1997 Weed Management Studies
Northern Research and Demonstration Farm
Kanawha, Iowa
Brent A. Pringnitz, extension program specialist,
and Robert G. Hartzler, associate professor,
Department of Agronomy.
Introduction
Several studies were conducted in corn and soybeans to evaluate commercially available herbicides for weed control and crop phytotoxicity. Various herbicide treatment combinations and application methods were evaluated.
Materials and Methods
The studies were established using a randomized complete block design with three replications. Plot size was 10 ft. by 25 ft. Herbicides were applied in 20 gallons of water per acre. Visual estimates of percentage weed control and crop injury data were made throughout June, July and August. Weed control observations are compared with an untreated control and made on a zero to 100 rating scale with zero percent equaling no weed control. Crop injury ratings are on a 0 to 100 rating scale, with 0 representing no crop injury. Weed species and populations are summarized in Tables 1 and 2.
Corn studies
Seedbed preparation included a spring disking. Crop residue on the soil surface at was 41 percent. The 1996 crop was soybeans. Corn was planted on April 29 at 28,600 seeds/A in 30 inch rows. Fertilization included 147 lbs/A actual N applied as urea. A cultivation of selected plots occurred on June 18. Herbicide application dates and crop stages are located in Table 1.
Soybean studies
Tillage included a fall chisel plowing of soybean residue and spring disking and field cultivation. Preplant (PPI) treatments were applied prior to planting and incorporated with two passes of a field cultivator operating 2 to 4 inches deep. Crop residue on the soil surface at planting was 28 percent. Soybeans were planted on May 13 at 175,000 seeds/A in 30 inch rows. Preemergence (PRE) treatments were applied at planting. Herbicide application information, crop stages, and weed populations can be found in Table 2.
Results and Discussion
In the comparison of Fall and Spring applied Dual II and Dual II Magnum (Table 3) the spring treatments provided significantly better grass control than Fall treatments. This was true across rates and different formulations. The July 1 evaluation shows that the Spring treatments were still providing acceptable control, whereas the Fall treatments were no longer controlling the foxtail. Table 5 compares a variety of preemergence and postemergence combinations. The POST and LPOST treatments generally provided better control than PRE and EPOST treatments. A comparison of treatments 13 and 14 shows the necessity of cultivation with Basis. Treatment 18 shows the effectiveness of a reduced rate of Accent in combination with cultivation in controlling foxtail.
Table 8 summarizes the evaluation of herbicide-tolerant soybeans. For both Roundup and Liberty, the earlier postemergence application resulted in significantly poorer foxtail control than later treatments or PRE/POST combinations. Yields were not collected for this study so the effect of weed competition is not known. The preemergence treatments in soybeans had reduced effectiveness due to the lack of timely rainfall (Table 9). Treatments with only postemergence treatments showed the most consistent control of grasses. However, many postemergence treatments also had significant crop injury at the first evaluation.
Table 1. Herbicide applications, crop stages, and weed populations in corn demonstrations, Kanawha.
Treatment / FALL / EPP / PRE / EPOST / POST/ MPOST / LPOSTDate / Nov. 5 / Apr. 15 / Apr. 29 / May 30 / June 10 / June 18
Sprayer
gpa / 20 / 20 / 20 / 20 / 20 / 20
psi / 32 / 32 / 32 / 32 / 32 / 32
nozzle / 11003 / 11003 / 11003 / 11003 / 11003 / 11003
Temperature (F)
air / 48 / 59 / 73 / 75 / 84 / 80
soil (4 inch) / 45 / 50 / 54 / 66 / 74 / -
Soil moisture / wet / dry / dry / moist / dry / dry
Wind (mph) / 5-8 NW / 7 SW / 0-3 NW / 4-6 E / 4 NW
Sky / cloudy / overcast / overcast / clear / part. cloudy / overcast
Relative humidity (%) / 83% / 34% / 21% / 47% / 25% / 52%
Corn growth
leaf no. / - / - / - / 2 / 5 / 8
height (inch) / - / - / - / 4 / 9 / 14
Foxtail
leaf no. / - / - / - / 2 / 3 / 5
height (inch) / - / - / - / 1 / 4-5 / 6-8
infestation (ft2) / - / - / - / 100 / 90 / 90
Smartweed
leaf no. / - / - / - / 2 / 4 / 6
height (inch) / - / - / - / 1.5 / 3 / 6
infestation (ft2) / - / - / 45 / 15 / 30
Lambsquarters
leaf no. / - / - / - / coty / 3 / 8
height (inch) / - / - / - / 0.5 / 1.5 / 6
infestation (ft2) / - / - / - / 0-10 / 2 / 3
Table 2. Herbicide applications, crop stages, and weed populations in soybean demonstrations, Kanawha.
