ield research was conducted in
2005 to compare early weed control with bromoxynil,
DCPA, dimethenamid-P and pendimethalin
(aqueous capsule formulation) in onion (Allium cepa L.) and to evaluate the injury caused by these
herbicides on onion.
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 7.9 pH, 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. Herbicides were applied at a low, medium
and high rate, starting with the middle labeled rate and increasing and
decreasing the middle rate by half. Treatments were applied immediately after
planting, except bromoxynil, which was applied 10
days after planting. Herbicides were applied with a CO2-pressurized
backpack sprayer delivering 20 gal/A 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 at 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 pendimethalin at a rate of 0.62 lb. ai/A at a volume of 20 gal/A was also made after the fifth-leaf
stage as a final late-season weed control measure. A final weed control
evaluation was made 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.
Dimethenamid-P applied at the high
rate reduced plant stand and plant height. Treatment eight
reduced height at four weeks after treatment, but at the end of the season
differences in height were not significant. At the end of the season
DCPA at the low rate and bromoxynil at all rate had
the highest weed density. However, all the plots were virtually weed free
throughout the growing season. There were significant differences among
treatments for cull, small and large grades and total yield. Pendimethalin and dimethenamid–P
at the middle and high rates resulted in yields similar to DCPA. Treatments 4,
6, 8 and 11 had the highest total yield with greater than 750 cwt/A. n
