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 USING 28% N
SOLUTION
Richard Greenland
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 Buctril 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. Oftentimes 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. Research in Canada showed that liquid ammonium nitrate sprayed before the two true leaf stage of onion killed some weeds and did not hurt the onions. But the most common N solution available in this area, 28-0-0 (28% N), was not tested in that study. In this study we tested 28% N at three N rates (45, 60, and 75 lbs N/acre), three times of N application (when onions had 1, 1½, or 2 true leaves), and whether the Buctril + Goal herbicide application, usually applied when the onions have 2 true leaves, could be skipped if we used 28% N solution as a herbicide when the onions had up to two true leaves.
Table 52. Weed control ratings and onion growth (individual treatments).
Table 53. Yields and size of onions (individual treatments).
Table 54. Weed control ratings and onion growth.
Table 55. Yields and size of onions (averaged over variables).
MATERIALS AND METHODS
| Soil: | Maddock sandy loam and Egeland loam; pH=7.3; 2.5% organic matter; soil-P and soil-K were very high; soil-S was very low. |
| Previous crops: | 1997 - carrot; 1996 - sweet corn; 1995 - cabbage and broccoli. |
| Seedbed preparation: | Disked on 31 October 1997. Multiweeded (field cultivated) on April 13 to incorporate fertilizer and smooth the seedbed. |
| Planting: | Direct seeded onions (200,000 seeds/acre) on April 15 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 Poast + Dash (1.5 pt/acre + 1 qt/50 gal) on May 19 or Fusilade + crop oil concentrate (16 oz/acre + 1¾ pt/acre) on May 21 to kill the barley cover crop. |
| Plots: | Plots were 17 ft long by 6 ft wide on 8 ft centers (giving a 2-ft check between plots). The study had 4 reps. |
| Fertilizer: | On April 13, broadcast 14 lbs N/acre and 70 lbs
P2O5/acre as 10-50-0, 16 lbs N/acre and 19
lbs S/acre as 21-0-0-24, and 94 lbs K20/acre as 0-0-60.
Nitrogen treatments were broadcast sprayed on: May 18 (onions 2 to 3 inches tall with 1 true leaf, weeds ¾ inch tall); May 21 (onions 3 to 5 inches tall, 1½ true leaves, weeds ¼ to 1 inch tall); and May 28 (onions 3 to 5 inches tall, 2 true leaves, weeds ½ to 1½ inches tall). On May 27, urea was broadcast at 0, 15, 30, or 75 lbs N/acre to balance the N applied as a herbicide. Each plot received a total of 75 lbs N/acre as 28% N and/or urea. Sprayed 50 lbs N/acre as 28-0-0 on June 24. Fertigated 40 lbs N/acre as 28-0-0 on July 9. |
| Irrigation: | Overhead sprinkler irrigation as needed. |
| Pest control: | In addition to the 28% N used in the treatments, weeds were controlled with Prowl (1.5 pt/acre on May 11), Buctril + Goal (1.5 and 0.6 pt/acre on May 29 to plots not sprayed with 28% N, and on June 25 to all plots), Fusilade + nonionic surfactant (16 oz/acre + 1 pt/25 gal on June 25), and hand weeding. We sprayed with Ridomil (2.5 lbs/acre on June 26), Dithane (2.4 qt/acre on July 7), Manzate (3 lbs/acre on June 29, July 15, July 28 and Aug 13) and Rovral (1.5 pt/acre on July 23) to control diseases. No insect control needed. |
| Harvest: | Pulled onions approximately two weeks after half-down date. Onions were allowed to dry in the field until the first part of October when they were bagged and moved to a shed. The onions were graded Nov. 16 to Nov. 23. |
The 28% N solution burned the cotyledon leaf when applied when onions were in the 1 true leaf growth stage, but this did not seem to affect onion growth and development. The 28% N also slightly injured the onions when applied at the 2 true leaf stage. The onions receiving N earliest were taller and further along in development than those onions that received the late or no application of N solution. They also had higher yields and bigger onions. This was probably a nutrient response. We should have applied the urea earlier to balance the amount of N applied to each plot. The rate of 28% N applied made no difference except for redroot pigweed control, which was better at higher rates. Applying 28% N when onions had one to two true leaves did not control weeds sufficiently to be able to skip the Buctril + Goal herbicide application when the onions reached the two leaf stage.
