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, 1999
Richard Greenland
Table 39. Weed control and onion size and development.
Table 40. Number of onion bulbs and onion yield.
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 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 these 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) for weed control and its effect on the onions.
| Soil: | Maddock sandy loam, Embden sandy loam and Hecla sandy loam; pH=7.0; 2.7% organic matter; soil-P and soil-K were very high; soil-S was very low. |
| Previous crops: | 1998 - pepper; 1997 - carrot; 1996 - potato. |
| Seedbed
preparation: |
Disked on 27 October 1998. Field cultivated on April 12 to incorporate fertilizer and smooth the seedbed. |
| Planting: | Direct seeded 'Santos' onions (200,000 seeds/acre) on April 13 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 19 to kill the barley living mulch. |
| Plots: | Plots were 6 ft (four paired rows plus wheel track) wide (with a two foot wide border between plots) by 17 ft long. The study had 4 reps. |
| Fertilizer: | On April 7, broadcast 15 lbs N/acre and 75 lbs P2O5/acre as 10-50-0, 18 lbs N/acre and 20 lbs S/acre as 21-0-0-24, and 99 lbs K20/acre as 0-0-60. Applied 40 lbs N/acre as 28-0-0 on April 12. Sprayed 0, 45, 60 or 75 lbs N/acre as 28-0-0 on May 17 (when onions had one true leaf) and applied 75, 30, 15 or 0 lbs N/acre as urea on June 7 so all plots received a total of 75 lbs N/acre. |
| 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 19), Buctril + Goal (1.5 + 0.6 pt/acre on June 1 and June 16), and hand weeding. We sprayed with Kocide (2 lbs/acre on July 13 and July 23), Manzate (3 lb/acre on July 30), and Rovral (1.5 pt/acre on Aug 15) 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 Oct 1 when they were bagged and moved to a shed. The onions were graded Nov 15 to Nov 17. |
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The 28-0-0, at the 20 and 25 gals/acre rate (60 and 75 lbs N/acre), reduced growth of lambsquarters and pigweed, but did not satisfactorily control those weeds. The most striking result of this study was the response of the onions to the N fertilizer. Onion plant height, number of leaves, bulb size, and yield increased when 28-0-0 was sprayed on the onions. The onion response was greatest at a N rate of 60 lbs/acre.
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Table 39. Weed control and onion size and development in onion weed control / 28% N fertilizer study, 1999.
| Nitrogen rate† | Weed control ratings‡ | Onion | Final bulb size | Uniformity | Overall score | |||
| lambsquarters June 4 | red root pigweed July 19 | growth stage June 4 | height June 4 | height July 19 | ||||
lbs/acre |
0 to 10 | # of leaves | inches | oz/bulb | 1 to 5 | 1 to 10 | ||
| 0 | 1.7 b¶ | 5.2 b | 2.2 b | 4.3 c | 23.8 b | 5.7 c | 3.0 b | 7.0 b |
| 45 | 1.9 b | 6.6 a | 2.8 a | 5.0 b | 24.2 b | 7.0 b | 3.2 ab | 7.4 ab |
| 60 | 4.0 a | 7.6 a | 2.9 a | 5.8 a | 25.9 a | 7.9 a | 3.6 a | 7.6 a |
| 75 | 3.8 a | 7.1 a | 2.7 a | 5.3 b | 25.4 a | 7.8 ab | 3.5 a | 7.6 a |
| C. V. (%) | 54 | 18 | 10 | 8 | 4 | 12 | 11 | 7 |
| Probability | 0.0001 | 0.0001 | 0.0001 | 0.0001 | 0.0001 | 0.0001 | 0.0002 | 0.002 |
†Rates equal to 0, 15, 20, and 25 gal/acre of 28-0-0.
‡Weed ratings are from 0 to 10 with 0 equal to no control and 10 equal to no weeds.
¶Values in the same column followed by the same letter are not significantly different at the 0.05 level.
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Table 40. Number of onion bulbs and onion yield in onion weed control / 28% N fertilizer study, 1999.
| Nitrogen rate† | Number of onion bulbs | Onion yield | ||||||
| > 3" | 2¼ to 3" | < 2¼" | total | > 3" | 2¼ to 3" | < 2¼" | total | |
| lbs/acre | 1000s of bulbs per acre | cwt per acre | ||||||
| 0 | 29.8 c‡ | 46.5 a | 21.8 a | 108.1 | 167 c | 152 a | 28 a | 382 c |
| 45 | 45.9 b | 36.2 b | 12.6 b | 104.5 | 274 b | 124 b | 18 b | 458 b |
| 60 | 61.3 a | 31.0 b | 9.3 b | 115.5 | 380 a | 107 b | 13 b | 571 a |
| 75 | 56.1 ab | 30.1 b | 8.6 b | 105.5 | 348 a | 103 b | 12 b | 513 ab |
| C. V. (%) | 27 | 19 | 39 | 9 | 29 | 18 | 36 | 15 |
| Probability | 0.0001 | 0.0001 | 0.0001 | 0.16 | 0.0001 | 0.0001 | 0.0001 | 0.0001 |
†Rates equal to 0, 15, 20, and 25 gal/acre of 28-0-0.
‡Values in the same column 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 1999 annual report