Purple Nutsedge Control with Imazaquin in Bermudagrass Turf

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Purple Nutsedge Control with Imazaquin in Bermudagrass Turf

Bul 408

B. J. Johnson and T. R. Murphy

Purple nutsedge [Cyperus rotundus (L.)] is one of the most difficult weeds to control in bermudagrass (Cynodon spp.) after the turf has been established (Coats et al. 1987). This weed is also a severe problem in many other grasses and crops in more than 90 countries of the world (Bendixen and Nandihalli 1987; Holm et al. 1977). In the United States, purple nutsedge is found in the Southeast from Texas to Virginia and in California (U.S. Department of Agriculture 1970). Purple nutsedge is a perennial which rarely reproduces by seed (Thullen and Keeley 1979), but reproduces extensively by rhizomes and tubers (Wills 1987).

Researchers and turfgrass managers have attempted to control purple nutsedge in turfgrasses for nearly three decades. Repeated postemergence applications of arsonate herbicides have given initial control (Hamilton 1971; Long et al. 1962; Sturkie 1967), but regrowth usually occurs. Foliage of purple nutsedge plants were killed by 2,4-D [(2,4-dichlorophenoxy)acetic acid], but new underground tubers began to sprout within three to four weeks (Loustalot et al. 1954). Bentazon {3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and perfluidone {[1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl]-methanesulfonamide} did not effectively control purple nutsedge in an earlier study in Georgia (Johnson 1975).

Bentazon is used by turfgrass managers for control of yellow nutsedge (Cyperus esculentus L.) but not for purple nutsedge. Imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5 -oxo-1H-imidazol-2-yl]-3-quino-linecarboxylic acid}. The herbicide has shown postemergence activity on purple nutsedge (Coats et al. 1987; Menn and Beard 1989).

Because purple nutsedge is difficult to control when growing with bermudagrass, experiments were initiated with imazaquin applied alone or with MSMA (monosodium salt of MAA) to determine the frequency of treatments needed to obtain effective control.

Materials and Methods

Three experiments were conducted on purple nutsedge control in an established mixed `Tifway' (C. dactylon x C. transvaalensis Burtt-Davy) and common bermudagrass [C. dactylon (L.) Pers.] turf with imazaquin applied alone or with MSMA from 1986 through 1988 at the Augusta National Golf Club, Augusta, GA. A fourth experiment was conducted on tolerance of common bermudagrass to imazaquin during 1989 and 1990 at the Georgia Station, Griffin, GA. Table 1 gives the time of treatments and ratings taken.

Table 1. Purple Nutsedge Experiments Conducted on Bermudagrass

Experiment	Type	Location	Date Applied	Date Rated
I	Annual imazaquin treatments	Augusta National Golf Club	1986: July 18 1987: July 17 1988: July 21	August 1,15 Oct. 2 July 13,28 August 12,31 July 21 August 4,15,30
II	Imazaquin formulations	Augusta National Golf Club	1987: July 13 1988: July 21	July 13,28 August 12,31 July 21 August 4,15,30
III	Multiple imazaquin treatments	Augusta National Golf Club	1987: June 1 July 14 1988: June 10 July 21	June 1,15 July 2,13,28 August 12,31 June 24 July 21 August 4,15,30
IV	Tolerance of common bermudagrass	Georgia Station, Griffin	1989: May 31 June 22 1990: May 30 June 22	June 5,14,22 June 29 July 6,12,18 June 5,11,18 June 21,28 July 3,8

Augusta National Golf Club

Experiment I. Imazaquin was applied alone and with MSMA as tank mixtures to purple nutsedge at rates given in table 2. Treatments were applied to the same plots on July 18 ± four days for three consecutive years (1986-1988). The purple nutsedge population was uniform with ground cover > 60% when the first treatments were made.

Experiment II. Imazaquin was applied as a liquid concentrate (LC) and granular (G) formulations to purple nutsedge on the same plots in 1987 and 1988. A tank-mixture of imazaquin LC plus MSMA was also included. Table 4 gives herbicide rates. Imazaquin G was formulated on a 27-3-3 fertilizer and contained 0.47 lb of imazaquin per 100 pounds of fertilizer. Whenever imazaquin is applied alone or with MSMA and no formulation is given, it will always be the LC formulation. Purple nutsedge population was uniform, with average cover of 37% when the first treatments were made.

Experiment III. Imazaquin was applied alone and with MSMA in multiple applications in 1987 and 1988. The first application was made June 5 ± five days, and the second application was made July 18 ± six days. Table 7 gives the rates and frequency of application. Treatments were made to different plots each year. The purple nutsedge population was uniform, with average cover of 47% when the first treatments were made.

