REFERENCES

1
INTRODUCTION Interest in canola quality oilseed
rape, Brassica naupus L., in the southeastern US
has recently increased (Anonymous 2002) . There
are several potential markets for canola in this
region including 1) whole grain exports of
non-genetically modified canola, 2) newly
developed specialty oil lines, 3) improved
commodity prices (ERS-USDA 2002) and 4)
production uses for biodiesel. Agronomic
production of a profitable canola crop in the
southeastern U.S. will depend on reliable
information about rotational restrictions to
cotton, peanut, and other agronomic herbicides.
Agronomic row crop production in Georgia,
Florida, Alabama, and South Carolina represent
1,005,000 hectares of cotton, 323,300 hectares of
corn, 329,820 hectares of peanut, 348,030
hectares of soybean, and 25,500 hectares of
tobacco (NASS, 2002). Wheat, oats, and rye,
planted in winter rotations with these crops
represent 434,230 hectares (NASS, 2002). Canola
integrated as part of a winter rotation, October
planted and May harvested, could potentially
increase farmer profits, as an alternative oil
seed crop. Herbicides used in row crop production
in the southeastern U.S. vary by crop. In the
south, imazapic and diclosulam are applied to
approximately 85 of the peanut hectares.
Pyrithiobac is applied to greater than 30 of the
cotton crop. Imazapic, diclosulam, and
pyrithiobac mode of action is through
acetolactate synthase (ALS) inhibition. Other
ALS herbicides used in these crops include
chlorimuron and trifloxysulfuron. Herbicides
having different modes of action that are used in
the southeastern US in cotton and peanut include
sulfentrazone, fomesafen, and flumioxazin.
However, rotational data for these herbicides for
canola have not been established in the
southeastern U.S. One reason to evaluate canola
for herbicide carryover in this region is the
moderate temperature and moisture regimes that
can perpetuate the degradation of
pesticides. Clearfield canola cultivars have ALS
resistance, specifically to imidazolinone
herbicides. Clearfield-resistant canola was
marketed commercially in Canada during 1998 and
is now available for evaluation in the United
States. The use of Clearfield canola could be
very beneficial for canola growers in the
southeastern U.S., allowing the use of imazamox
herbicide that has selective control of wild
radish (Raphanus raphanistrum L.), many other
dicot weeds, and Italian ryegrass (Lolium
multiflorum Lam.) (Grey et al. 2003).
Additionally, Clearfield canola potentially could
be grown with reduced risk of injury, in rotation
with cotton, peanuts, and other row crops that
have had ALS mode of action herbicides (imazapic,
diclosulam, pyrithiobac, etc.) applied for weed
control. However, research for tolerance to
these herbicide has not been established. MATERIA
LS METHODS Experiments were conducted in
Georgia during 2002-2003 at the Bledsoe Research
Farm near Williamson and in 2003-2004 and
2004-2005 at the Southwest Georgia Branch
Experiment Station located near Plains in
separate areas of the same field. Soils were a
Cecil sandy clay loam (clayey, kaolinitic,
thermic, Typic Hapludult) at Williamson and a
Faceville sandy loam (clayey, kaolinitic,
thermic, Typic Kandiudults) at Plains. Organic
matter ranged from 1.0 to 2.0 with pH from 6.0
to 6.5 at both locations. In the fall of each
season, seedbeds were conventionally tilled using
a moldboard plow and smoothing with a rotary
tiller. Canola was seeded with a Great Plains
drill with a 19 cm row width on October 11, 2002,
November 11, 2003, and October 18, 2004 at a rate
of 28 seed per m of row. Each experiment was
arranged as a split plot with treatments
replicated four times. Plot size was 3.66 m wide
by 7.6 m long (Figure 1). Herbicides were PRE
applied with a CO2-pressurized backpack sprayer
calibrated to deliver 187 L/ha at 210 kPa.
