Oakes Irrigation Research Site
Carrington Research Extension Center * North Dakota State University
P.O. Box 531, Oakes, ND 58474-0531, Voice: (701) 742-2189, FAX: (701) 742-2700, email: rgreenla@ndsuext.nodak.edu

ONION WEED CONTROL STUDY, 2000

Richard Greenland

Results summary

Table 40. Herbicide treatments

Table 41. Weed control ratings

Table 42. Onion injury and characteristics of onions

Table 43. Number and yield of onions

Weed control is difficult in onions because onions do not compete well with weeds and few herbicides are available for onion production. A critical time for weed control is between onion emergence and the two true leaf stage. Weeds emerge and grow, but Buctrile and Goal cannot be applied during this time because they will injure the onions. There is no herbicide currently labeled to control weeds during this time. Often times the weeds have grown too large for Buctril and Goal to effectively control them when the herbicides are applied at the two true leaf stage. Late emerging weeds are not shaded by the onions and grow vigorously. Although they don't reduce yield much, they interfere with harvest. In this study we looked at 28% N as a possible herbicide when applied at the one leaf stage of onions. We also looked at some new herbicides, not yet labeled for use in onions, for weed control (especially late emerging weeds) and crop injury determinations.

MATERIALS AND METHODS

Soil: Maddock sandy loam; pH=7.1; 2.5% organic matter; soil-P and soil-K were very high; soil-S was high.
Previous crops: 1999 - pumpkin and squash; 1998 - field corn; 1997 - broccoli and cabbage.
Seedbed preparation: Disked on 29 October 1999. Multiweeded (field cultivated) on April 5 and April 17 to incorporate fertilizer and smooth the seedbed.
Planting: Direct seeded Teton onions (200,000 seeds/acre) on April 17 with a Stanhay vegetable planter modified to drill a barley cover crop (1 bu/acre, 6-inch rows) between and parallel to the onion rows. Planted onions in paired rows (3 inches apart), with the paired rows on 16-inch centers. Sprayed Fusilade + nonionic surfactant (12 oz/acre + 1 qt/50 gal) on May 18 to kill the barley cover crop.
Plots: Plots were 17 ft long by 6 ft (four paired rows plus wheel track) wide with a two foot border between plots. The study had 4 reps.
Fertilizer: On April 4, broadcast 18 lbs N/acre and 20 lbs S/acre as 21-0-0-24. Applied 50 lbs N/acre as 28-0-0 on April 12. Fertigated 35 lbs N/acre as 28-0-0 on June 27 and July 14. See Table 40 for additional N applications.
Irrigation: Overhead sprinkler irrigation as needed.
Pest control: In addition to the 28% N and other herbicides used in the treatments (See Table 40), weeds were controlled with Fusillade (1 pt/acre + non-ionic surfactant on May 18) and Buctril + Goal (1.5 + 0.6 pt/acre on May 31). We sprayed with Kocide (1.5 lbs/acre on July 20), Manzate (3 lb/acre on July 12 and 2 lb/acre on July 7, July 26, and Aug 2), and Bravo 500 (3 pt/acre on Aug 9 and 2 pt/acre on Aug 26) to control diseases. No insect control needed.
Harvest: Pulled onions Sept 14 to Sept 24 (approximately two weeks after half-down dates). Onions were allowed to dry in the field until September 29 when they were bagged and moved to a shed. The onions were graded Nov. 15 to Nov. 20.

RESULTS

Authority controlled pigweed, hairy nightshade, and lambsquarters early in the season, but lost control later. Frontier controlled pigweed early, but did not control late emerging pigweed unless a second application was made. It gave fair to poor (early and late) control of lambsquarters and fair to good control of hairy nightshade. Dual controlled pigweed, lambsquarters, and hairy nightshade. When applied at the two-true-leaf stage of onions, Dual controlled weeds throughout the rest of the season. A later application of Dual was not advantageous. The 28% N solution at 20 and 25 gal/acre increased pigweed control slightly and maybe not significantly. It did not help control lambsquarters and hairy nightshade.

