Weed Control and Regulation

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Weed Control and Regulation

• Eric Johnson
• Agriculture and Agri-Food Canada, Scott Research
  Farm

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Sulfentrazone PPO inhibitor / Group 14
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Outline

• Authority herbicide
• Authority (sulfentrazone) has received
  conditional registration in chickpea
• Review of conditional registration
• Review Sulfentrazone tolerance and efficacy in
  flax
• Prospects for sulfentrazone registration in flax.

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Authority (Sulfentrazone) Registration

• Conditional registration for two years until
  additional data is conducted and reviewed
• Registration is for chickpea in Saskatchewan only
• Additional efficacy and re-cropping data required
  from PMRA to grant full registration
• Label is very restrictive.

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Authority Herbicide

• Use parameters
• Apply prior to planting or up to 3 days after
  planting.
• Application near or after crop emergence may
  cause severe injury.
• DO NOT APPLY TO FIELDS PREVIOUSLY TREATED WITH
  AUTHORITY IN THE PAST THREE YEARS (36 MONTHS).
• Performance parameters
• This product needs adequate moisture to activate.

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Authority herbicide

• Weeds controlled
• Authority will only control germinating weeds.
  Weeds that are present at application may not be
  controlled.
• Kochia
• Lambs quarters
• Redroot pigweed
• Wild buckwheat

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Sulfentrazone Application Rates and Restrictions

• Use on medium or fine textured soils only. NOT
  FOR USE ON COARSE (Sand, Loamy Sand) TEXTURED
  SOILS.
• Do not use on soils with a pH of 7.8 or greater.
• Do NOT apply to fine textured soils with less
  than 1.5 organic matter or any soil type with
  more than 6 organic matter.

Soil pH Soil pH
lt 7.0 gt 7.0
ml/acre (g ai ha-1) 118 (140) 89 (105)
Acres/jug 32 43
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Authority Re-cropping Label
Rotational Crop Replant Interval (Months)
Alfalfa 12
Canola 24
Sunflowers Anytime
Wheat, Spring 12
Wheat, Winter 16

• For crops not listed in the table (ie lentils), a
  minimum rotational crop interval of 36 months
  must be observed.

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Continuing Research on Sulfentrazone

• Efficacy lowest effective dose
• Re-cropping underway at 4 locations in Prairies
• Bioassay / sulfentrazone dissipation / impact of
  soil factors on sulfentrazone activity /
  sulfentrazone leaching led by Schoenau, U of S

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Flax Tolerance to Sulfentrazone

• Is dependent on soil cationic exchange capacity
  (texture, organic matter) and pH
• Cation exchange capacity more important than pH
• More injury in soils with low CEC low organic
  matter, coarse textured soils.
• Moisture is also important. High rainfall after
  application will increase potential for injury.

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Tolerance of Flax to Sulfentrazone. Scott, 2004.
a
a
a
a
a
Injury rating 2nd rating about 21 DAT Yield
expressed as a Percent of Hand-weed check
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Tolerance of Flax to Sulfentrazone. Scott, 2005.
a
a
ab
b
a
Injury rating 3rd rating near Crop
Maturity Yield expressed as a Percent of
Hand-weed check
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Tolerance of Flax to Sulfentrazone. Indian Head,
2005.
a
a
a
a
a
No visual injury at crop maturity
Injury rating 2nd rating at July 15, 2005 Yield
expressed as a Percent of Hand-weed check
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Sulfentrazone dose-response curves in ten soils
as determined by shoot length inhibition of sugar
beet
Sand, Clay, OC , pH
51, 31, 1.3, 7.8
k
19, 52, 1.3, 7.5
33, 39, 3.2, 5.6
23, 46, 2.3, 6.2
d
3, 83, 4.3, 7.2
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Sulfentrazone dose-response curves in ten soils
as determined by shoot length inhibition of sugar
beet
Sand, Clay, OC , pH
46, 38, 1.7, 7.7
k
14, 67, 3.0, 7.5
24, 51, 2.6, 6.3
d
60, 26, 2.4, 6.7
9, 72, 6.6, 6.1
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Relationship between I50 values for sulfentrazone
and percent organic carbon in ten soils as
determined by shoot length inhibition of sugar
beet under laboratory conditions.
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Relationship between I50 values for sulfentrazone
and percent clay content in ten soils as
determined by shoot length inhibition of sugar
beet under laboratory conditions.
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Conclusions Soil Properties

• The sugar beet shoot length bioassay is a
  suitable means of assessment for sulfentrazone in
  soil.
• Bioassay is simple and quick and can be easily
  replicated.
• Soil organic matter and clay content are
  important properties in reducing phytotoxicity
  from added sulfentrazone.

