Kikuyugrass (Pennisetum clandestinum) Management in Turf1

DAVID W. CUDNEY, JAMES A. DOWNER, VICTOR A. GIBEAULT, J. MICHAEL HENRY, and JOHN S. REINTS2

Abstract. Kikuyugrass is an invasive, perennial weed of turf-grass in California. Currently, complete renovation of infested turf is the most practical means of control. A less disruptive method was needed to reduce the competitive ability of kikuyugrass while allowing the regrowth of desi_rable turf _spe~ies. Treatment with MSMA, triclopyr, and quinclorac did not control kikuyugrass as smgle apphcatlons, but when applied at 4- to 5-wk intervals over a 5-mo period, kikuyugrass was reduced. Sequential applications of two-way combinations of these herbicides in 1991 resulted in reductions of kikuyugrass from 80% to less than 1 % of the sward. Nomenclature: MSMA, monosodium salt of methylarsonic acid; quinclorac, 3,7-dichloro-8-quinolinecarboxylic acid; triclopyr, ((3,5,6-trichloro-2-pyrindinyl)oxy]acetic acid; kikuyugrass Pennisetum clandestinum Hochst. ex Chiov. #3 PESCL. Additional index words: Herbicide, suppress, competition, turf.

INTRODUCTION

Ki.kuyugrass is an ·extremely aggressive perennial weed of turf (3, 9). A native African weed, it is well adapted to warm, temperate climates such as the coast and inland valleys of southern and central California, as well as similar climatic regions of Hawaii, Australia, Mexico, and Africa. It eliminates competing desirable turfgrass species due to rapid stolon growth and aggres­sive thatch fonnation (1, 3, 7). Thus kikuyugrass is unsuitable for most turf uses such as golf fairways, parks, and home lawns ( 1, 6, 9). Kikuyu grass reproduces by seed and by vigorous stolons and rhi­zomes (2, 4, 5, 8).

There are currently no cultural or single, selective chemical methods to control kikuyugrass4• Complete renovation of the sward is an alternative that has been accomplished commercially. Two methods have been used. The first involves treatment with glyphosate [N­(phosphonomethyl)glycine] followed by thatch re­moval, reseeding, and treatment with PRE herbicides to control emerging ki.kuyugrass seedlings (1). The PRE

1Received for publication Apr. 24, 1992 and in revised form Nov. 25, 1992.

2Ex.t. Weed Sci.. Dep. 801. Plant Sci .. Univ. Calif., Rive~ide, CA92521; Farm Advisor. Ventura Co .. 702 County Squaic Dr., Ventura, CA 93003; Ex.1. Envir. Honie .. Dep. Bot. Plant Sci.. Univ. Calif., Rive~ide, CA 92521 : Farm Advisor. Orange Co., IOOO S. Harbor Blvd., Anaheim, CA 92805; Staff Res. Assoc., Dep. Bot. Plant Sci., Univ. Calif., Rive~idc, CA 92521.

3Leucrs following this symbol aic a WSSA-approved computet code from Composite List of Weeds, Revised 1989. Available from WSSA, 309 W. Clarie St., Champaign, IL 61820.

4Cudney, D. W. 1990. Unpublished data. 5Cudney, D. W. 1988 and 1990. Unpublished data.

180

herbicide used for this purpose in cool-season turf was siduron [N-2-methylcyclohexyl)-N'-phenylurea] (3), which is no longer registered for use in the United States. The second renovation method involves fumiga­tion followed by thatch removal and reseeding. Methyl bromide has been the preferred fumigant (3, 9).

Renovation is costly, varying from $1000.00 to $4500.00 per ha-1• Both renovation methods result in loss of turf use for several weeks while new desirable species are reestablished. After renovation, the desired turf species are again subject to a gradual infestation of kikuyugrass. · Y oungner reported that sequential POST applications

of MSMA were effective in reducing kikuyugrass inva­sion (6). MSMA, triclopyr, and later quinclorac had been shown to injure ki.kuyugrass5• Sequential applica­tions of POST herbicides, which injure but do not eliminate kikuyugrass as single applications, might be used to suppress the competitive ability of kikuyugrass and allow reestablishment of the desirable species. Se­quential applications would have an added advantage of allowing a gradual conversion of kikuyugrass-infested swards back to desirable species without loss of turf use. This would result in minimal utility loss and ecological disruption compared with fumigation and renovation.

