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SOIL-ACTIVE HERBICIDE APPLICATIONS FOR WEED CONTROL IN ONION††
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.
Only a few herbicides are registered for preemergence
application
in onion. Effective preemergence
herbicides can control weeds as they germinate and reduce the size and
number
of weeds that are present when onions are large enough to tolerate
postemergence herbicide applications.
This research evaluated registered and experimental herbicides
for
preemergence weed control in onion.
Methods
General Procedures
A trial was conducted
at the Malheur Experiment Station 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 4
replicates. 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, 30 lb phosphorus, 35 lb sulfate, 38
lb
elemental sulfur, 2 lb zinc, 3 lb manganese, and 1 lb boron/acre on
June
3. Registered insecticides and fungicides
were applied for thrips and downy mildew control.
Preemergence (PRE)
applications of Prowl®
(pendimethalin), Nortron®
(ethofumesate), and Outlook®
(dimethenamid-P) in combination with Roundup (glyphosate)
were evaluated for weed control and onion tolerance.
Each product was evaluated at two rates. Combinations
of Prowl with Nortron or
Outlook were also evaluated. Prowl and Prowl H20®
(a new water-based formulation) were also applied to onions
at the flag leaf stage following Roundup applied PRE.
Prowl H20 was also combined with Outlook applied at
the flag leaf stage following a PRE application of Roundup. Preemergence treatments and other
applications of soil-active herbicides were compared to plots where
only Roundup
was applied preemergence.
Herbicide treatments were
applied with a CO2-pressurized
backpack sprayer. Preemergence
applications
were applied at 20 gal/acre at 30 psi. Postemergence
applications were applied at 40 gal/acre at 30 psi.
Preemergence treatments were applied on April 5,
two-leaf on May 6, three-leaf on
May 14, and five-leaf on June 2.
All plots received
Poast®
(sethoxydim) at 0.19 lbs ai/acre plus crop oil concentrate (COC) (1
qt/acre) on
June 16 to control grasses. 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).
Results
and Discussion
Preemergence
and postemergence treatments were effective
because of rain and actively growing weeds at the time herbicides were
applied. Injury was similar among
treatments except
for plots treated with a tank mixture of Buctril, Outlook, and Chateau,
which
had significantly more injury than all other treatments on May 24 and
at the
later evaluation on June 9 (Table 1).
Pigweed (redroot pigweed and Powell amaranth) control was
similar among
herbicide treatments and ranged from 84 to 99 percent.
Common lambsquarters control was improved
with preemergence applications of Prowl compared to plots treated only
with
Roundup PRE. Outlook and Nortron did
not significantly increase common lambsquarters control compared to
Roundup
alone. Hairy nightshade control was
greater than 90 percent and barnyardgrass greater than 96 percent for
all
herbicides. Kochia control was
significantly greater with PRE Prowl or Nortron compared to Outlook. However, the high rate of Outlook improved
kochia control compared to Roundup alone PRE.
This year, delaying Prowl or Prowl plus Outlook combinations
until the
flag leaf stage provided similar control to preemergence applications. If these treatments are as effective as the
PRE applications, then applications to flag leaf onions provide an
increased
level of crop safety compared to PRE applications.
Treatments with Prowl applied PRE or to flag leaf onions
followed
by applications of Outlook to two-leaf onions also effectively
controlled all
weeds. The Prowl label allows
applications to flag leaf onions and the Outlook label allows
applications to
two-leaf onions.
Roundup
alone PRE and Roundup plus Outlook (0.66 lb ai/acre)
produced higher medium onion yields and lower colossal, total, and
marketable
onion yields compared to all the other treatments (Table 2). The combination of Prowl plus Outlook PRE
had among the lowest number of onion bulbs per acre and was less than
plots
with Roundup alone PRE or applications of Prowl made to flag leaf
onions. This result illustrates the
potential to
reduce onion stand with PRE applications of soil-active herbicides. Even with the reduced number of onion bulbs,
this treatment produced yields similar to all other treatments. Only plots with reduced weed control had
significantly
lower yields. The increased weed
control and subsequent increase in onion yields from plots receiving a
PRE or
flag leaf application of a soil-active herbicide demonstrates the
importance of
soil-active herbicides for reducing weed germination and growth prior
to when postemergence
herbicide applications can be made.
