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
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 at this onion growth stage killed some weeds and did not hurt the onions. But the most common N solution available in this area, 28-0-0, was not tested in that study. This study tested 28-0-0 for weed control and onion injury when applied at the one leaf growth stage of onion. We tested three rates (10, 15, and 20 gal of 28-0-0/acre) and three dilutions (undiluted, equal parts of 28-0-0 and water, and one part 28-0-0 to two parts water).
Table 29. Weed control ratings and yield
MATERIALS AND METHODS
| Soil: | Maddock sandy loam; pH=7.5; 2.7% organic matter; soil-P and soil-K were very high; soil-S was low. |
| Previous crops: | 1996 - cucumber and potato; 1995 - carrots; 1994 - sweet corn. |
| Seedbed preparation: | Disk twice April 24. Multiweeded (field cultivated) twice on April 24 to incorporate fertilizer and smooth the seedbed. |
| Planting: | Drilled barley cover crop on April 25 (1 bu/acre, 6-inch rows). Direct seeded 'Santos' onions on April 25 with a Stanhay vegetable planter at a population of about 200,000 seeds/acre. Planted in paired rows (3" apart), with the paired rows on 16" centers. Onions were planted parallel to the barley cover crop. |
| Plots: | Plots were 17 ft long by 6 ft wide on 8 ft centers (giving a 2-ft check strip between plots). The study had 4 reps. |
| Fertilizer: | On April 23, 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. Sprayed 50 lbs N/acre as 28-0-0 on April 24. Fertigated 52 lbs N/acre as 28-0-0 on July 11. |
| Irrigation: | Overhead sprinkler irrigation as needed. |
| Pest control: | Weed control treatments are given in Table 29. Sprayed all plots with Fusilade + Penetrate II (12 oz/acre + 1 pt/25 gal on May 29) to kill barley cover crop. Sprayed Prowl (1.5 pt/acre on May 27) and Buctril + Goal (1.5 pt/acre + 0.6 pt/acre on June 13) to control late weeds. Sprayed Bravo (1.5 pts/acre on Aug 5) and Dithane (2.2 qt/acre on Aug 20) for blotch control. No insect control needed. |
| Harvest: | Pulled Sept 25. Onions were allowed to dry in the field until Oct 7, when they were counted and weighed. |
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Table 29. Weed control and yield in the onion preliminary 28% N weed control study.
| Rate of 28% N | Dilution | Total solution | Rating on June 9 | Rating on Sep 24 | Yield | |||
| hairy nightshade | redroot pigweed | lambs- quarters | redroot pigweed | yellow foxtail | ||||
| gal/A | 28%:water | gal/A | ---------------------------- 0 to 10 --------------------------- | cwt/A | ||||
| 10 | 1:0 | 10 | 7 | 5 | 8 | 4.8 | 8.5 | 396 |
| 15 | 1:0 | 15 | 6 | 5 | 8 | 5.0 | 8.4 | 430 |
| 20 | 1:0 | 20 | 9 | 9 | 6 | 7.3 | 8.0 | 477 |
| 10 | 1:1 | 20 | 1 | 5 | 5 | 4.3 | 8.5 | 324 |
| 15 | 1:1 | 30 | 4 | 10 | 7 | 4.0 | 8.8 | 329 |
| 20 | 1:1 | 40 | 6 | 7 | 8 | 5.3 | 8.0 | 330 |
| 10 | 1:2 | 30 | 3 | 2 | 2 | 3.5 | 8.3 | 300 |
| 15 | 1:2 | 45 | 5 | 9 | 2 | 4.5 | 8.0 | 313 |
| 20 | 1:2 | 60 | 4 | 6 | 2 | 4.8 | 7.5 | 424 |
Averaged over dilutions |
||||||||
10 |
3.7 | 4.0 | 5.0 | 4.2 | 8.4 | 340 | ||
15 |
5.0 | 8.0 | 5.7 | 4.5 | 8.4 | 357 | ||
20 |
6.3 | 7.3 | 5.3 | 5.8 | 7.8 | 411 | ||
Averaged over N rates |
||||||||
| 1:0 | 7.3 | 6.3 | 7.3 | 5.7 | 8.3 | 435 | ||
| 1:1 | 3.7 | 7.3 | 6.7 | 4.5 | 8.4 | 328 | ||
| 1:2 | 4.0 | 5.7 | 2.0 | 4.3 | 7.9 | 345 | ||
| C.V.(%) | single plot observations | 40 | 15 | 38 | ||||
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RESULTS
Statistically, there were no differences between any of the treatments for weed control or yield. The observations on June 9 were only made on single plots so no statistics can be done. There are, however, some interesting trends. Pigweed and nightshade control seemed greater when we sprayed undiluted 28-0-0 at 20 gal/acre. The 28-0-0 also seemed to suppress these weeds at 15 gal/acre and at the low and medium dilution. Control of lambsquarters followed a similar, but much less clear, pattern. Foxtail did not seem to be effected much by the treatments. Yield was higher at low dilution and high N rates. The N application was not balanced by addition of N to plots receiving lower rates of N. This could have contributed to the higher yields at high N rates. We did not see any injury to the onions from the 28-0-0.
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