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Flax Tolerance Studies Funded by Sask. Flax

• Tolerance studies conducted at Lethbridge, AB,
  Scott, SK, Melfort, SK, Saskatoon, SK (2 soil
  types), Indian Head, SK, and Brandon, MB in 2006
  and 2007.
• Rates evaluated ranged from 35 to 560 g ai/ha

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Tolerance Results

• Lethbridge
• sandy clay loam (36 sand, 30 silt, and 34
  clay), 3.6 organic matter, pH 7.8.
• 2006 No injury observed
• 2007 highest rate (560 g ai/ha) resulted in
  unacceptable visual injury but did not affect
  plant stand or yield.
• Scott
• loam (38 sand, 41 silt, and 21 clay), 3.5
  organic matter, pH 6.5.
• 2006 and 2007 Unacceptable injury at rates of
  560 g ai/ha reduced plant stand and yield

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Tolerance

• Saskatoon (Silty clay loam soil)
• fine sandy loam (37 sand, 40 silt, and 23
  clay), 1.9 organic matter, pH 7.0
• 2006 Acceptable tolerance at all rates
• 2007 Slight injury and plant stand reduction at
  highest rates.
• Saskatoon (clay soil)
• 12 sand, 28 silt, and 60 clay), 4.5 organic
  matter, pH 7.2.
• 2006 Some injury at highest rate, but no
  reduction in plant stand or yield
• 2007 280 and 560 g ai/ha resulted in just
  acceptable and unacceptable ratings at first
  rating date however, crop recovered and no
  injury was evident at last rating date. Highest
  rate resulted in a reduced plant stand but yield
  was not affected.

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Tolerance

• Melfort
• Silty Clay loam (16 sand, 40 silt, and 44
  clay), 11.3 organic matter, pH 6.6.
• 2006 Injury observed at highest rate but no
  yield reduction
• 2007 No injury.
• Indian Head
• Clay (16 sand, 20 silt, and 64 clay), 4
  organic matter, pH 7.5.
• 2006 no visual injury or reduction in plant
  stand
• 2007 no visual injury some reduction in plant
  stand at highest rate no yield reduction.
• Brandon
• Clay loam (31 sand, 35 silt 34 clay ) 6.8
  organic matter, pH 7.7
• 2007 Unacceptable crop injury at first rating
  date at rates of 140 g/ha but crop recovered
  and no injury recorded at 2nd and 3rd rating
  dates. No plant stand or yield reduction.
• 2006 Unacceptable crop injury at highest rate
  early in the season but crop recovered and no
  yield reduction.

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Weed Control Results
Rate (g ai/ha) required to obtain 80 control of

• NP not present
• site evaluated or weed present for only one
  year
• (1) (2) results in first year vs second year

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Weed Control Results Additional Observations

• Round leaved mallow
• Present in Lethbridge in one year only
• Not controlled at any rate
• Shepherds purse
• Present at 2 sites Scott (2006) and Elstow (2007)
• At Scott 2006 - gt80 control at rates of 140 at
  Elstow (2007) not controlled at any rate.

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Weed Control Results Additional Observations

• Wild mustard
• Present at Kernen (2007).
• Not controlled at any rate.
• Russian thistle
• Present at Goodale (2006)
• Controlled at 70 g ai/ha.

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General conclusions from Flax Studies

• A rate of 140 g ai/ha appears to be safe on soils
  tested, including a 2X rate margin of safety.
• On most soils, rates of 140 g ai/ha or less were
  adequate to control redroot pigweed, wild
  buckwheat, and kochia. This is a rate that is
  safe to flax even at a 2 times that rate
  (overlaps).
• On high organic matter soils, concern over lack
  of control of redroot pigweed.

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Effect of herbicide systems on control of wild
mustard, kochia, and cleavers in flax. Scott
2008.
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Issues with Sulfentrazone registration

• Re-cropping issues PMRA wants more re-cropping
  information.
• More efficacy data required
• Concerns over its solubility / potential to
  leach.
• Wont be any further registrations for
  sulfentrazone until PMRA is satisfied that data
  requirements are met.

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Lentil Injury from Sulfentrazone Residue - Scott

• Sulfentrazone injury in lentil

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Projects Underway / Future

• Bioassay being used to measure dissipation and
  determine sulfentrazone ½-life in a number of
  prairie soils.
• Bioassay being used to measure sulfentrazone
  movement in soil profile.
• Some field work underway to ground-truth
  predictive ability of bioassay.
• 2 years of re-cropping studies being conducted at
  a number of locations (including Scott).
• More efficacy trials being conducted (including
  Scott).
• Lentil cultivar tolerance to sulfentrazone
  (CDC).

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ACKNOWLEDGEMENTS SASKFLAX PESTICIDE RISK
REDUCTION PROGRAM SASKATCHEWAN PROVINCIAL MINOR
USE PROGRAM
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