Emergence dates for all trials was approximately
one week after planting. Split plots were seeded
on 1.83 m bed with imidazolinone-tolerant
Pioneer 45A71 and on the other 1.83 m bed to
the to conventional canola Flint. The intent
was to determine tolerance to ALS
herbicides. Screening of herbicide tolerance to
two classes of herbicides was investigated.
Modes of action included acetolactate synthase
inhibitors (ALS) and protoporphyrinogen oxidase
inhibitors (PPO). Five ALS herbicides and three
PPO herbicides were evaluated. Factors included
cultivars (IMI-tolerant canola and traditional
canola) and herbicide rate (1x, ½x, ¼x) that
resulted in 25 treatments. Treatments included a
nontreated check, the ALS herbicides diclosulam,
imazapic, chloriuron, pyrithiobac and
trifloxysulfuron, and the PPO herbicides
flumioxazin, fomesafen, and sulfentrazone.
(Table 1). Crop injury was visually estimated on
a scale of 0 (no injury) to 100 (death). Crop
injury ratings were taken at 140, 70, and 58 days
after planting (DAP) for the 2002, 2003, and 2004
plantings, respectively. Canola stand counts
were taken 58 DAP for the 2004 planting. Plots
were harvested (2004 only) with conventional plot
combine.
RESULTS AND DISCUSSION Pioneer 45A71 and Flint
canola exhibited extensive injury and nearly
complete stand failure (Table 1) and crop loss
with the PPO herbicides flumioxazin, fomesafen,
and sulfentrazone (Figure 4). This susceptibility
resulted in in no or significantly reduced yields
(data not shown). For the ALS herbicides
imazapic, chlorimuron, pyrithiobac, and
trifloxysulfuron, Pioneer 45A71 canola injury was
17 or less for all rates (Figure 5) and yields
were not different from the nontreated control
(Data not shown). Pioneer 45A71 exhibited
excellent tolerance to imazapic at ¼, ½, and 1x
rates (Figure 2). In contrast, Flint canola
exhibited 57 injury or greater (Figures 3 5)
and yield reductions for imazapic, chlorimuron,
pyrithiobac, diclosulam, and trifloxysulfuron at
all rates (Data not shown). Pioneer 45A71
exhibited dose response injury of 21, 43, and 63
for the ¼, ½, and 1x rates of diclosulam,
respectively (Figure 5). Additionally, stand was
reduced from 26 to 14 plants/m row for the
nontreated check to diclosulam at 82 g/ha,
respectively. This indicates that imi-resistant
canola is not resistant to all ALS herbicides
which should be considered when planning
potential rotational options for canola.
Figure 4. PPO inhibitor injury on Pioneer 45A71
and Flint canola.
Herbicide rate
injury
Herbicide/canola combination
Imazapic rate
Figure 2 (Left). Imazapic carryover simulation to
Pioneer 45A71 (left bed of each picture) and
Flint (right bed of each picture) at ¼ x (top), ½
x (middle), and 1x rates (bottom). Note dose
response for Flint from ¼x to ½x rates but no
difference for Pioneer 45A71.
¼ X
Figure 5. ALS inhibitor injury on Pioneer 45A71
and Flint canola.
REFERENCES Anonymous. 2002. Oilseed plant going
to Claxton in Georgia Faces. Univ. Georgia
College of Agric. Env. Sci. at
http//georgiafaces.caes.uga.edu Economic
Research Service - U.S. Department of Agriculture
(ERS-USDA). 2002. Title I, Commodity Programs in
Farm Policy, the 2002 farm bill provisions and
economic implications. at http//www.ers.usda.gov/
Features/farmbill/ National Agricultural
Statistics Service (NASS). 2002. National
Agricultural Statistics Service U.S. Dept. of
Agri.. 2000 Annual summary. NASS-USDA,
Washington, DC. Figure 1. Pioneer 45A71 (staked
bed, left) and Flint (nonstaked bed, right)
canola planted in Plains, GA.
injury
Herbicide rate
½ X
Figure 3 (Top). Imazapic carryover simulation to
Flint canola from ¼x application rate.
Herbicide/canola combination
1 X