Features Herbicides Seed & Chemical
Product-in-waiting

Nestled in a small research plot in the back fields of the University of Guelph's
Elora Research Station lies the answer to the weed woes of some Canadian potato
producers. That is what Dr. Clarence Swanton, a weed science professor and researcher
at the university, believes. As lead researcher of the trial, he is examining
the usefulness of a selection of herbicide chemistries for weed control in potato
production. And one herbicide is standing out: flumioxazin.

"I'm very pleased with it," says Swanton. "The neat thing about
this is you have a new chemistry that shows selectivity… and it's a new mode
of action."

Flumioxazin, which is marketed by Valent USA under the name Chateau, showed
'promising' control of weeds in potatoes when used pre-emergence during Swanton's
2006 trials. The chemistry was tested at a rate of 53 grams of active ingredient
(gai) per hectare and 106 grams of active ingredient per hectare. Both rates
showed good control but Swanton warns, "There is potential for burn. Research
also shows it doesn't affect tuber yield but it may have an effect when used
with other chemistries."

His findings are similar to those observed by weed research scientist Dr. Jerry
Ivany, based at Agriculture and Agri-Food Canada's Crops and Livestock Research
Centre in Charlottetown, Prince Edward Island. He first started working with
flumioxazin in 2003, testing it on Russet Burbank under a conventional potato
production system: plant, apply herbicide, cultivate and then hill. "Pre-emergence,
I'd love to have it," he says. "It has some utility."

Ivany tested the chemistry at a rate of 100 grams of active ingredient per
hectare at three production stages: pre-emergence (within seven days of planting),
at ground crack (17 to 20 days after planting and before potatoes emerge), and
post-emergence (when potato plants were four to six inches tall). The pre-emergence
application had "very good season-long control," he recalls. "We
did see a little bit of injury if any shoots had broken through," he says
about the ground crack application, adding that weather can also play a role
in plant damage, especially if it rains within a few days of the chemical application.
"Potatoes do come out of it," he says. "We saw about a five to
10 percent yield reduction when potato shoots were emerged at application and
rain occurred soon after application."

He disagrees with the use of flumioxazin for a post-emergence application.
"There's too much injury; too much yield reduction," he says, adding
his test results ranged from four to 33 percent plant injury. "Post-emergence
would not be advisable." Ivany says flumioxazin 'still has to be researched'
under the potato production system that a portion of growers use in Prince Edward
Island, which involves hilling between planting and potato emergence with no
other cultivation opportunity. He also has not examined the herbicide's effect
when used with short season varieties, such as Superior or Kennebec.

Swanton plans to continue the Elora based potato trial work. "I'd like
to go long-term, expand the trial," he says, adding the Ontario Potato
Board will be assisting with weed science research funding for the 2007 season.
"Without their support, minor use registrations won't go ahead in potatoes."

Both research scientists admit there has been very little work done involving
herbicide registrations for potatoes. "Just a little bit here, a little
bit there," says Ivany.

"It's been a long time since there's been any new herbicide technology
introduced in potatoes," says Swanton. "I don't think there's a lot
of work being done in that area. The potato industry needs to step up to the
plate." He adds that many of the older herbicide chemistries currently
used in Canadian potato production are under threat of losing their overall
effectiveness.

Ivany says Prince Edward Island growers are currently experiencing resistance
to metribuzin (Sencor) in lamb's quarters and Ontario growers are observing
the same resistance from red root pigweed. "They're starting to run into
resistance," he says. "They are recognizing the need for something
new." He adds that flumioxazin does give good control of lamb's quarters,
so it should fit well on Prince Edward Island, but is weak on wild radish, which
is a problem for some growers.

Flumioxazin is a n-phenylphthalimide or dicarboximide and works by inhibiting
the weed plant's production of a specific enzyme necessary for photosynthesis,
protoporphyrinogen oxidase. While inhibition of photosynthesis also plays strongly
in the weed control action of metribuzin (Sencor) and linuron, both important
herbicides in potato production, the area targetted during the process is unique
from that targetted by flumioxazin, thus providing a novel mode of action and
a new tool for resistance management.

"A different mode of action is very important in terms of overall resistance
management," explains Swanton, who is also testing flumioxazin for weed
control in onion and grape production. "We know the product works. We think
there's enough evidence to suggest it can be used in a production program. We're
doing everything we can to get the product introduced to the industry."

So too is Valent USA, which is handling the product for the North American
market. "We are full bore behind this," says Eric Tamichi, a project
manager with Valent USA. "We are taking this initiative very seriously."
He says the company, which currently markets products in Canada through Engage
Agro and Plant Products Company, plans to submit flumioxazin for Pest Management
Regulatory Agency (PMRA) approval by June 2007. It is hoped potatoes will be
on the list of crops, which will also include soybeans and ornamentals, seeking
label approval.

"We're working hard to make it happen," explains Tamichi, adding,
"It's come down to a timing issue. We don't want growers to have to wait
another two-and-a-half to three years for registration." If use in potato
production makes the flumioxazin label, it will hopefully be available before
2010. -30-