Since kikuyugrass is a severe problem in turfgrass management, an experiment was initiated to compare single and sequential applications of several POST her­bicides and combinations of these herbicides for the selective control of invading kikuyugrass and the subse­quent reestablishment of desirable turf species.

Weed Technology. 1993. Volume 7:180-184

WEED TECHNOLOGY

MATERIALS AND METHODS

Four field experiments were conducted in the coastal and inland valleys of southern California from 1989 through 1991. These areas have a "Mediterranean" cli­mate with mild winters and summers (temperature rarely drops below O or exceeds 40 C). The plot areas were always well maintained with adequate fertility and moisture and mowed to a height of approximately 4 cm.

.Herbicide treatments were made in aqueous solutions with a COrpressurized backpack sprayer calibrated to deliver 280 L ha- 1 of spray mixture at a pressure of 207 kPa. Irrigation was withheld from the plots for 24 h after each herbicide treatment. All experiments were arranged in randomized complete block designs and replicated four times. Data were subjected to an analy­sis of variance, and means were separated using Fish­er's protected L.S.D. at P = 0.05. Kikuyugrass control. An initial experiment was estab­lished in the city of Ventura, CA on Aug. 1, 1989. The site had a mixed sward of perennial ryegrass (Lolium perenne L. # LOLPE) and Kentucky bluegrass (Poa pratensis L. # POAPR), which had been invaded by kikuyugrass. Kikuyugrass was uniformly distributed (83% of the turf cover) as was the remaining Kentucky bluegrass and perennial ryegrass. The treatment design was a two-way factorial. The first factor was a compari­son of single application and sequential applications (three applications each made 4 wk apart). The second factor was herbicide treatment and consisted of triclopyr (0.56 kg ha-1), MSMA (2.25 kg ha-1), and triclopyr plus MSMA (0.56 plus 2.25 kg ha-1). Plots were evaluated on Aug. 17, Sept. 18, Oct. 17, and on Nov. 13, 1989. Percent kikuyugrass control and phytotoxicity to the Kentucky bluegrass/perennial ryegrass mix was estimated relative to the control plots in each replication.

Two additional trials were established July; 1991 in the coastal region of southern California (Camarillo and Huntington Beach). Prior to treatment, both swards consisted of uniform mixes of approximately 85% kikuyugrass and 15% perennial ryegrass. The Hunting­ton Beach site was mowed to a height of 1 cm, raked, and seeded with perennial rye grass at 4.5 kg 100 m-2

(cv 'Manhattan II') on July 5, 1991. Four weeks later the sward was approximately 75% kikuyugrass and 25% perennial ryegrass when the first herbicide treat­ments were made. The Camarillo site was also seeded at 4.5 kg 100 m-2 with perennial ryegrass (cv Manhat-

Volume 7, Issue l (January-March) 1993

tan II), but seeding was done immediately after the first herbicide treatments were made on July 6, 1991. The herbicide treatments at both locations consisted of quin­clorac, MSMA, and triclopyr (0.56, 2.24, and 0.56 kg ha-I, respectively) as single and four sequential applica­tions made at 4- to 5-wk intervals. Two-way mixes with each possible combination of MSMA, triclopyr, and quinclorac (2.24, 0.56, and 0.56 kg ha-1, respectively) were also applied as four sequential treatments. Percent cover of kikuyugrass and perennial ryegrass was esti­mated at 2-wk intervals after the first treatment. An evaluation of the density of the kikuyugrass was made by counting rooted stems > 3 cm per 0.1 m2, 3 wk after the last herbicide application. Kikuyugrass-turfgrass competition. A test was con­ducted at the University of California, Riverside Ex­periment Station over a 2-yr period to measure the differences in competitive ability of kikuyugrass and six turf cultivars: perennial ryegrass (Manhattan II), Kentucky bluegrass (an unknown blend), tall fescue (Festuca arundinacea Schreb. 'Bonsai'), common ber­mudagrass [Cynadon dactylon (L.) Pers.], hybrid Ber­muda (C. dactylon x C. transvaalensis Burtt-Davy 'Santa Ana'), and zoysia (Zoysia japonica Steud. 'El Toro').

