ield research was conducted in
2005 to determine the effect of bromoxynil and oxyfluorfen rate and spray volume on early postemergence
weed control in onion (Allium cepa L.). Bromoxynil and oxyfluorfen are
two postemergence herbicides commonly used in onion, but both may cause onion
leaf injury, so a high application volume (50 gal/A) is necessary to increase
crop safety. In addition, onion must be
in the two-leaf stage before herbicide application, but at this stage, many
broadleaf weeds are already too large for control by either herbicide.
The study was conducted at the Carrington
Research Extension
Center, Carrington, ND.
The soil was a Heimdal-Emerick/Fram-Wyard loam with
2.9% organic matter and a pH of 7.9, with soybean as the previous crop. Onion
variety ‘Teton’ pelleted seed was planted on May 3 using a Stanhay
four double-row planter unit, with 4-inch paired rows and 14 inches between
main rows. Bromoxynil
was applied at 0.075 and 0.3 lb. ai/A and oxyfluorfen at 0.025 and 0.1
lb. ai/A. High
and low herbicide rates were sprayed with 10, 25 and 50 gal/A of water.
Treatments were applied at the first-true-leaf stage (June 9) with a CO2-pressurized
backpack sprayer delivering the necessary volume to 6 foot wide and 20 foot
long plots arranged in a randomized complete block design with four
replications. Treatments were evaluated for weed coverage and control and onion
height and injury one and three weeks after application. At the fifth-leaf
stage, a standard application of 0.375 lb. ai/A bromoxynil and 0.125 lb. ai/A oxyfluorfen was made to all treatments, except checks, at a
volume of 50 gal/A. An application of 0.62 lb. ai/A pendimethalin at a volume of 20 gal/A was made after the
fifth-leaf stage as a final late-season weed control measure. A final weed
control evaluation was taken one week before harvest. On September 22, 10 feet
of the middle two rows of each plot were harvested for grade and yield
analysis. After harvest, onions were allowed to cure and then were graded.
Split, diseased and double bulbs were graded as culls, regardless of diameter.
Onion height early in the growing season was affected by
treatment. However, one week before
harvest, height was similar for all treatments except the weedy check. Plant
stand was not affected by treatment. Treatments at the low rate and 50gal/A spray volume had the greatest weed density for both
herbicides. Grades of cull, small and medium onions were not significantly
different among treatments. Treatment differences were observed for large grade
onions and total yield. No treatment yielded as well as the hand-weeded check.
Treatments with oxyfluorfen resulted in the same
yield, regardless of rate and volume. With bromoxynil,
the low rate at all spray volumes and high rate at 10
gal/A were similar in yield and tended to yield better than the high rate at
the medium and high volume. n
