Malheur Experiment Station
Oregon State University
Information for Sustainable Agriculture

PREEMERGENCE HERBICIDES FOR WEED CONTROL IN ONION††

Corey V. Ransom, Charles A. Rice, and Joey K. Ishida
Malheur Experiment Station
Oregon State University
Ontario, OR, 2003

Introduction

Weed control is essential for the production of marketable onions. Only a few herbicides are registered for preemergence application in onion. Effective preemergence herbicides can control weeds as they germinate and reduce the size and number of weeds that are present when onions are large enough to tolerate postemergence herbicide applications. This research evaluated registered and experimental herbicides for preemergence weed control in onion.

Methods

General Procedures

Trials were conducted at the Malheur Experiment Station under furrow irrigation. On March 28, onions (cv. 'Vaquero', Sunseeds, Parma, ID) were planted at a 3.7-inch spacing in double rows on 22-inch beds. Plots were four rows wide and 27 ft long and arranged in a randomized complete block design with four replicates. Lorsban was applied in a 6-inch band over each row at 3.7 oz/1,000 ft of row. Onions were sidedressed with 117 lb N, 72 lb P, 111 lb Sulfate, 114 lb S, 6 lb Zn, and 1 lb B/acre on June 3. Registered insecticides and fungicides were applied for thrips and downy mildew control. Herbicide treatments were applied with a CO2-pressurized backpack sprayer. Preemergence applications were applied at 20 gal/acre at 30 psi and postemergence treatments were applied at 40 gal/acre at 30 psi. All plots received Poast (sethoxydim) at 0.29 lb ai/acre plus crop oil concentrate (COC) (1.0% v/v) applied postemergence at 20 gal/acre and 30 psi on June 6. Weed control and onion injury were evaluated throughout the season. Onions were harvested September 17 and 18 and graded by size on September 23-25.Data were analyzed using analysis of variance and means were separated using a protected least significant difference (LSD) at the 5 percent level (0.05).
Preemergence Dacthal and Prowl

Preemergence-applied Prowl (pendimethalin) was compared to Dacthal (DCPA) 75 WP (a dry formulation) and Dacthal 6F (a liquid formulation). Combinations of Prowl plus Dacthal in two different ratios were also compared. Postemergence applications following preemergence Prowl and Dacthal combinations were similar with the exception of a comparison of Buctril (bromoxynil) plus Goal (oxyflurofen) to Buctril plus Valor (flumioxazin) applied to two-leaf onions.
Comparison of Preemergence Prowl, Nortron, and Outlook

Preemergence applications of Prowl, Nortron (ethofumesate), and Outlook (dimethenamid-P) in combination with Roundup (glyphosate) were evaluated for weed control and onion tolerance. Each product was evaluated at two rates. Combinations of Prowl with Nortron or Outlook were also evaluated. Preemergence treatments with soil-active herbicides were compared to plots where only Roundup was applied preemergence.

Results and Discussion


Preemergence Dacthal and Prowl

Preemergence Prowl gave greater than 89 percent control of all weed species and was more effective on nightshade than Dacthal alone (Table 1). There were no differences in weed control efficacy between the two Dacthal formulations. Certain combinations of Prowl plus Dacthal increased pigweed control compared to Dacthal alone but were not more effective than Prowl alone. Plots treated with Dacthal alone had reduced colossal, super colossal, and marketable onion yields compared to plots treated with Prowl alone or in combination with Dacthal (Table 2). The reduced yields were caused by weed competition.

Comparison of Preemergence Prowl, Nortron, and Outlook

Preemergence treatments were effective because of timely rain. No onion injury was observed from preemergence treatments (Table 3). Preemergence Prowl was most effective in controlling pigweed and hairy nightshade compared to Outlook or Nortron. Prowl significantly improved common lambsquarters control compared to Roundup alone. High rates of Outlook and Nortron gave lambsquarters control similar to Prowl but were not greater than Roundup alone or lower rates of Outlook or Nortron. Outlook did not increase hairy nightshade control compared to Roundup alone. Nortron increased nightshade control 45-60 percent and Prowl increased control 75-83 percent compared to Roundup alone. In past trials at the Malheur Experiment Station, Prowl has been much weaker on hairy nightshade. Preemergence Outlook did not increase marketable onion yields compared to Roundup alone (Table 4). In general, both Nortron and Prowl increased marketable onion yields compared to Outlook or Roundup alone.