Authority killed onions when applied preemergence. The destruction was slightly less when the application was delayed until just before onions emerged. In a border plot Authority injured onions less when we sprayed Authority when the onions had one true leaf, but the injury was still unacceptable. Spraying Authority when the onions have two to three true leaves is an option we will evaluate in the future. Frontier sprayed just after onions emerged caused slight damage, reduced onion plant height (at the 2X rate), slightly delayed maturity, and reduced onion stand, but did not reduce yield. Frontier or Dual, at the standard rates, sprayed when onions had two true leaves or later did not effect onion stand or yields. The 28% N solution did not affect onion stand or yield.

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Table 40. Herbicide treatments for the Oakes Irrigation Research Site 2000 onion weed control study.
Treatment number Herbicide(s) Rate Application timing1
1 Authority + 28% N 4 oz + 20 gal PRE1 + POST2
2 Authority + 28% N 8 oz + 20 gal PRE1 + POST2
3 Authority + 28% N 4 oz + 20 gal PRE2 + POST2
4 Authority + 28% N + Frontier 4 oz + 20 gal + 1 pt PRE1 + POST2 + POST3
5 Prowl + urea 1.5 pts + 130 lbs POST1 + POST2
6 Prowl + 28% N + urea 1.5 pts + 15 gal + 33 lbs POST1 + POST2 + POST2
7 Prowl + 28% N 1.5 pts + 20 gal POST1 + POST2
8 Prowl + 28% N 1.5 pts + 25 gal POST1 + POST2
9 Prowl + 28% N 3 pts + 20 gal POST1 + POST2
10 Prowl + 28% N + Prowl 1.5 pts + 20 gal + 1.5 pts POST1 + POST2 + POST3
11 Prowl + 28% N + Prowl 1.5 pts + 20 gal + 1.5 pts POST1 + POST2 + POST4
12 Frontier + 28% N 1 pt + 20 gal POST1 + POST2
13 Frontier + 28% N 2 pts + 20 gal POST1 + POST2
14 Frontier + 28% N + Frontier 1 pt + 20 gal + 1 pt POST1 + POST2 + POST4
15 Prowl + 28% N + Frontier 1.5 pts + 20 gal + 1 pt POST1 + POST2 + POST3
16 Prowl + 28% N + Frontier 1.5 pts + 20 gal + 1 pt POST1 + POST2 + POST4
17 Prowl + 28% N + Dual 1.5 pts + 20 gal + 2 pts POST1 + POST2 + POST3
18 Prowl + 28% N + Dual 1.5 pts + 20 gal + 4 pts POST1 + POST2 + POST3
19 Prowl + 28% N + Dual 1.5 pts + 20 gal + 2 pt POST1 + POST2 + POST4

1PRE1 was on April 21 (after planting, but before barley or onions emerged); PRE2 was on May 1 (after barley emerged but before onions emerged); POST1 was on May 5 (just after onions emerged); POST2 was on May 18 (urea) or May 22 and 23 (28% N) (onions had one true leaf); POST3 was on June 8 (onions had 3 true leaves); POST4 was on June 22 (onions had 4 to 5 true leaves). All plots sprayed with Fusilade (1 pt/acre + non-ionic surfactant) on May 18 (barley was 6 to 7 inches tall), and Buctril + Goal (1.5 + 0.6 pt/acre) on May 31 (onions had 2 true leaves).