Table 2. Influence of Imazaquin Applied Alone or with MSMA as a Single Annual Application for Three Consecutive Years on Purple Nutsedge Control in Experiment I at Augusta National Golf Club, Augusta, GA

Treatments^a		Purple nutsedge control^b
Treatments^a		1986			1987			1988
Herbicide	Rate lb ai/A	AUG 1	AUG 15	OCT 2	JULY 28	AUG 12	AUG 31	AUG 4	AUG 15	AUG 30
Untreated	-	0	0	0	0	0	0	0	0	0
Imazaquin	0.5	92	100	69	88	92	87	98	95	85
Imazaquin + MSMA	0.5 + 2.0	100	97	73	100	98	91	100	99	97
Imazaquin	0.38	82	88	47	80	77	70	95	91	77
Imazaquin + MSMA	0.38 + 2.0	100	99	87	100	98	94	100	100	100
Imazaquin	0.25	82	62	50	77	70	60	93	77	57
Imazaquin + MSMA	0.25 + 2.0	100	90	80	100	94	90	100	100	96
MSMA	2.0	35	42	35	37	38	30	48	30	33
LSD (0.05)		12	18	25	12	14	22	4	13	18

a. Herbicides were applied to the same plots July 18, 1986, July 14, 1987, and July 21, 1988.
b. Purple nutsedge control ratings were based on 0 = no control and 100 = complete control.

Table 3. Influence of Imazaquin Applied Alone or with MSMA as a Single Annual Application for Three Consecutive Years on Population of Purple Nutsedge in Experiment I at Augusta National Golf Club, Augusta, GA

Treatments^a		Purple nutsedge cover
Treatments^a		1986	1987		1988
Herbicide	Rate	Oct. 2	July 28	Aug 31	July 21	Aug 30
Untreated	-	62	25	62	45	67
Imazaquin	0.5	16	17	9	19	11
Imazaquin + MSMA	0.5 + 2.0	14	0	7	3	2
Imazaquin	0.38	28	23	25	25	17
Imazaquin + MSMA	0.38 + 2.0	6	0	4	3	0
Imazaquin	0.25	28	28	30	18	28
Imazaquin + MSMA	0.25 + 2.0	12	0	6	4	3
MSMA	2.0	30	28	42	33	42
LSD (0.05)		15	25	22	17	15

a. Herbicides were applied to the same plots on July 19, 1986, July 14, 1987,and July 21, 1988.

Table 4. Influence of Imazaquin Applied Alone or with MSMA as a Single Annual Application for Two Consecutive Years on Purple Nutsedge Control in Bermudagrass in Experiment II at Augusta National Golf Club, Augusta GA

Treatments^a		Purple nutsedge control^b
Treatments^a		1987			1988
Herbicide^c	Rate lb/ai/A	July 28	Aug 12	Aug 31	July 21	Aug 4	Aug 15	Aug 30
Untreated	-	0	0	0	0	0	0	0
Imazaquin LC	0.5	80	73	48	26	93	78	63
Imazaquin LC + MSMA	0.5 + 2.0	98	75	65	53	99	93	86
Imazaquin LC	0.38	73	73	45	26	88	67	50
Imazaquin LC + MSMA	0.38 + 2.0	95	78	62	52	100	94	86
Imazaquin G	0.38	80	68	53	50	88	81	69
Imazaquin LC	0.25	73	70	43	3	85	53	38
Imazaquin LC + MSMA	0.25 + 2.0	90	70	65	42	98	83	83
Imazaquin G	0.25	54	50	45	8	65	57	25
MSMA	2.0	43	33	50	13	49	13	27
LSD (0.05)		18	19	16	NS	8	20	16

a. Herbicides were applied to the same plots July 14, 1987 and July 21, 1988.
b. Purple nutsedge control ratings were based on 0 = no control and 100 = complete control.
c. LC = liquid concentrate, G = granular.

Georgia Station

Experiment IV. A weed-free, common bermudagrass turf was treated with imazaquin at 0.38 and 0.5 lb ai/acre in 1988 and 1990. The treatments were initially applied May 31 and repeated June 22 ± one day to the same plots both years. The normal time period between imazaquin applications for purple nutsedge control is at least a six-week interval. However, the repeated applications were made at three-week intervals in the present study to determine maximum turfgrass injury from imazaquin.

General information

Bermudagrass in all experiments was an established turf that was cut at a height of 1.0-1.25 inches once or twice per week. Purple nutsedge generally had four to six leaves at time of treatment. A normal fertility program for bermudagrass (annual 4 to 6 lb N/1000 ft²) was followed in all experiments. This included a balanced fertilizer (N-P-K) in early April and early September, with additional N applied as needed during late spring and summer. Irrigation was applied as needed to maintain a good quality turf.

