Weed Control Systems for Winter Canola in the Southern Great Plains. Deena L. Morley, Mark C. Boyles

1
Weed Control Systems for Winter Canola in the
Southern Great Plains.Deena L. Morley, Mark C.
Boyles, and Thomas F. Peeper, Oklahoma State
University
Introduction Over the last decade the acreage of
winter wheat harvested for grain has declined in
Oklahoma. This is attributed to heavy
infestations of jointed goatgrass, Italian
ryegrass, and feral rye. Although there are
herbicides available for controlling these weeds
in winter wheat, in many cases more than one
herbicide is needed to control the variety of
weeds present. In 2002, winter canola was
introduced into western Oklahoma as a rotational
crop with winter wheat to expand options for weed
control. Herbicides registered for annual grass
control in winter canola include trifluralin,
quizalofop, clethodim, and glyphosate.
Trifluralin, applied preplant incorporated, is
labeled to control Bromus spp. and Italian
ryegrass. One disadvantage of using trifluralin
is that wheat cant be planted if canola stand
fails. Quizalofop is labeled to control
volunteer wheat and feral rye. Sequential
applications up to 139 g ai/ha per season can be
applied beginning at emergence up to 60 days
prior to harvest. Clethodim can be applied
sequentially up to 280 g ai/ha per season from
emergence to prior to bolting to control
volunteer wheat and Italian ryegrass. Glyphosate
can be applied to Roundup Ready varieties at 434
to 630 g ae/ha with a maximum of 870 g ae/ha per
season to control a large variety of weeds.
Our objective was to evaluate control options
in conventional and Roundup Ready canola systems.
quizalofop at 62 g ai/ha included nonionic
surfactant at 0.25 v/v. Clethodim applied at 88
g ai/ha in the fall and all mid-Feb. treatments
were applied with crop oil concentrate at 1
v/v. Plants were drought stressed throughout the
winter and spring. Glyphosate was applied at 630
g ae/ha. Weed control was visually rated
approximately one month after herbicide
application.
Results and Conclusions Volunteer wheat and
feral rye were controlled by several treatments.
However, control appeared less effective with
trifluralin and clethodim (Table 1). Jointed
goatgrass control was fair to poor with all
treatments except clethodim and glyphosate.
Fall applications are recommended especially in
years where precipitation is limited (Figures 1
and 2). Canola stands were reduced in the
untreated check is due to early competition.
Fall application of glyphosate was beneficial,
but a sequential spring application often
controlled a few escapes and weeds that emerged
later in the growing season.
Table 1. Volunteer wheat, jointed goatgrass, and
feral rye control in DKW 13-86 and Wichita winter
canola in northcentral OK.
Materials and Methods In 2005-2006, four
experiments were established in northcentral
Oklahoma to compare 8 weed control strategies in
conventional and Roundup Ready varieties. The
weed control strategies compared in both
conventional and Roundup Ready varieties were
1.) Untreated check 2.) Trifluralin applied
preplant incorporated (PPI) 3.) Trifluralin
applied PPI fb quizalofop in the fall 4.)
Quizalofop applied in the fall 5.) Quizalofop
applied in the spring 6.) Quizalofop applied in
the fall fb quizalofop applied in the spring 7.)
Clethodim applied in the fall. In addition to
the seven previously mentioned strategies, the
Roundup Ready variety was treated with a single
fall application of glyphosate and sequential
applications of glyphosate in the fall and
spring. Prior to planting the canola, jointed
goatgrass at 134 kg/ha, volunteer wheat at 67
kg/ha, and/or feral rye at 17 kg/ha were evenly
distributed and lightly incorporated throughout
each plot. Winter canola varieties DKW 13-86
(Roundup Ready) and Wichita (conventional) were
planted September 29 7 days at a seeding rate
of 6 kg/ha. Trifluralin was applied at the 1X
rate just before planting and incorporated with
an s-tine field cultivator. Fall treatments were
applied approximately one month after planting
and spring applications were in mid-February.
Fall applications of
Figure 1. Feral rye control.
Untreated Check
Trifluralin fb quizalofop
Clethodim
Glyphosate (Fall)
Glyphosate (Fall fb Spring)
Figure 2. Volunteer wheat and jointed goatgrass
control
Untreated Check
Trifluralin fb quizalofop
Clethodim
Glyphosate (Fall)
Glyphosate (Fall fb Spring)