,” Bergstrom said.
Aphanomyces root rot is a monocyclic disease, which means only one infection cycle per season. However, all of the oospores do not germinate at the same time, nor do all of the zoospores infect plants at the same time.
Intego’s mode of action is to inhibit cell division.
“Basically, what that means it that it prevents those penetration hydrates,” he said. “They might get into the plant, but once they get a taste of the Intego, they can’t continue through the plant and generate more oospores.”
Producers reduce the need for inoculants in future years by reducing the amount of oospores.
Intego doesn’t come with a colorant, which means it needs to be mixed with another seed treatment.
“We haven’t found a seed treatment it won’t mix with,” Bergstrom said. “It’s compatible with all inoculants we’ve tested with the major inoculants manufacturers.”
The use rate is 5.33 millilitres per bushel.
“It costs $4.23 per bushel, so for a lentil grower, it costs for an investment payback at 34 cent lentils, you need about .2 bu. to pay back your investment,” he said.
“Pea growers need about a bushel and a half at $8.50 bu. peas.”
Roots that have a grey water-soaked appearance are an early sign of an aphanomyces infection. However, the roots will eventually turn a caramel colour, which will follow them up to the surface. This is the first visible above-ground symptom.
It takes about 10 days from the initial infection before visible signs appear on the roots.
Aphanomyces can affect lentils, peas, chickpeas, fababeans, alfalfa and clover.
Isolates from the various aphanomyces species affect host crops differently, so rotating pulse crops can have short-term beneficial effects.
“Unfortunately, in the long term, these isolates are sexually compatible and they can transfer genes,” Bergstrom said.
“The genes that they can transfer can include the virulence genes.”
Producers can reduce the number of oospores in the soil by using longer crop rotations, especially with crops that are not susceptible to aphanomyces infections.
Bergstrom said anything that affects root development could increase the risk for aphanomyces, such as wet conditions, cool temperatures early in the season, short rotations, heavy textures soil, compaction and poor nutrition.
As with clubroot, the pathogen can travel between fields on equipment and boots, so cleaning equipment after leaving an aphanomyces-infested field is a wise practice.
Producers who think they have an aphanomyces infection can send a soil or plant sample to a lab for testing.