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Table 52. Results of the 1998 onion weed control study at the Oakes Irrigation Research Site (individual treatments).
| Nitrogen Rate | Application timing† | Buctril+ Goal‡ | Weed control ratings | Onion injury June 2 | Growth stage§ June 2 | Onion height | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Lambsquarters | Redroot Pigweed | ||||||||||
| June 2 | June 25 | June 2 | June 25 | July 8 | June 2 | June 25 | |||||
| lbs/acre | # of leaves | ----------------------- 1 to 10 ----------------------- | # of leaves | --- inches ---- | |||||||
| 45 | 1 | Yes | --¶ | 10.0 a | -- | 8.0 bc | 9.8 | -- | -- | -- | 11.0 |
| 45 | 1 | No | 7.0 | 8.5 c | 5.8 | 4.5 efg | 7.1 | 0.3 | 2.1 | 6.3 | 11.5 |
| 45 | 1.5 | Yes | -- | 10.0 a | -- | 9.8 a | 10.0 | -- | -- | -- | 9.8 |
| 45 | 1.5 | No | 7.3 | 8.3 cd | 5.0 | 3.5 fg | 6.8 | 0.8 | 2.2 | 5.8 | 11.8 |
| 45 | 2 | Yes | -- | 10.0 a | -- | 10.0 a | 9.9 | -- | -- | -- | 9.0 |
| 45 | 2 | No | 6.0 | 8.8 bc | 6.3 | 4.3 efg | 7.5 | 1.8 | 1.9 | 4.1 | 10.3 |
| 60 | 1 | Yes | -- | 9.8 ab | -- | 9.0 ab | 9.8 | -- | -- | -- | 10.8 |
| 60 | 1 | No | 7.8 | 8.3 cd | 6.3 | 4.8 efg | 7.8 | 1.0 | 2.3 | 6.5 | 12.3 |
| 60 | 1.5 | Yes | -- | 10.0 a | -- | 9.8 a | 10.0 | -- | -- | -- | 11.3 |
| 60 | 1.5 | No | 7.5 | 9.2 abc | 4.5 | 3.7 efg | 7.5 | 0.5 | 2.3 | 6.3 | 12.0 |
| 60 | 2 | Yes | -- | 10.0 a | -- | 9.8 a | 9.9 | -- | -- | -- | 9.8 |
| 60 | 2 | No | 6.0 | 8.5 c | 6.3 | 5.0 def | 7.5 | 1.8 | 1.9 | 4.0 | 9.5 |
| 75 | 1 | Yes | -- | 10.0 a | -- | 9.0 ab | 10.0 | -- | -- | -- | 10.5 |
| 75 | 1 | No | 6.8 | 7.3 d | 7.5 | 4.8 efg | 8.0 | 0.5 | 2.3 | 6.3 | 12.0 |
| 75 | 1.5 | Yes | -- | 10.0 a | -- | 10.0 a | 10.0 | -- | -- | -- | 10.8 |
| 75 | 1.5 | No | 7.8 | 9.0 abc | 7.3 | 5.3 de | 8.1 | 0.8 | 2.3 | 5.9 | 12.0 |
| 75 | 2 | Yes | -- | 9.8 ab | -- | 9.8 a | 10.0 | -- | -- | -- | 9.0 |
| 75 | 2 | No | 6.3 | 8.3 cd | 8.0 | 6.5 cd | 9.0 | 2.5 | 1.9 | 3.8 | 10.3 |
| 0 | -- | Yes | -- | 10.0 a | -- | 9.5 ab | 10.0 | -- | -- | -- | 9.8 |
| 0 | -- | No | 5.0 | 8.5 c | 3.3 | 3.3 g | 6.6 | 1.5 | 1.8 | 4.0 | 10.0 |
LSD (0.05) |
NS | †† | 2.3 | †† | 1.3 | 0.8 | 0.2 | 0.9 | 1.8 | ||
C.V. (%) |
23 | 10 | 26 | 17 | 11 | 46 | 5 | 12 | 12 | ||
Probability of differences |
NS | *** | ** | *** | *** | *** | *** | *** | ** | ||
†The N treatments were applied when the onions had 1, 1.5, or 2 true leaves.
‡Half the plots received Buctril + Goal when onions had 3 true leaves. Other plots did not receive Buctril + Goal on this first application date. All plots received Buctril + Goal when the onions had 5 true leaves.
§The growth stage is given as the number of true leaves the onions had on June 2.
¶Buctril + Goal treatments were not applied before these ratings were taken so no ratings were taken from these plots.
††Values in the same column followed by the same letter are not significantly different at the 0.05 level.
