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WEED CONTROL IN ONION WITH POSTEMERGENCE HERBICIDES††
Corey
V. Ransom,
Charles A. Rice, and Joey K. Ishida
Malheur
Experiment
Station
Oregon
State
University
Ontario,
OR, 2004
Introduction
Weed
control is essential for the production of marketable onions. Weed control in onions is difficult compared
to many crops because of the lack of a complete crop canopy and limited
herbicide options. Chateau®
(flumioxazin),
formerly called Valor®,
and Nortron®
(ethofumesate) are
two experimental herbicides that have been evaluated for use in onions
in past
research trials. Trials were conducted
this year to determine the benefits of using these experimental
herbicides in
postemergence herbicide combinations and compare their performance to
registered herbicide combinations.
Methods
General
Procedures
Trials
were conducted at the Malheur Experiment Station to evaluate
experimental and
registered herbicides for weed control and onion tolerance. Trials were conducted under furrow
irrigation. On March 25, onions (cv.
'Vaquero', Nunhems, Parma, ID) were planted at 3.7-inch spacing in
double rows
on 22-inch beds. Plots were 4 rows wide
and 27 ft long and arranged in a randomized complete block design with
four
replications. Lorsban®
was applied in a
6-inch band over each double row at 3.7 oz/1,000 ft of row. Onions were sidedressed with 175 lb nitrogen
(N), 30 lb phosphorus (P), 35 lb sulfate, 38 lb sulfur (S), 2 lb Zinc
(Zn), 3
lb manganese (Mn), and 1 lb boron (B)/acre on June 3.
Registered insecticides and fungicides were applied for thrips
and downy mildew control.
Herbicide
treatments were applied with a CO2-pressurized backpack
sprayer. Preemergence applications and
postemergence grass herbicides were applied at 20 gal/acre at 30 psi
and
postemergence treatments were applied at 40 gal/acre at 30 psi. All plots were treated with a preemergence
application of Roundup®
(glyphosate) at 0.75
lb ai/acre plus Prow®l
(pendimethalin) at
1.0 lb ai/acre on April 5 and a postemergence application of Poast®
(sethoxydim) at 0.19
lb ai/acre plus crop oil concentrate (COC) (1.0% v/v) on June 16. Postemergence treatments were applied to
two-leaf
onions on May 6, two- to three-leaf onions on May 14, and to five-leaf
onions
on June 2. In the Chateau application
timing trial, a separate application of Chateau was made to three-leaf
onions
on May 18. Weed control and onion
injury were evaluated throughout the season.
Onions were harvested September 16 and 17 and graded by size on
October
1-4.
Data
were analyzed using analysis of variance and means were separated using
a
protected least significant difference (LSD) at the 5 percent level
(0.05).
Comparison
of Postemergence Chateau or Goal Combinations
Chateau
and Goal®
(oxyflurofen) were applied in combinations with Buctril®
(bromoxynil) to
evaluate weed control and onion tolerance.
Buctril, Goal, and Chateau were evaluated at two rates. Comparisons of Goal or Chateau with Buctril
included several combinations of herbicides and rates.
Additional treatments included a split
application of Chateau applied to two-leaf and again to three-leaf
onions, and
a comparison of Buctril plus Chateau treatments following preemergence
applications of Roundup, Prowl, and Dacthal®
(DCPA).
Application
Timings for Chateau
Chateau
was applied at two rates in combination with Buctril to two-leaf or
three-leaf
onions. Chateau treatments were
compared to Goal plus Buctril. Additional
treatments included Chateau in a separate application 4 days after the
Buctril application
at the three-leaf application timing.
Addition
of Nortron to Postemergence Treatments
This
trial was conducted to determine if the addition of Nortron to
postemergence
herbicide applications would improve weed control.
Each treatment was applied with or without Nortron added to the
two-leaf
and three-leaf applications at either 0.25 or 0.5 lb ai/acre. One treatment evaluated Outlook®
(dimethenamid-P) added
to the two-leaf application and Nortron added to the three-leaf
application.
Results and Discussion
Preemergence
herbicides worked fairly well due to rainfall in April.
Adequate rainfall also ensured that weeds
were actively growing when postemergence treatments were applied.
Comparison
of Postemergence Chateau or Goal Combinations
Because
the preemergence application of Prowl was so effective, there were no
differences in weed control between any of the postemergence herbicide
treatments (Table 1). Control of all
species was 85 percent or greater.
There were also no differences in onion injury among treatments.
This is surprising as there were large
differences in the herbicide rates applied for different treatments. There were a few differences in onion yields,
with higher yields resulting from treatments with additional
soil-active
herbicides applied or with higher rates (Table 2).
Application
Timings for Chateau
Treatment
with Chateau combined with Buctril when applied either to two-leaf or
three-leaf
onions did not cause greater injury than combinations of Goal plus
Buctril
(Table 3). When Chateau was applied alone
4 days after Buctril was applied to three-leaf onions, injury increased
significantly. By July 21 there were no
differences in onion injury among treatments.
The injury caused by the delayed application of Chateau was
probably
related to wet cool weather that occurred after the Buctril application
and
prior to the Chateau application.
Pigweed (redroot pigweed and Powell amaranth), common
lambsquarters,
hairy nightshade, and barnyardgrass control was not different among
herbicide
treatments and was 88 percent control or greater. Kochia
control was significantly greater with treatments that
contained Chateau tank-mixed with Buctril and applied at either the
two-leaf or
three-leaf timing compared to Buctril plus Goal. Treatments
where Chateau was applied alone following the Buctril
application to three-leaf onions did not control weeds better than
Buctril plus
Goal.
