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Broadleaf weed control in chickpeas shows potential

Research on two herbicides may eventually lead to registration.


November 20, 2007
By Bruce Barker

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Broadleaf weed control in chickpea crops can be summed up by one herbicide,
Sencor. However, on-going herbicide research at Agriculture and Agri-Food Canada
(AAFC) may eventually lead to one or two new herbicide options in chickpea.

Eric Johnson, research scientist with AAFC at Scott, Saskatchewan says that
earlier work at AAFC Scott and at the University of Saskatchewan by Ken Sapsford
and Rick Holm screened a number of North American herbicides and narrowed down
the choices to two potential candidates. "The research is on-going, but
an application for sulfentrazone has been made to PMRA under the User Requested
Minor Use Registration program," explains Johnson.

Sulfentrazone is not registered in Canada for any crop at this time. It is
registered in the US as a pre-plant, soil applied herbicide for control of many
broadleaf weeds in soybean, sunflower and tobacco. It has also received emergency
registration in North Dakota to control wild buckwheat in chickpeas and dry
field peas. Sulfentrazone is marketed in the US by FMC.

Sulfentrazone requires moisture to activate and move it into the soil. The
US label states that one-half to one inch of rainfall within seven to 10 days
after application is required for best results. Incorporation may improve the
weed control efficacy of sulfentrazone, but the majority of the research has
focussed on using the herbicide in a zero-till situation. There is no indication
that crop residues tie up the herbicide; the primary concern is for rainfall
to move the herbicide into the rooting zone.

Sapsford says that fall applications may work better in Saskatchewan as the
snowmelt could move the product into the soil and activate the active ingredient.
Under the moister conditions experienced in 2004 and 2005, spring applications
were as effective as fall applications.

Research in western Canada has shown sulfentrazone controls wild buckwheat,
kochia, lamb's quarters and redroot pigweed, along with suppression of wild
mustard.

Figure 1. Yield response in chickpeas from isoxaflutole
(IFT) treatment. Means of four site years of data. Saskatchewan and Alberta,
2002 to 2004.
 6b

Chickpea tolerance to sulfentrazone is very good. Field pea tolerance is fair,
dry bean tolerance is poor and lentil is extremely sensitive.

Sapsford says there are some recropping concerns with sulfentrazone. Cereal
crops appear to be tolerant to the residues the following year, but canola is
listed as having a 24 month interval from application to planting on the US
label.

At Scott, Johnson found lentil injury to sulfentrazone residues three years
after application. "One of the concerns is that we feel the rates we have
been using are too high. We are going to focus more research on lower rates,
which may have an impact on the recropping situation," he says.

Currently, FMC has applied for registration of sulfentrazone in Canada on sunflower.
If that is granted, then the minor use on chickpeas would be considered.

The other herbicide showing potential is isoxaflutole. As a pre-plant, soil-applied
herbicide, this product also requires rainfall to activate and move it into
the soil. Isoxaflutole is a pro-herbicide meaning that it has to be converted
to an active form to effectively control weeds. In the soil, isoxaflutole is
converted to its active form through hydrolysis, therefore water is required
for this chemical reaction to occur. Incorporation would not likely improve
control since it could dry the soil and reduce the likelihood of hydrolysis
occurring. So far, there has not been any problem identified with heavy crop
residues tying up the herbicide.

When activated by rainfall, isoxaflutole controls wild mustard, common lamb's
quarters, kochia, red root pigweed, shepherd's purse, wild tomato and suppresses
green foxtail. However, it does not control wild buckwheat or cow cockle.

Johnson says that tolerance of chickpeas to isoxaflutole has been good, although
some crop injury occurred at higher rates. Field peas, lentil and dry bean do
not tolerate isoxaflutole.

At this time there are also some soil residue concerns with isoxaflutole. Preliminary
research at Scott indicates that cereal crops can be grown the year after application.
Further trials need to be conducted to look at other crops seeded two years
after application, as lentil crops are very susceptible to injury from this
herbicide.

"We are really still at the development stage with isoxaflutole. The company
has some recropping concerns as well," says Johnson.

Unique chemistries will bring benefits
Isoxaflutole is a Group 27 herbicide and sulfentrazone is a Group 14 herbicide.
Neither group is currently used in western Canada and Johnson says that their
introduction would be of benefit in controlling herbicide resistant weeds, such
as Group 2 resistant kochia. "That's another reason we would like to see
the herbicides registered here," says Johnson.

While isoxaflutole appears to have limited crop options, likely corn, buckwheat
and chickpeas, Johnson says that sulfentrazone may have a broader impact. He
explains that sulfentrazone shows potential for use on sunflower, chickpea,
flax, field pea, fababeans and lupins. "We're hoping that the technology
would be of use on those other crops as well, which would be good news for farmers
trying to control Group 2 resistant kochia."

Figure 2. Effect of sulfentrazone rate on injury
and yield of pulse crops. Industry standard is Sencor for chickpeas and
lentils, Odyssey for field peas and Basagran for pinto beans. n = number
of site years of data collection from 2004.
 6d

In addition to sorting out herbicide rates and recropping intervals, Johnson
is looking at reduced rates of sulfentrazone and isoxaflutole in a tank-mix
application. Isoxaflutole is good on mustards and cruciferous weeds but weak
on wild buckwheat. Sulfentrazone, on the other hand, is strong on wild buckwheat
and both herbicides are strong on kochia. "We are hoping that the reduced
rates might reduce the recropping restrictions."

The research, with funding from the Saskatchewan Minor Use Program and AAFC's
Pesticide Risk Reduction Initiative, is making slow progress towards expanding
the herbicide options in chickpeas. Johnson says more research is required across
a broader range of sites, especially for the recropping trials, but with limited
resources and funding, the work takes longer. "We're close but not quite
there with sulfentrazone," he says. -30-