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Table 53. Yields and size of onions in the 1998 onion weed control study at the Oakes Irrigation Research Site (individual treatments).
| Nitrogen Rate | Application timing† | Buctril + Goal‡ | Onion yield (given by onion diameter) | Bulb size | Total bulbs | ||||
|---|---|---|---|---|---|---|---|---|---|
| > 3" | 2¼ to 3" | >2¼ | <2¼ | total | |||||
| lbs/acre | # of leaves | ------------------------ cwt/acre ----------------------- | oz/bulb | 1000s/A | |||||
| 45 | 1 | Yes | 322 abc | 310 | 632 ab | 43 | 688 a-d | 6.1 abc | 181 |
| 45 | 1 | No | 237 bcd | 304 | 541 abc | 61 | 620 a-e | 5.5 bcd | 180 |
| 45 | 1.5 | Yes | 331 abc | 309 | 640 ab | 41 | 707 abc | 6.2 abc | 182 |
| 45 | 1.5 | No | 247 bcd | 337 | 584 ab | 57 | 655 a-d | 5.8 bcd | 182 |
| 45 | 2 | Yes | 136 d | 351 | 486 bc | 54 | 553 de | 5.0 cd | 176 |
| 45 | 2 | No | 191 cd | 309 | 500 bc | 61 | 581 cde | 5.2 cd | 178 |
| 60 | 1 | Yes | 333 abc | 302 | 635 ab | 44 | 710 ab | 6.4 ab | 177 |
| 60 | 1 | No | 297 a-d | 289 | 586 ab | 37 | 645 a-d | 6.1 abc | 169 |
| 60 | 1.5 | Yes | 414 a | 251 | 664 a | 29 | 720 a | 7.1 a | 165 |
| 60 | 1.5 | No | 309 a-d | 297 | 606 ab | 37 | 663 a-d | 6.3 abc | 171 |
| 60 | 2 | Yes | 389 ab | 266 | 656 a | 38 | 722 a | 6.5 ab | 179 |
| 60 | 2 | No | 171 cd | 326 | 498 bc | 70 | 582 cde | 5.2 cd | 183 |
| 75 | 1 | Yes | 327 abc | 275 | 601 ab | 39 | 659 a-d | 6.3 abc | 167 |
| 75 | 1 | No | 325 abc | 301 | 627 ab | 46 | 696 abc | 6.2 abc | 181 |
| 75 | 1.5 | Yes | 200 cd | 334 | 534 abc | 58 | 609 a-e | 5.5 bcd | 179 |
| 75 | 1.5 | No | 288 a-d | 313 | 601 ab | 37 | 669 a-d | 6.1 abc | 176 |
| 75 | 2 | Yes | 257 a-d | 298 | 555 abc | 40 | 609 a-e | 5.8 bcd | 166 |
| 75 | 2 | No | 161 cd | 326 | 487 bc | 67 | 568 cde | 5.1 cd | 180 |
| 0 | -- | Yes | 200 cd | 314 | 515 bc | 53 | 584 b-e | 5.4 bcd | 173 |
| 0 | -- | No | 143 d | 281 | 424 c | 67 | 506 e | 4.8 d | 167 |
LSD (0.05) |
§ | NS | § | NS | § | § | NS | ||
C.V. (%) |
44 | 18 | 17 | 38 | 14 | 15 | 8 | ||
Probability¶ |
* | NS | * | NS | * | * | NS | ||
†The N treatments were applied when the onions had 1, 1.5, or 2 true leaves.
‡Half the plots received Buctril + Goal when onions had 3 true leaves. Other plots did not receive Buctril + Goal on this first application date. All plots received Buctril + Goal when the onions had 5 true leaves.
§Values in the same column followed by the same letter are not significantly different at the 0.05 level.
¶Probability that values in the same column are the same. NS >5%. The *, **, and *** equal <5%, <1%, and <0.1%, respectively.
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Table 54. Results of the 1998 onion weed control study at the Oakes Irrigation Research Site (averaged over variables not listed in each section).