Herbicides were applied in 25 and 40 gal water/acre at Augusta and Griffin, respectively. A surfactant (Alkylaryl-polyoxyethylene glycols fatty acid isopropanol) was added at 0.25% (v/v) with imazaquin. Extra surfactant was added to increase the surfactant concentration in MSMA treatments to 0.25%. The granular formulation was mixed with sand and applied by hand. The herbicide rates are presented as active ingredient per acre.

Table 5. Influence of Imazaquin Applied Alone or with MSMA as a Single Annual Application for Two Consecutive Years on Population of Purple Nutsedge in Experiment II at Augusta National Golf Club, Augusta, GA

Treatments^a		Purple nutsedge cover
Treatments^a		1987		1988
Herbicide^b	Rate	July 13	Aug 31	July 21	Aug. 30
Untreated	-	37	48	38	67
Imazaquin LC	0.5	50	32	28	27
Imazaquin LC + MSMA	0.5 + 2.0	53	20	18	10
Imazaquin LC	0.38	55	30	28	35
Imazaquin LC + MSMA	0.38 + 2.0	52	23	17	10
Imazaquin G	0.38	42	28	19	23
Imazaquin LC	0.25	50	37	37	42
Imazaquin LC + MSMA	0.25 + 2.0	43	22	22	15
Imazaquin G	0.25	52	38	35	48
MSMA	2.0	45	33	33	50
LSD (0.05)		NS	13	NS	11

a. Herbicides were applied to the same plots on July 14, 1987 and July 21, 1988.
b. LC = liquid concentrate, G = granular.

Visual estimates of bermudagrass injury, purple nutsedge control, and cover ratings were made at 2- to 3-week intervals as needed to show the maximum response to herbicides. At Griffin, bermudagrass injury ratings were made weekly. Bermudagrass injury ratings were based on 0 to 100, where 0 = no injury, 1-20 = slight injury, 21-30 = moderate injury, > 30 = severe injury and unacceptable, and 100 = complete kill. Purple nutsedge control ratings were based on 0 to 100, where 0 = no control and 100 = complete control. Purple nutsedge cover ratings were based on 0 to 100, where 0 = no purple nutsedge and 100 = complete plot coverage of purple nutsedge plants.

The experimental design was a randomized complete block with three replications. Plot size varied but was > 5 by 10 ft in all experiments. Analysis of variance using the Statistical Analysis System (General Linear Model Procedure) (SAS Institute 1982) was conducted. Due to year interactions, mean data are reported for each year. Means are separated by LSD at the 0.05 level.

Table 6. Influence of Sequential Imazaquin Treatments Applied Alone or with MSMA for Purple Nutsedge Control in Bermudagrass in Experiment III in 1987 at Augusta National Golf Club, Augusta, GA

Treatments^a		Purple nutsedge control^b				Bermudagrass injury^c
Herbicide	Rate lb ai/A	Application No.	Jun 15	July 13	July 28	Aug 31	Jun 15	July 28
Untreated			0	0	0	0	0	0
Imazaquin	0.25	1	75	55	10	27	5	0
Imazaquin	0.25	2	73	58	82	72	5	0
Imazaquin + MSMA	0.25 + 2.0	1	100	78	72	73	8	0
Imazaquin + MSMA	0.25 + 2.0	2	100	72	95	91	10	0
Imazaquin	0.38	1	85	79	42	50	8	0
Imazaquin	0.38	2	83	81	95	86	8	5
Imazaquin + MSMA	0.38 + 2.0	1	100	87	72	80	11	0
Imazaquin + MSMA	0.38 + 2.0	2	100	90	98	97	10	4
MSMA	2.0	1	41	12	20	30	0	0
MSMA	2.0	2	45	13	58	65	0	0
LSD (0.05)			8	14	22	22	3	NS

a. Herbicides were applied June 1, 1987 to all plots and July 14 to plots receiving a second application. The herbicides were applied at the given rates at each application.
b. Purple nutsedge control ratings were based on 0 = no control and 100 = complete control. Nutsedge population averaged 30% ground cover at the time first herbicide application was made and population in untreated plots increased to 47% when final ratings were made.
c. Bermudagrass injury ratings were based on 0 = no injury, 1-20 = slight injury, 21-30 = moderate injury, > 30 = severe injury and unacceptable, and 100 = complete kill.

Table 7. Influence of Sequential Imazaquin Treatments Applied Alone or with MSMA for Purple Nutsedge Control in Bermudagrass in Experiment III in 1988 at Augusta National Golf Club, Augusta, GA

Treatments^a			Purple nutsedge control^b				Bermudagrass injury^c
Herbicide	Rate lb ai/A	Application no.	Jun 24	July 21	Aug 4	Aug 30	Jun 24	Aug 8
Untreated	-	-	0	0	0	0	0	0
Imazaquin	0.25	1	86	47	10	18	3	0
Imazaquin	0.25	2	93	72	99	87	5	10
Imazaquin + MSMA	0.25 + 2.0	1	100	88	63