There
were few significant differences in onion yields between herbicide
treatments,
with marketable yields ranging from 1,107 to 1,459 cwt/acre.
Addition
of Nortron to Postemergence Treatments
Onion
injury was not different among treatments on either evaluation date
(Table
5). Pigweed, hairy nightshade, and
barnyardgrass control was similar among herbicide treatments and was 89
percent
or higher. The addition of Nortron at
either rate to Buctril significantly increased common lambsquarters
control,
but control was similar to that provided by Goal plus Buctril. There was no improvement in common
lambsquarters control when Nortron was added to Buctril plus Goal. Kochia control was less when Buctril was
applied alone compared to treatments containing Buctril plus Nortron or
Goal or
both. A few of the treatments
containing Nortron produced more supercolossal onions than did Buctril
alone,
but yields were similar to the other herbicide treatments (Table 6). Nortron is useful for improving weed control
in onion but in this trial did not provide greater benefits than the
currently
registered herbicides.
Table
1. Onion injury and weed control from Goal®
or Chateau®
combinations with
Buctril®,
Malheur Experiment Station, Oregon State University,
Ontario, OR, 2004.
|
|
|
|
Injury |
Weed
control† |
|||||||
|
Treatment |
Rate |
Timing* |
5-24 |
6-9 |
Pigweed |
Common lambsquarters |
Hairy nightshade |
Kochia |
Barnyard-grass |
||
|
|
lb
ai/acre |
Leaf |
----------------------------------------------------------------------------%------------------------------------------------------------------------- |
||||||||
|
Untreated |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
||
|
Roundup + Prowl Buctril Buctril + Goal Goal |
0.75 + 1.0 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
24 |
28 |
86 |
90 |
96 |
95 |
100 |
||
|
Roundup + Prowl Buctril Buctril + Goal Goal |
0.75 + 1.0 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
24 |
20 |
88 |
85 |
97 |
95 |
98 |
||
|
Roundup + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 1.0 0.125 + 0.063 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
25 |
18 |
96 |
95 |
96 |
100 |
100 |
||
|
Roundup + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 1.0 0.125 + 0.094 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
29 |
22 |
93 |
98 |
100 |
96 |
98 |
||
|
Roundup + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 1.0 0.25 + 0.063 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
21 |
16 |
93 |
98 |
96 |
100 |
99 |
||
|
Roundup + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 1.0 0.25 + 0.094 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
26 |
21 |
94 |
99 |
97 |
100 |
100 |
||
|
Roundup + Prowl Buctril + Goal Buctril + Goal Goal |
0.75 + 1.0 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
20 |
19 |
96 |
90 |
99 |
94 |
100 |
||
|
Roundup + Prowl Buctril + Goal Buctril + Goal Goal |
0.75 + 1.0 0.125 + 0.25 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
24 |
17 |
94 |
90 |
95 |
96 |
100 |
||
|
Roundup + Prowl Buctril + Goal Buctril + Goal Goal |
0.75 + 1.0 0.25 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
28 |
16 |
91 |
88 |
99 |
98 |
93 |
||
Table
1 (continued). Onion injury and weed control from Goal®
or Chateau®
combinations with
Buctril®,
Malheur Experiment Station, Oregon State University,
Ontario, OR, 2004.
|
|
|
|
Injury |
Weed
control† |
|||||||
|
Treatment |
Rate |
Timing* |
5-24 |
6-9 |
Pigweed‡ |
Common lambsquarters |
Hairy nightshade |
Kochia |
Barnyard-grass |
||
|
|
lb
ai/acre |
Leaf |
----------------------------------------------------------------------------%------------------------------------------------------------------------- |
||||||||
|
Roundup + Prowl Buctril + Goal Buctril + Goal Goal |
0.75 + 1.0 0.25 + 0.25 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
28 |
19 |
90 |
93 |
94 |
100 |
95 |
||
|
Roundup + Prowl Buctril + Chateau Buctril + Chateau Goal |
0.75 + 1.0 0.125 + 0.047 0.25 + 0.047 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
25 |
18 |
95 |
97 |
97 |
88 |
100 |
||
|
Roundup + Dacthal + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 7.5 + 0.6 0.25 + 0.094 0.125 + 0.25 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
27 |
21 |
97 |
92 |
100 |
96 |
100 |
||
|
Roundup + Dacthal + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 7.5 + 0.6 0.125 + 0.094 0.125 + 0.25 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
27 |
18 |
96 |
98 |
100 |
100 |
100 |
||
|
Roundup + Dacthal + Prowl Buctril + Chateau Buctril + Goal Goal |
0.75 + 7.5 + 0.6 0.25 + 0.094 0.125 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
24 |
20 |
96 |
100 |
98 |
100 |
95 |
||
|
LSD (P = 0.05) |
-- |
-- |
NS |
NS |
NS |
NS |
NS |
NS |
NS |
||
*Preemergence (PRE)
treatments were applied on April 5,
two-leaf (2-leaf) on May 6,
three-leaf (3-leaf) on May 14, and five-leaf (5-leaf) on June 2.
†Weed-control
ratings
were taken September 2.
‡Pigweed
is a
combination of redroot pigweed and Powell amaranth.
Table 2. Onion yield in response to Goal® or Chateau