| Treatment | Weed control ratings | Onion injury June 2 |
Growth stage§ June 2 | Onion height | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Lambsquarters | Redroot Pigweed | |||||||||
| June 2 | June 25 | June 2 | June 25 | July 8 | June 2 | June 25 | ||||
| ------------------------ 1 to 10 ------------------------- | # of leaves | --- inches ---- | ||||||||
Nitrogen Rate |
||||||||||
| 45 lbs/acre | 6.8 | 9.3 | 5.7 | 6.7 b | 8.5 | 0.9 | 2.1 | 5.4 | 10.5 | |
| 60 lbs/acre | 7.1 | 9.3 | 5.7 | 7.0 ab | 8.7 | 1.1 | 2.1 | 5.6 | 10.9 | |
| 75 lbs/acre | 6.9 | 9.0 | 7.6 | 7.5 a | 9.2 | 1.3 | 2.1 | 5.3 | 10.8 | |
| LSD (0.05) | NS | NS | 1.4 | ‡‡ | 0.5 | NS | NS | NS | NS | |
Application Timing‡ |
||||||||||
| 1 leaf | 7.2 | 9.0 | 5.7 | 6.7 b | 8.7 | 0.6 | 2.2 | 6.3 | 11.3 | |
| 1.5 leaves | 7.5 | 9.2 | 5.7 | 7.0 ab | 8.7 | 0.7 | 2.3 | 6.0 | 11.3 | |
| 2 leaves | 6.1 | 9.4 | 7.6 | 7.5 a | 9.0 | 2.0 | 1.9 | 4.0 | 9.6 | |
| LSD (0.05) | NS | NS | NS | ‡‡ | NS | 0.4 | 0.1 | 0.5 | 0.7 | |
Buctril + Goal§ |
||||||||||
| No | --¶ | 8.4 | -- | 4.7 | 7.7 | -- | -- | -- | 11.3 | |
| Yes | -- | 9.9 | -- | 9.4 | 9.9 | -- | -- | -- | 10.2 | |
| Probability†† | - | *** | - | *** | *** | - | - | - | *** | |
C.V. (%) |
22 | 10 | 26 | 17 | 10 | 48 | 5 | 12 | 12 | |
†The growth stage is given as the number of true leaves the onions had on June 2.
‡The N treatments were applied when the onions had 1, 1.5, or 2 true leaves.
§Half the plots received Buctril + Goal when the onions had 3 true leaves. All plots received Buctril + Goal when the onions had 5 true leaves. This is a comparison between plots that did vs. did not receive Buctril + Goal when the onions had 3 true leaves.
¶Buctril + Goal treatments were not applied before these ratings were taken so these plots were not rated.
††The probability that there is a difference between the value for treatment vs. no treatment with Buctril + Goal. The difference is significant at the 0.05, 0.01, or 0.001 level for *, **, or ***, respectively.
‡‡Values in the same column and section followed by the same letter are not significantly different at the 0.05 level.
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Table 55. Yields and size of onions in the 1998 onion weed control study at the Oakes Irrigation Research Site (averaged over variables not listed in each section).
| Treatments | Onion yield (given by onion diameter) | Bulb size | Total bulbs | |||||
|---|---|---|---|---|---|---|---|---|
| > 3" | 2¼ to 3" | >2¼ | <2¼ | total | ||||
| ----------------------------- cwt/acre ---------------------------- | oz/bulb | 1000s/A | ||||||
| Nitrogen Rate | ||||||||
| 45 lbs/acre | 244 | 320 | 564 | 53 | 634 | 5.6 | 180 | |
| 60 lbs/acre | 318 | 289 | 606 | 43 | 672 | 6.2 | 174 | |
| 75 lbs/acre | 260 | 308 | 568 | 48 | 635 | 5.8 | 175 | |
| LSD (0.05) | NS | NS | NS | NS | NS | NS | NS | |
| Application Timing† | ||||||||
| 1 leaf | 307 a | 297 | 604 a | 45 | 670 a | 6.1 a | 176 | |
| 1.5 leaves | 297 a | 307 | 604 a | 43 | 669 a | 6.1 a | 176 | |
| 2 leaves | 218 b | 313 | 531 b | 55 | 603 b | 5.5 b | 177 | |
| LSD (0.05) | ¶ | NS | ¶ | NS | ¶ | ¶ | NS | |
| Buctril + Goal‡ | ||||||||
| No | 247 | 311 | 558 | 53 | 630 | 5.7 | 178 | |
| Yes | 301 | 299 | 600 | 43 | 664 | 6.1 | 175 | |
| Probability of difference§ | NS | NS | NS | * | NS | NS | NS | |
| C.V. (%) | 41 | 19 | 15 | 40 | 12 | 14 | 7 | |
†The N treatments were applied when the onions had 1, 1.5, or 2 true leaves.
‡Half the plots received Buctril + Goal when the onions had 3 true leaves. All plots received Buctril + Goal when the onions had 5 true leaves. This is a comparison between plots that did vs. did not receive Buctril + Goal when the onions had 3 true leaves.
§The probability that there is a difference between the value for treatment vs. no treatment with Buctril + Goal. The difference is significant at the 0.05, 0.01, or 0.001 level for *, **, or ***, respectively. NS means there was no significant difference.
¶Values in the same column and section followed by the same letter are not significantly different at the 0.05 level.
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Go to Oakes Irrigation Research Site Weed Control Studies page
Go to Oakes Irrigation Research Site 1998 annual report