Effects of Herbicide Application Timing on Field Grown Tulip, Narcissus, and Bulbous Iris
Timothy W. Miller and Carl R. Libbey
Washington State University, Mount Vernon Research & Extension Unit, Mount Vernon, WA
Weed control studies were conducted on ‘Merry Widow’ tulip, ‘Dutch Master’
daffodil, and ‘Blue Diamond’ iris at Washington State Univeristy Mount Vernon
beginning in the fall of 2000. Thiazopyr, pendimethalin, diuron, isoxaben, and
oryzalin were applied in combination with glyphosate or glufosinate. Application
timings were (1) all in the fall, (2) all in the spring (preemergence), (3) all in the
spring (early postemergence), (4) half in the fall/half in the spring (preemergence),
or (5) half in the fall/half in the spring (early postemergence). The spectrum and
efficacy of weed control and crop safety were evaluated.
Table 1. Weed control in ornamental bulbs treated with various herbicide combinations and timings.
Residual
herbicide
Nonselective
herbicidea
Timingb
Weed control
2/20/01 3/7/01 4/17/01 6/15/01
Thiazopyr
(0.75 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
---------------- % -----------------100
100
100
99
93
100
100
98
—
86
100
97
—
84
100
97
100
100
100
100
98
100
100
98
97
100
100
100
Diuron
(3.2 lbs/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
100
94
—
—
100
100
100
100
99
60
56
100
100
100
100
100
100
100
100
100
100
99
99
98
100
100
100
100
Isoxaben
(0.5 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
75
94
—
—
99
98
99
88
99
80
74
100
100
100
75
100
100
95
100
100
100
59
78
92
78
81
76
84
Pendimethalin
(3.0 lbs/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
97
91
—
—
98
97
99
99
99
75
88
100
100
100
100
100
100
98
100
100
100
94
96
96
94
97
97
98
Oryzalin
(0.75 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
99
91
—
—
98
98
100
100
93
83
89
100
100
100
100
96
100
95
100
100
100
96
89
97
92
96
96
98
17
12
ns
7
LSD0.05
a Glyphosate and
glufosinate applied at 0.75 lb/a.
bFall = all residual applied in fall; Spring = all residual applied in spring;
Fall + Spring = half residual applied in fall, half applied in spring; PRE = preemergence;
POST = postemergence.
Initial “fall” treatments were made on December 5, preemergence (PRE) to all
bulbs. The “spring” PRE treatments were made January 23, when iris averaged 3
inches tall and tulip and daffodil were just starting to emerge from soil (leaf tips
barely visible). Glyphosate was applied with the residual herbicide in these
treatments. The “spring” postemergence (POST) treatments with glyphosate were
made February 22 and with glufosinate February 27. Average iris height at this
timing was 5 inches, while daffodils were 3 inches, and tulip were 2 inches.
Table 2. ‘Merry Widow’ tulip injury after treatment with various herbicide combinations and timings.
Residual
herbicide
Nonselective
herbicidea
Timingb
Foliar
injury
3/7/01
Foliar Flower Flower
injury number height
4/17/01 4/17/01 4/17/01
Thiazopyr
(0.75 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
%
0
5
41
3
1
15
0
Diuron
(3.2 lbs/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
0
1
1
3
0
4
0
0
5
20
40
9
28
16
35
32
34
29
31
32
35
Isoxaben
(0.5 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
10
13
4
3
11
19
4
3
10
55
43
8
40
30
Pendimethalin
(3.0 lbs/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
3
1
4
4
0
43
1
Oryzalin
(0.75 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
LSD0.05
a Glyphosate
%
5
3
53
43
0
43
28
per plot inches
33
11
36
12
21
8
32
9
32
13
26
9
34
11
Weed control was estimated February 20 (PRE only), March 7, April 17, and June
15. Injury to bulb foliage was estimated March 7 and April 17. Flowers were
counted in each plot and height of five typical flowers was measured April 2
(daffodil), April 17 (tulip), and May 22 (iris). Bulbs were dug at maturity, then
cleaned, sorted, counted, and weighed. Tulip was more sensitive to herbicide
treatments than either daffodil or iris, so only tulip data are presented here.
Table 3. ‘Merry Widow’ tulip bulb yield after treatment with various herbicide combinations and timings.
Residual
herbicide
Nonselective
herbicidea
Timingb
Total
bulb
number
Total
bulb
weight
Average
bulb
weight
g/plot
796
664
480
427
680
523
527
g/bulb
5.3
4.6
4.1
4.0
4.7
4.0
4.0
Thiazopyr
(0.75 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
no./plot
149
143
122
111
146
134
132
13
11
10
9
12
10
11
Diuron
(3.2 lbs/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
179
157
124
115
167
139
150
1129
796
634
465
839
619
689
6.3
5.1
5.2
4.2
5.0
4.4
4.7
31
29
17
28
34
24
32
12
11
7
9
11
8
9
Isoxaben
(0.5 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
180
129
116
122
167
154
121
843
778
434
465
937
682
565
4.7
6.0
3.8
3.9
5.6
4.5
4.8
4
8
60
38
8
58
35
33
38
17
33
31
15
27
12
12
8
9
11
7
9
Pendimethalin
(3.0 lbs/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
183
191
133
120
181
129
145
991
1007
494
471
961
479
549
5.4
5.3
3.8
3.9
5.3
3.8
3.8
0
4
4
3
1
5
1
5
6
65
30
10
58
45
32
33
18
30
33
19
28
11
12
8
11
12
7
10
Oryzalin
(0.75 lb/a)
Glyphosate
Glyphosate
Glyphosate
Glufosinate
Glyphosate
Glyphosate
Glufosinate
Fall
Spring, PRE
Spring, POST
Spring, POST
Fall + Spring, PRE
Fall + Spring, POST
Fall + Spring, POST
175
166
137
128
166
145
123
913
930
549
553
985
561
521
5.3
5.6
4.0
4.3
6.0
3.9
4.7
6
13
8
2
33
180
1.0
and glufosinate applied at 0.75 lb/a.
bFall = all residual applied in fall; Spring = all residual applied in spring;
Fall + Spring = half residual applied in fall, half applied in spring; PRE = preemergence;
POST = postemergence.
LSD0.05
aGlyphosate
and glufosinate applied at 0.75 lb/a.
bFall = all residual applied in fall; Spring = all residual applied in spring;
Fall + Spring = half residual applied in fall, half applied in spring; PRE = preemergence;
POST = postemergence.
Based on single-season results, the following observations can be made:
(1) Fall treatments of residual herbicide + glyphosate were the safest for all bulb types, although weed control with isoxaben was
poor by springtime.
(2) Combinations with glyphosate applied all PRE in the spring to tulips were generally safe, except for isoxaben (foliar burn) and
diuron (yield response).
(3) Split isoxaben and oryzalin applications with glufosinate (POST) to tulips were generally safer than with glyphosate (POST).
(4) Spring applications of diuron to all bulb types should be used with caution.
(5) Pendimethalin, oryzalin, and thiazopyr combinations applied in the spring were hard on iris.
Spring PRE application of pendimethalin + glyphosate
POST application of pendimethalin + glufosinate
POST application of pendimethalin + glyphosate
This study is being repeated in 2001-02 to verify these results.