Table
1. Onion injury and weed control in
response
to applications of Outlook®,
Nortron®,
and Prowl®,
Malheur Experiment
Station, Oregon State University, Ontario, OR, 2004.
|
|
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|
Injury |
Weed
control‡ |
|||||
|
Treatment |
Rate |
Timing* |
5-24 |
6-9 |
Pigweed† |
Common lambsquarters |
Hairy nightshade |
Kochia |
Barnyardgrass |
|
|
lb
ai/acre |
Leaf |
---------------------------------------------------------------%---------------------------------------------------------- |
||||||
|
Untreated |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
|
Roundup + Outlook Buctril + Goal Buctril + Goal Goal |
0.75 + 0.656 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
25 |
16 |
87 |
77 |
100 |
73 |
100 |
|
Roundup + Outlook Buctril + Goal Buctril + Goal Goal |
0.75 + 0.843 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
25 |
17 |
95 |
88 |
100 |
85 |
100 |
|
Roundup + Nortron 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 |
26 |
19 |
88 |
85 |
91 |
96 |
98 |
|
Roundup + Nortron Buctril + Goal Buctril + Goal Goal |
0.75 + 2.0 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
27 |
16 |
93 |
90 |
100 |
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 |
25 |
16 |
98 |
96 |
100 |
95 |
98 |
|
Roundup + Prowl Buctril + Goal Buctril + Goal Goal |
0.75 + 1.5 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
26 |
17 |
95 |
98 |
100 |
99 |
100 |
|
Roundup Buctril + Goal Buctril + Goal Goal |
0.75 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
25 |
16 |
84 |
77 |
98 |
69 |
99 |
|
Roundup + Prowl + Nortron Buctril + Goal Buctril + Goal Goal |
0.75 + 1.0 + 1.0 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
26 |
16 |
99 |
100 |
100 |
99 |
97 |
|
Roundup + Prowl + Outlook Buctril + Goal Buctril + Goal Goal |
0.75 + 1.0 + 0.843 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
26 |
18 |
97 |
100 |
95 |
98 |
100 |
Table
1 (continued). Onion injury and weed
control in response to applications of Outlook®,
Nortron®,
and Prowl®,
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 |
Barnyardgrass |
|
|
|
lb
ai/acre |
Leaf |
---------------------------------------------------------------%---------------------------------------------------------- |
|||||||
|
Roudup Prowl + Outlook Buctril + Goal Buctril + Goal Goal |
0.75 1.0 + 0.843 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE flag 2-leaf 3-leaf 5-leaf |
26 |
17 |
96 |
93 |
99 |
97 |
100 |
|
|
Roundup Prowl H2O + Outlook Buctril + Goal Buctril + Goal Goal |
0.75 1.0 + 0.843 0.125 + 0.125 0.25 + 0.125 0.25 |
PRE flag 2-leaf 3-leaf 5-leaf |
26 |
18 |
95 |
92 |
100 |
88 |
100 |
|
|
Roundup Prowl Buctril + Goal + Outlook Buctril + Goal Goal |
0.75 1.0 0.125 + 0.125 + 0.843 0.25 + 0.125 0.25 |
PRE flag 2-leaf 3-leaf 5-leaf |
25 |
16 |
88 |
83 |
97 |
100 |
100 |
|
|
Roundup Prowl H2O Buctril + Goal + Outlook Buctril + Goal Goal |
0.75 1.0 0.125 + 0.125 + 0.843 0.25 + 0.125 0.25 |
PRE flag 2-leaf 3-leaf 5-leaf |
26 |
17 |
92 |
92 |
100 |
100 |
100 |
|
|
Roundup + Prowl Buctril + Goal + Outlook Buctril + Goal Goal |
0.75 + 1.0 0.125 + 0.125 + 0.843 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
24 |
17 |
97 |
98 |
100 |
100 |
99 |
|
|
Roundup + Prowl Buctril + Chateau + Outlook Buctril + Goal Goal |
0.75 + 1.0 0.125 + 0.063 + 0.843 0.25 + 0.125 0.25 |
PRE 2-leaf 3-leaf 5-leaf |
39 |
27 |
98 |
100 |
100 |
100 |
96 |
|
|
LSD (0.05) |
-- |
-- |
2 |
3 |
12 |
12 |
6 |
10 |
3 |
|
*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 was evaluated on September 2.
‡Pigweed
is a
combination of redroot pigweed and Powell amaranth.
Table 2. Onion yield
in response to applications of Outlook®,
Nortron®,
and Prowl®,
Malheur Experiment
Station, Oregon State University, Ontario, OR, 2004.
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