Malheur Experiment Station Information for Sustainable Agriculture

HERBICIDE APPLICATION METHODS FOR CONTROL OF

YELLOW NUTSEDGE IN ONIONS^††

Corey V. Ransom, Charles A. Rice, and Joey K. Ishida

Malheur Experiment Station

Oregon State University

Ontario, OR, 2001

Introduction

Yellow nutsedge is extremely competitive with onions, and herbicide options for controlling yellow nutsedge in onions are limited. Dual Magnum is registered for controlling yellow nutsedge in onions grown in the Treasure Valley. Outlook has also been evaluated for this use. Dual Magnum has been applied in various ways and questions about the most effective application method led to this trial. In addition, yellow nutsedge tuber production and distribution in the soil were determined.

Application Methods for Yellow Nutsedge Control

This trial was conducted to determine the effect of application methods of Dual Magnum and Outlook on yellow nutsedge control and onion injury. The trial was established in a cooperators' field heavily infested with yellow nutsedge. Onions were planted on a 3.7-inch spacing in double rows on 22-inch beds on April 13. Plots were four rows wide and 30 ft long and arranged in a randomized complete block design with four replications.

Dual Magnum and Outlook were applied as a broadcast spray, a spray banded in the furrow, and sidedressed. In some treatments, initial applications of Dual Magnum or Outlook were followed with a second application of the same product or an application of Basagran plus crop oil concentrate (COC). Basagran plus COC was also applied twice for comparison. Initial herbicide applications were made on June 8, and second applications were made on July 6. At the first application, onions had three leaves and the yellow nutsedge was 6 inches tall. At the second application, onions had five leaves and the nutsedge was 10 inches tall. Nutsedge control was evaluated throughout the season. Because of poor onion establishment and heavy competition from the yellow nutsedge, onion injury was not evaluated and onion yields were not recorded from this trial.

Data were analyzed using analysis of variance and means were separated using a protected least significant difference at the 5 percent level, LSD (0.05).

Yellow Nutsedge Tuber Yield and Soil Distribution in Untreated Onions

On August 14, soil core samples were randomly taken from a 400-ft² area in a field with an extremely high yellow nutsedge population to determine the number, soil distribution, and production of tubers. The soil core probe had a 4.25-inch diameter and was 10 inches long. Soil cores were replicated four times. Soil from the core samples were separated into 2-inch increments. Soil was washed from the samples, and nutsedge tubers were collected and dried. Non-viable tubers (those that could be crushed easily between the fingers) were removed and the remaining tubers were counted and weighed.

Application Methods for Yellow Nutsedge Control

Poor onion stand and extreme yellow nutsedge competition prevented evaluation of onions for herbicide injury and onion harvest. On July 6, sidedress applications of Outlook provided greater yellow nutsedge control than broadcast or in-furrow banded applications (Table 1). Yellow nutsedge control with Dual Magnum was equal between application methods on this date. On July 13, Outlook or Dual Magnum sidedressed had greater yellow nutsedge suppression than when broadcast. On this date, treatments that had received Basagran had the highest yellow nutsedge control. On August 3, all plots with two applications, except for the two broadcast applications of Outlook, had significantly greater yellow nutsedge control than any of the single applications. On this date, treatments with single applications of Dual Magnum had greater control than Outlook treatments regardless of the application method. Adding COC to Dual Magnum and Outlook did not improve yellow nutsedge control.

Yellow Nutsedge Tuber Yield and Soil Distribution in Untreated Onions

Soil cores taken from various soil depths in 2001 showed similar trends in yellow nutsedge tuber numbers and biomass to those taken in 1999 and 2000 (Table 2). The majority of tubers were found in the top 2 inches of soil with tuber numbers decreasing with increasing soil depth (Fig. 1). The greatest weight of tubers was found in the top 4 inches of soil in 2001, whereas in 1999 the 4- to 6-inch soil layer had greater tuber biomass than the 0- to 2-inch layer. Total yellow nutsedge tuber numbers and biomass in 2000 and 2001 were approximately half of that in 1999.

Table 1. Yellow nutsedge control in response to herbicide application methods in onions, Malheur Experiment Station, Oregon State University, Ontario, OR, 2001.

				Yellow nutsedge control
Treatment	Rate	Timing*	Application method	7-6	7-13	8-3
	lb ai/acre	leaf		------------------------%----------------------
Dual Magnum	1.25	3-leaf	Sidedress	42	50	38
Outlook	0.64	3-leaf	Sidedress	44	35	15
Dual Magnum	1.25	3-leaf	Broadcast	38	25	30
Outlook	0.64	3-leaf	Broadcast	18	8	0
Dual Magnum	1.25	3-leaf	Band in furrow	38	38	22
Outlook	0.64	3-leaf	Band in furrow	26	22	10
Dual Magnum Dual Magnum	1.25 1.25	3-leaf 5-leaf	Sidedress Broadcast	73	51	71
Outlook Outlook	0.64 0.64	3-leaf 5-leaf	Sidedress Broadcast	58	58	62
Dual Magnum Dual Magnum	1.25 1.25	3-leaf 5-leaf	Broadcast Broadcast	36	43	63
Outlook Outlook	0.64 0.64	3-leaf 5-leaf	Broadcast Broadcast	28	25	37
Basagran + COC Basagran + COC	1.0 + 1% v/v 1.0 + 1% v/v	3-leaf 5-leaf	Broadcast Broadcast	23	88	65
Dual Magnum Basagran + COC	0.64 1.0 + 1% v/v	3-leaf 5-leaf	Broadcast Broadcast	34	88	78
Outlook Basagran + COC	0.64 1.0 + 1% v/v	3-leaf 5-leaf	Broadcast Broadcast	25	88	63
Dual Magnum + COC	1.25 +  1% v/v	3-leaf	Broadcast	35	35	25
Outlook + COC	0.64 + 1% v/v	3-leaf	Broadcast	27	24	10
Untreated				0	0	0
LSD (0.05)				15	14	18

* Treatments were applied to 3-leaf onions on June 8 and to 5-leaf onions on July 6.

Table 2. Yellow nutsedge tuber number and weight at various soil depths in 1999, 2000, and 2001, Malheur Experiment Station, Oregon State University, Ontario, OR.

	Tuber number Onion density				Tuber weight
Soil depth *	1999	2000	2001		1999	2000	2001
inches	---------------No./m2-------------				------------------g/m2---------------
0-2	7,325	2,842	5,494		242	177	308
2-4	5,758	1,941	3,526		360	161	325
4-6	3,644	1,312	984		430	151	127
6-8	1,640	820	82		175	85	7
8-10	1,385	109	246		112	30	12
LSD (0.05)	1,436	NS	1,904		168	NS	171
Total	19,752	7,024	10,332		1,319	604	779

*Samples were taken with a 4.25-inch diameter soil probe 10 inches long.

Figure 1. Relationship of yellow nutsedge tuber density and soil depth from combined data from samples taken in 1999, 2000, and 2001.

^††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  Monday February 26, 2007 .