Treatment / PRE/PPI / EPOST / POST/ MPOST / LPOST/ SPOSTDate / May 13 / June 13 / June 20 / June 26
Sprayer
gpa / 20 / 20 / 20 / 20
psi / 32 / 32 / 32 / 32
nozzle / 11003 / 11003 / 11003 / 11003
Temperature (F)
air / 45 / 85 / 80 / 81
soil (4 inch) / 45 / 72 / 70 / 75
Soil moisture / moist / dry / moist / dry
Wind (mph) / 3-5 NW / calm / 4 NW / 5 NW
Sky / overcast / clear / overcast / clear
Relative humidity (%) / 35% / 45% / 51% / 56%
Soybean growth
leaf no. / - / 1st trifol. / 2nd trifol. / 3-4th trifol.
height (inch) / - / 3 / 4 / 6-8
Foxtail
leaf no. / - / 3 / 5 / 5
height (inch) / - / 2.5 / 5 / 5
infestation (ft2) / - / 85 / 80 / 7-5
Common ragweed
leaf no. / - / 2 / 4 / 6
height (inch) / - / 2 / 4 / 6
infestation (ft2) / - / 9 / 7 / 5-10
Lambsquarters
leaf no. / - / coty. / 3 / 5
height (inch) / - / 1 / 2 / 4
infestation (ft2) / - / 3 / 2 / 1-5
Table 3. KC-DUAL - Evaluation of Fall and Spring applied Dual II and Dual II Magnum in corn, Kanawha.
# / Treatmenta / Rate / Unit / Time / 30 - May / 01- July
(prod./acre) / -- (% weed control) --
1 / Untreated check / 0 / 0
2 / Dual II Magnum (7.6EC) / 1.67 / pt / Fall / 73 / 63
3 / Dual II Magnum (7.6EC) / 2.0 / pt / Fall / 80 / 55
4 / Dual II (7.8EC) / 2.5 / pt / Fall / 67 / 53
5 / Dual II (7.8EC) / 3.0 / pt / Fall / 75 / 58
6 / Untreated check / 0 / 0
7 / Dual II Magnum (7.6EC) / 1.67 / pt / Spring / 86 / 73
8 / Dual II Magnum (7.6EC) / 2.0 / pt / Spring / 93 / 88
9 / Dual II (7.8EC) / 2.5 / pt / Spring / 92 / 83
10 / Dual II (7.8EC) / 3.0 / pt / Spring / 91 / 88
LSD (0.05) / 9 / 11
a All treatments received Buctril + Atrazine at 2 pts/A on June 18 for control of broadleaves.
Table 4. KC-PRE - Comparison of acetanilide herbicides for grass control in corn, Kanawha.
Trt. / Appl. / Foxtail# / Treatmenta / Rate / Unit / Time / 19-June
(prod./acre) / -- (% control) --
1 / Untreated Check / 0
2 / Dual Magnum (7.6EC) / 1.96 / pt / EPP / 67
3 / Topnotch (3.2CS) / 6.39 / pt / EPP / 77
4 / Frontier 6 (EC) / 1.56 / pt / EPP / 69
5 / Surpass (6.4EC) / 3.0 / pt / EPP / 78
6 / Harness (7EC) / 2.51 / pt / EPP / 62
7 / Axiom (68DF) / 24.0 / oz / EPP / 68
8 / Dual Magnum (7.6EC) / 1.31 / pt / PRE / 86
9 / Topnotch (3.2CS) / 4.26 / pt / PRE / 86
10 / Frontier 6 (EC) / 1.38 / pt / PRE / 92
11 / Surpass (6.4EC) / 2.0 / pt / PRE / 95
12 / Harness (7EC) / 1.71 / pt / PRE / 89
13 / Axiom (68DF) / 24.0 / oz / PRE / 79
14 / Untreated Check / 0
15 / Dual Magnum (7.6EC) / 1.47 / pt / EPP / 58
16 / Topnotch (3.2CS) / 4.79 / pt / EPP / 68
17 / Frontier 6 (EC) / 1.17 / pt / EPP / 67
18 / Surpass (6.4EC) / 2.25 / pt / EPP / 60
19 / Harness (7EC) / 1.88 / pt / EPP / 53
20 / Axiom (68DF) / 18.0 / oz / EPP / 65
21 / Dual Magnum (7.6EC) / 1.0 / pt / PRE / 82
22 / Topnotch (3.2CS) / 3.19 / pt / PRE / 82
23 / Frontier 6 (EC) / 1.04 / pt / PRE / 80
24 / Surpass (6.4EC) / 1.5 / pt / PRE / 85
25 / Harness (7EC) / 1.28 / pt / PRE / 79
26 / Axiom (68DF) / 24.0 / oz / PRE / 78
LSD (0.05) / 12
a All plots treated with Buctril + Atrazine at 2 pts/A on June 18 for control of broadleaves
Table 5. KC-POST - Evaluation of postemergence products and combinations in corn, Kanawha.