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Table 41. Weed control ratings1 in the Oakes Irrigation Research Site 2000 onion weed control study.
Treatment2 number Redroot pigweed Hairy nightshade Lambsquarters
May 15 May 31 Aug 16 May 15 May 31 Aug 16 May 15 May 31
1 10.0 a3 10.0 a 7.8 d-g 10.0 a 10.0 a 8.8 bc 10.0 a 10.0 a
2 10.0 a 10.0 a 8.6 a-e 10.0 a 10.0 a 8.8 bc 10.0 a 10.0 a
3 10.0 a 10.0 a 8.3 b-f 10.0 a 10.0 a 8.8 c 10.0 a 10.0 a
4 10.0 a 10.0 a 7.9 d-g 10.0 a 10.0 a 9.3 abc 10.0 a 10.0 a
5 7.5 de 8.3 d 7.5 efg 8.0 bc 8.3 cd 10.0 a 8.8 bc 8.0 c
6 7.5 de 8.5 cd 7.0 g 7.8 bc 9.3 ab 9.8 a 9.3 b 8.8 bc
7 8.3 b-e 9.0 bcd 7.5 efg 8.0 bc 9.5 ab 10.0 a 9.3 b 9.3 ab
8 8.3 b-e 9.3 abc 8.0 c-g 7.3 c 9.5 ab 9.8 a 9.3 b 9.0 abc
9 7.3 de 9.3 abc 7.8 d-g 7.8 bc 9.5 ab 9.8 a 9.0 bc 9.3 ab
10 8.3 cde 8.8 bcd 8.0 c-g 7.8 bc 9.8 ab 9.3 abc 8.5 cd 8.3 bc
11 7.5 de 9.5 ab 8.5 a-e 8.3 bc 9.5 ab 10.0 a 9.3 b 9.3 ab
12 9.8 ab 9.5 ab 7.0 g 8.3 bc 7.5 d 9.3 abc 8.0 d 5.8 d
13 9.3 abc 10.0 a 7.1 fg 8.8 b 7.8 d 9.3 abc 8.5 cd 6.0 d
14 9.5 abc 10.0 a 9.4 ab 8.3 bc 7.8 d 9.8 a 9.0 bc 6.3 d
15 8.5 a-d 9.5 ab 8.8 a-d 8.0 bc 10.0 a 9.6 ab 9.0 bc 9.3 ab
16 8.3 b-e 8.8 bcd 9.4 ab 8.0 bc 9.5 ab 10.0 a 8.8 bc 8.8 bc
17 7.0 e 9.3 abc 8.8 a-d 8.3 bc 9.8 ab 10.0 a 9.0 bc 9.0 ab
18 8.0 cde 9.3 abc 9.1 abc 8.0 bc 9.5 ab 10.0 a 9.0 bc 9.0 abc
19 7.8 de 8.5 cd 9.5 a 7.8 bc 9.0 bc 10.0 a 9.0 bc 8.5 bc
C.V. (%) 6 3 5 5 4 3 2 4
Probability <.0001 <.0001 <.0001 <.0001 <.0001 0.016 <.0001 <.0001

1Ratings are from 0 to 10 with 0 equal to plot covered with large, vigorous weeds and 10 equal to no weeds in plot.

2See Table 40 for a description of the treatments.

3Values in the same column followed by the same letter are not significantly different at the 0.05 level. Data transformed using a square root transformation for analysis. Values presented as untransformed means.