Table 1. Onion injury and weed control in response to preemergence Dacthal and Prowl and different postemergence herbicide treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.






Weed control



Injury
Pigweed† Common lambsquarters Hairy nightshade
Treatment Rate Timing* 6-30
6-30 8-14 6-30 8-14 6-30 8-14

lb ai/acre Leaf ---------------------------------------------------------------- % -----------------------------------------------------------------
Untreated -- -- -
- - - - - -
Roundup + ProwlBuctril + GoalBuctril + GoalGoal 0.75 + 1.00.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5
100 90 100 100 99 89
Roundup + Dacthal 75 WPBuctril + GoalBuctril + GoalGoal 0.75 + 7.50.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5
94 83 98 90 78 45
Roundup + Dacthal 6FBuctril + GoalBuctril + GoalGoal 0.75 + 7.50.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5
98 81 99 92 78 54
Roundup + Prowl + DacthalBuctril + GoalBuctril + GoalGoal 0.75 + 0.75 + 5.60.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5
100 90 100 100 93 90
Roundup + Prowl + DacthalBuctril + GoalBuctril + GoalGoal 0.75 + 0.6 + 3.80.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5
100 97 100 100 95 84
Roundup + Prowl + DacthalBuctril + ValorBuctril + GoalGoal 0.75 + 0.75 + 5.60.125 + 0.0630.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5
100 97 100 99 100 97
Roundup + Prowl + DacthalBuctril + ValorBuctril + GoalGoal 0.75 + 0.6 + 3.80.125 + 0.0630.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 6
100 95 100 100 98 96
LSD (0.05)

NS
4 9 2 9 5 22
*Preemergence (PRE) treatment applied on April 11, two-leaf (2-leaf) on May 16, three-leaf (3-leaf) on May 27, and four-leaf (4-leaf) on June 9.
†Pigweed is a combination of redroot pigweed and Powell amaranth

Table 2. Onion yield in response to preemergence Dacthal and Prowl and different postemergence herbicide treatments, Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.

Onion yield
Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable

lb ai/acre Leaf -------------------------------------------------------------- cwt/acre -----------------------------------------------------------
Untreated -- -- 14 0 0 0 0 14
Roundup + ProwlBuctril + GoalBuctril + GoalGoal 0.75 + 1.00.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 4 10 651 551 106 1322
Roundup + Dacthal 75 WPBuctril + GoalBuctril + GoalGoal 0.75 + 7.50.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 8 22 763 254 23 1070
Roundup + Dacthal 6FBuctril + GoalBuctril + GoalGoal 0.75 + 7.50.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 6 22 794 272 22 1116
Roundup + Prowl + DacthalBuctril + GoalBuctril + GoalGoal 0.75 + 0.75 + 5.60.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 5 12 704 497 125 1343
Roundup + Prowl + DacthalBuctril + GoalBuctril + GoalGoal 0.75 + 0.6 + 3.80.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 3 14 740 463 59 1279
Roundup + Prowl + DacthalBuctril + ValorBuctril + GoalGoal 0.75 + 0.75 + 5.60.125 + 0.0630.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 0 14 622 521 94 1253
Roundup + Prowl + DacthalBuctril + ValorBuctril + GoalGoal 0.75 + 0.6 + 3.80.125 + 0.0630.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 1 15 674 555 82 1326
LSD (0.05)

5 14 106 138 63 123
*Preemergence (PRE) treatment applied on April 11, two-leaf (2-leaf) on May 16, three-leaf (3-leaf) on May 27, and four-leaf (4-leaf) on June 9.

Table 3. Onion injury and weed control in response to preemergence Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.