# / Treatment / Rate / Unit / Time / 01-July / 01-July
(prod./acre) / -- (% weed control) --
1 / Untreated Check / 0 / 0
2 / Balance (75DG) / 2.0 / oz / PRE / 45 / 70
3 / Balance (75DG) / 2.0 / oz / PRE / 82 / 75
Surpass (6.4EC) / 1.25 / pt
4 / Broadstrike + Dual (7.67SC) / 2.5 / pt / PRE / 55 / 59
5 / Dual II Magnum (7.6EC) / 2.0 / pt / PRE / 76 / 79
Action (4.75WP) / 2.97 / oz / POST
Beacon (75WG) / 0.38 / oz
Adjuvant - COC (EC) / 2.0 / pt
6 / Dual II Magnum (7.6EC) / 2.0 / pt / PRE / 78 / 91
Action (4.75WP) / 2.97 / oz / POST
Atrazine 4l (SC) / 2.0 / pt
Adjuvant - COC (EC) / 2.0 / pt
7 / Dual II (7.8EC) / 2.5 / pt / PRE / 70 / 85
Exceed 57 WDG (WG) / 0.8 / oz / POST
Adjuvant - COC (EC) / 1.0 / qt
Fertilizer - 28%UAN / 4.0 / qt
8 / Surpass (6.4EC) / 2.5 / pt / PRE / 82 / 90
Hornet (85.6DG) / 1.6 / oz / POST
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 2.0 / qt
9 / Harness (7EC) / 2.25 / pt / PRE / 85 / 83
Permit (75WG) / 0.66 / oz / POST
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 4.0 / qt
10 / Axiom (68DF) / 24.0 / oz / PRE / 58 / 90
Banvel (4SL) / 1.0 / pt / POST
11 / Harness (7EC) / 2.5 / pt / PRE / 82 / 74
Buctril + Atrazine (3SC) / 1.5 / pt / POST
12 / Surpass (6.4EC) / 2.0 / pt / EPOST / 73 / 91
Banvel (4SL) / 8.0 / oz
Accent (75WG) / 0.33 / oz
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 4.0 / qt
13 / Basis (75WG) / 0.33 / oz / EPOST / 75 / 92
Banvel (4SL) / 4.0 / oz
Adjuvant - COC (EC) / 1.0 / %
Fertilizer-21% Ammonium Sulfate / 4.0 / lbs
Cultivation
14 / Basis (75WG) / 0.33 / oz / EPOST / 45 / 87
Banvel (4SL) / 4.0 / oz
Adjuvant - COC (EC) / 1.0 / %
Fertilizer-21% Ammonium Sulfate / 4.0 / lbs
15 / Surpass (6.4EC) / 1.25 / pt / POST / 82 / 95
Basis Gold (89.5DF) / 14.0 / oz
Adjuvant - COC (EC) / 1.5 / %
Fertilizer - 28%UAN / 4.0 / qt
16 / Accent (75WG) / 0.66 / oz / POST / 90 / 96
Clarity (4SL) / 8.0 / oz
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 4.0 / %
17 / Accent (75WG) / 0.33 / oz / EPOST / 52 / 90
Clarity (4SL) / 4.0 / oz
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 4.0 / %
(continued on following page)
Table 5 (continued)
# / Treatment / Rate / Unit / Time / 01-July / 01-July
(prod./acre) / -- (% weed control) --
18 / Accent (75WG) / 0.33 / oz / EPOST / 80 / 95
Clarity (4SL) / 4.0 / oz
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 4.0 / %
Cultivation
19 / Accent (75WG) / 0.66 / oz / POST / 87 / 96
Buctril + Atrazine (3SC) / 2.0 / pt
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 2.0 / qt
20 / Accent (75WG) / 0.66 / oz / POST / 80 / 95
Scorpion III 84.3WG / 4.0 / oz
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 2.0 / qt
21 / Accent (75WG) / 0.33 / oz / POST / 90 / 95
Beacon (75WG) / 0.38 / oz
Banvel (4SL) / 2.0 / oz
Adjuvant - COC (EC) / 1.0 / qt
Fertilizer - 28%UAN / 4.0 / qt
22 / Aim (40DF) / 0.32 / oz / POST / 72 / 77
Aatrex Nine-O (90WG) / 8.89 / oz
Surfactant - Non-Ionic (SL) / 0.25 / %
Accent (75WG) / 0.66 / oz
LSD (0.05) / 12 / 17
Table 6. KC-PREP - Evaluation of postemergence application timing in corn, Kanawha.