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Table 42. Onion injury and characteristics of onions in the Oakes Irrigation Research Site 2000 weed control study.
Treatment1 number Onion injury Plant height June 27 Growth stage June 27 Days to half-down Single centered Uni-
formity
Overall appearance
May 15 May 31
------ 1 to 10 ----- inches # of true leaves % 1 to 5 1 to 10
1 9.0 d2 9.3 d 0.0 e 0.0 c --3 27 d 3.0 d 7.3 c
2 9.3 d 9.1 d 0.0 e 0.0 c --3 19 d 3.4 a-d 7.5 bc
3 6.5 c 5.8 c 7.0 d 3.6 b --3 25 d 3.1 cd 7.8 ab
4 9.3 d 9.5 d 0.0 e 0.0 c --3 75 abc 3.0 d 7.3 c
5 0.0 a 0.0 a 18.0 ab 6.4 a 120 a 70 abc 4.0 a 8.0 a
6 0.0 a 0.3 a 17.8 ab 6.4 a 120 a 65 bc 3.8 ab 8.0 a
7 0.0 a 0.3 a 17.5 ab 6.5 a 120 a 85 ab 3.9 ab 8.0 a
8 0.5 ab 0.3 a 16.8 ab 6.3 a 122 ab 80 ab 3.8 ab 7.8 ab
9 0.3 a 0.0 a 17.0 ab 6.4 a 121 ab 80 ab 3.9 ab 8.0 a
10 0.0 a 0.3 a 17.0 ab 6.5 a 120 a 85 ab 3.8 ab 8.0 a
11 0.0 a 0.5 ab 17.0 ab 6.5 a 121 ab 55 c 3.8 ab 8.0 a
12 0.5 ab 0.5 ab 16.8 ab 6.1 a 123 bc 65 bc 3.9 ab 7.8 ab
13 1.3 b 1.3 b 14.5 c 5.9 a 125 c 75 abc 3.8 ab 8.0 a
14 0.8 ab 0.5 ab 17.0 ab 6.3 a 121 a 75 abc 3.4 bcd 8.0 a
15 0.0 a 0.5 ab 17.0 ab 6.3 a 121 ab 70 abc 4.0 a 8.0 a
16 0.3 a 0.5 ab 18.0 ab 6.4 a 120 a 65 bc 3.9 ab 8.0 a
17 0.0 a 0.3 a 18.3 a 6.5 a 121 a 80 ab 3.9 ab 8.0 a
18 0.0 a 0.8 ab 16.3 bc 6.3 a 122 ab 90 a 3.6 abc 8.0 a
19 0.0 a 0.8 ab 17.3 ab 6.4 a 120 a 85 ab 3.8 ab 8.0 a
C.V. (%) 33 30 10 11 1 22 10 3
Probability <.0001 <.0001 <.0001 <.0001 0.007 0.0001 0.0016 0.0013

1See Table 40 for a description of the treatments.

2Values in the same column followed by the same letter are not significantly different at the 0.05 level.

3Onions in these treatments did not go down.

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Table 43. Number and yield of onions in the Oakes Irrigation Research Site 2000 weed control study.
Treatment number1 Number of onion bulbs harvested Onion bulb yield (by size)
> 3" 2¼ to 3" < 2¼ Total > 3" 2¼ to 3" < 2¼ Total
---------------- 1000s per acre ---------------- -------------------- cwt per acre ----------------
1 2 e2 2 g 0 c 5 g 14 f 6 g 0 c 23 e
2 1 e 0 g 0 c 2 g 11 f 2 g 0 c 16 e
3 24 d 13 g 4 c 45 f 184 de 47 g 7 c 251 d
4 1 e 1 g 0 c 3 g 7 f 4 g 0 c 15 e
5 40 bc 107 a 38 ab 203 ab 236 b-e 405 a 58 ab 737 a
6 42 b 101 abc 36 ab 196 abc 246 b-e 376 abc 55 ab 714 ab
7 34 bcd 109 a 39 ab 206 a 196 cde 397 ab 58 ab 698 abc
8 42 bc 100 abc 41 ab 203 abc 246 b-e 371 abc 63 a 716 ab
9 42 b 104 ab 40 ab 206 a 251 b-e 390 ab 61 a 745 a
10 28 cd 94 a-e 38 ab 180 cde 167 e 346 a-d 60 ab 611 c
11 43 ab 88 b-e 39 ab 186 a-e 250 b-e 324 cde 58 ab 666 abc
12 45 ab 77 def 31 b 171 de 277 abc 298 de 48 ab 663 abc
13 56 a 63 f 30 b 164 e 353 a 226 f 44 b 648 abc
14 47 ab 86 cde 32 b 181 b-e 287 ab 317 cde 49 ab 690 abc
15 44 ab 105 ab 37 ab 203 ab 262 bcd 392 ab 58 ab 747 a
16 43 ab 105 ab 35 ab 202 abc 256 bcd 391 ab 51 ab 741 a
17 36 bcd 106 a 40 ab 205 a 206 b-e 393 ab 58 ab 694 abc
18 42 b 76 ef 45 a 186 a-d 256 bcd 271 ef 61 a 631 bc
19 44 ab 95 a-d 38 ab 194 a-d 258 bcd 338 bcd 56 ab 686 abc
C.V.(%) 28 17 26 11 29 16 25 13
Probability <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001

1See Table 40 for a description of the treatments.

2Values in the same column followed by the same letter are not significantly different at the 0.05 level.

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