Weed control



Injury
Pigweed† Common lambsquarters Hairy nightshade
Treatment Rate Timing* 6-30
6-30 8-14 6-30 8-14 6-30 8-14

lb ai/acre Leaf ----------------------------------------------------------------- % ----------------------------------------------------------------
Untreated -- -- -
- - - - - -
Roundup Buctril + GoalBuctril + GoalGoal 0.750.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 10
80 71 86 88 65 18
Roundup + OutlookPOST Program 0.75 + 0.66same PRE2, 3, 4-leaf 10
86 74 89 88 77 37
Roundup + OutlookPOST Program 0.75 + 0.84same PRE2, 3, 4-leaf 10
89 80 86 96 75 14
Roundup + NortronPOST Program 0.75 + 1.0same PRE2, 3, 4-leaf 10
85 80 91 88 84 63
Roundup + NortronPOST Program 0.75 + 2.0same PRE2, 3, 4-leaf 10
91 76 98 98 95 78
Roundup + ProwlPOST Program 0.75 + 1.0same PRE2, 3, 4-leaf 10
100 96 100 100 99 93
Roundup + ProwlPOST Program 0.75 + 1.5same PRE2, 3, 4-leaf 10
100 99 100 100 100 100
Roundup + Prowl + NortronPOST Program 0.75 + 1.0 + 1.0same PRE2, 3, 4-leaf 10
100 98 100 100 100 100
Roundup + Prowl + OutlookPOST Program 0.75 + 1.0 + 0.84same PRE2, 3, 4-leaf 10
100 98 100 100 100 99
LSD (0.05)

NS
5 8 4 11 6 22
*Preemergence (PRE) treatment applied on April 11, two-leaf (2-leaf) on May 16, three-leaf (3-leaf) on May 27, and four-leaf (4-leaf) on June 9.
†Pigweed is a combination of redroot pigweed and Powell amaranth

Table 4. Onion yield in response to preemergence Outlook, Nortron, and Prowl, Malheur Experiment Station, Oregon State University, Ontario, OR, 2003.

Onion yield
Treatment Rate Timing* Small Medium Jumbo Colossal S. Colossal Marketable

lb ai/acre Leaf -------------------------------------------------------------- cwt/acre --------------------------------------------------------------
Untreated -- -- 16 0 0 0 0 16
Roundup Buctril + GoalBuctril + GoalGoal 0.750.125 + 0.1250.25 + 0.1250.25 PRE2-leaf3-leaf4-leaf 15 88 624 85 3 815
Roundup + OutlookPOST Program 0.75 + 0.66same PRE2, 3, 4-leaf 9 62 706 187 12 976
Roundup + OutlookPOST Program 0.75 + 0.84same PRE2, 3, 4-leaf 6 50 697 151 6 910
Roundup + NortronPOST Program 0.75 + 1.0same PRE2, 3, 4-leaf 4 151 772 243 16 1188
Roundup + NortronPOST Program 0.75 + 2.0same PRE2, 3, 4-leaf 5 48 675 348 41 1117
Roundup + ProwlPOST Program 0.75 + 1.0same PRE2, 3, 4-leaf 7 21 734 372 68 1201
Roundup + ProwlPOST Program 0.75 + 1.5same PRE2, 3, 4-leaf 5 15 794 351 55 1221
Roundup + Prowl + NortronPOST Program 0.75 + 1.0 + 1.0same PRE2, 3, 4-leaf 3 13 799 368 35 1218
Roundup + Prowl + OutlookPOST Program 0.75 + 1.0 + 0.84same PRE2, 3, 4-leaf 4 18 806 381 53 1262
LSD (0.05)

7 129 193 170 47 192
*Preemergence (PRE) treatment applied on April 11, two-leaf (2-leaf) on May 16, three-leaf (3-leaf) on May 27, and four-leaf (4-leaf) on June 9.

††The information in this report is for the purpose of informing cooperators in industry, colleagues at other universities, and others of the results of research in field crops. Reference to products and companies in this publication is for the specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable. Nor should any information and interpretation thereof be considered as recommendations for the application of any pesticide. Pesticide labels should always be consulted before any pesticide use.

 

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Last updated  Wednesday September 13, 2006 .