Trt. / Appl. / Foxtail / P. Smartweed# / Treatment / Rate / Unit / Time / 01-July / 01-July
(prod./acre) / -- (% weed control) --
1 / Untreated Check / 0 / 0
2 / Surpass (6.4EC) / 1.88 / pt / PRE / 87 / 93
Buctril + Atrazine (3SC) / 2.0 / pt / EPOST
3 / Surpass (6.4EC) / 1.88 / pt / PRE / 75 / 93
Buctril + Atrazine (3SC) / 2.0 / pt / MPOST
4 / Surpass (6.4EC) / 1.88 / pt / PRE / 81 / 78
Buctril + Atrazine (3SC) / 2.0 / pt / LPOST
5 / Dual II (7.8EC) / 2.56 / pt / PRE / 55 / 90
Hornet (85.6DG) / 2.4 / oz / EPOST
Surfactant - Non-Ionic (SL) / 0.25 / %
6 / Dual II (7.8EC) / 2.56 / pt / PRE / 62 / 60
Hornet (85.6DG) / 2.4 / oz / MPOST
Surfactant - Non-Ionic (SL) / 0.25 / %
7 / Dual II (7.8EC) / 2.56 / pt / PRE / 58 / 85
Hornet (85.6DG) / 2.4 / oz / LPOST
Surfactant - Non-Ionic (SL) / 0.25 / %
8 / Accent (75WG) / 0.661 / oz / EPOST / 45 / 87
Banvel (4SL) / 1.0 / pt
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%Uan / 3.0 / qt
9 / Accent (75WG) / 0.661 / oz / MPOST / 85 / 95
Banvel (4SL) / 1.0 / pt
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 3.0 / qt
10 / Accent (75WG) / 0.661 / oz / LPOST / 90 / 96
Banvel (4SL) / 1.0 / pt
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 3.0 / qt
LSD(0.05) / 14 / 13
Table 7. KC-HRC - Postemergence treatments on herbicide resistant corn hybrids, Kanawha.
# / Treatment / Resist. / Rate / Unit / Time / 01-July / 01-July
(prod./acre) / --(% weed control) --
1 / Untreated Check / 0 / 0
2 / Liberty (1.67SL) / LL / 28.0 / oz / POST / 89 / 99
Atrazine 90(WG) / 13.33 / oz
Fertilizer-21% Ammonium Sulfate / 3.0 / lbs
3 / Liberty (1.67SL) / LL / 28.0 / oz / EPOST / 87 / 93
Fertilizer-21% Ammonium Sulfate / 3.0 / lbs
Liberty (1.67SL) / 20.0 / oz / POST
Fertilizer-21% Ammonium Sulfate / 3.0 / lbs
4 / Harness (7EC) / LL / 1.35 / pt / PRE / 96 / 99
Liberty (1.67SL) / 28.0 / oz / POST
Fertilizer-21% Ammonium Sulfate / 3.0 / lbs
5 / Marksman (3.2SC) / PP / 3.0 / pt / EPOST / 93 / 99
Poast Plus (1EC) / 1.0 / pt / POST
6 / Marksman (3.2SC) / PP / 3.0 / pt / POST / 53 / 95
Poast Plus (1EC) / 1.0 / pt
7 / Poast Plus (1EC) / PP / 1.7 / pt / POST / 73 / 93
Basagran (4SL) / 1.0 / pt
Atrazine 90 (WG) / 9.6 / oz
Adjuvant - COC (EC) / 0.625 / %
Fertilizer - 28%UAN / 1.25 / %
8 / Harness (7EC) / IMI / 1.25 / pt / PRE / 99 / 99
Lightning (70DG) / 1.28 / oz / POST
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 1.0 / qt
9 / Lightning (70DG) / IMI / 1.28 / oz / POST / 90 / 99
Banvel (4SL) / 1.0 / pt
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 1.0 / qt
10 / Resolve SG (75SG) / IMI / 5.33 / oz / POST / 95 / 97
Surfactant - Non-Ionic (SL) / 0.25 / %
Fertilizer - 28%UAN / 2.0 / qt
LSD (0.05) / 31 / 31
a Includes both waterhemp and pigweed species