Stolons of kikuyugrass were pressed into a well prepared seedbed in October, 1989. A uniform, vigor­ous kikuyugrass stand had formed by June, 1990. Plugs (10 cm diam) were then removed from well established sods of the six turf species. Four plugs of each species were placed in separate 1.5- by 1.5-m sections of the kikuyugrass sward. The experiment was a randomized complete block with two-factor, factorial treatments. The first factor was turf species plugged and the second was herbicide treatment. After a 6-wk establishment period, the plots received their first herbicide treatment. The treatments consisted of MSMA (2.25 kg ha-1),

triclopyr (0.56 kg ha-1), MSMA plus triclopyr (2.25 plus 0.56 kg ha-1), and an untreated control. Three treatments were made in 1990, each at 6-wk intervals (July 14, Aug. 30, and Oct. 16). In 1991, quinclorac (0.75 kg ha-1) was included. Four applications were made at 6-wk intervals in 1991 (June 5, July 18, Sept. 2, and Oct. 15). Evaluations were made by measuring plug diameter of the six turf species at 6-wk intervals from August to November in each year. Kikuyugrass density was measured by counting the number of rooted stems with lengths of at least 3 cm per 0.1 m2 on Nov. 17 at the end of the experiment.

181

CUDNEY ET AL.: KIKUYUGRASS MANAGEMENT IN TURF

Table I . Effect of herbicide ueatments on kilcuyugrass control at Ventura, CA in I 989.

Rate of Kikuyugrass control

Treatment application Aug. 17, 1989 Sept. 18, 1989 Oct. 17, 1989 Nov. 13, 1989

kg ha-1 %

MSMA8 2.25 60 42 26 12 MSMAb 2.25 54 60 68 52 Triclopyr8 0.56 36 25 22 12 Triclopy~ 0.56 38 50 52 50 MSMA + Triclopyr8 2.25 ± 0.56 62 46 44 18 MSMA + Triclopy~ 2.25 ± 0.56 62 75 86 88 LSD (0.05f 8 7 4 8

8Single application made Aug. I, 1989.

bsequential applications made Aug. I, Sept. 4, and Oct. 3, 1989.

_ cLSD <?.0~) for intera~tion comparisons among means for single and sequential applications of herbicides. The comparison of means for sequential vs single apphcauon (not shown) was significant for Sept. 18, Oct. 17, and Nov. 13, 1989.

RESULTS AND DISCUSSION

Kikuyugrass control. MSMA, triclopyr, and MSMA + triclopyr controlled kikuyugrass somewhat initially as single applications, !Jut that effect declined with time (Table 1). Sequential applications of these treatments improved percent control with time. MSMA and triclopyr applied sequentially were similar in percent kikuyugrass control at the end of the test (52 and 50%, respectively). Sequential applications of MSMA + triclopyr controlled kikuyugrass best at the end of the test (88%). There was no significant injury from any of the treatments to the desired Kentucky bluegrass and perennial ryegrass mix except for slight discoloration and stunting which lasted less than 1 wk after each application (data not given). The desired species had

filled in the areas vacated by kikuyugrass and were dominant in the plots that had received the sequential MSMA + triclopyr treatments.

Sequential herbicide treatments in the 1991 trials controlled kikuyugrass and improved percent perennial ryegrass better than single herbicide treatments at the Huntington Beach and Camarillo locations (Table 2). When individual herbicides were compared, sequential applications of quinclorac reduced kikuyugrass density best (0.8 and 2.1, 3 cm stems per 0.1 m2 for Huntington Beach and Camarillo, respectively, versus the untreated, 170.8 and 140.1, 3-cm stems per 0.1 m2, respectively). Sequential applications of triclopyr ranked second in reducing kikuyugrass density (1.4 and 3.6, 3-cm stems per 0.1 m2); whereas, MSMA also reduced kikuyugrass

Table 2. Effects of single and sequential herbicide applications on establishment of perennial ryegrass and kikuyugrass density at the end of the 1991 growing season in Huntington Beach and Camarillo, CA.

Treatment

Quincloracb Quincloracc MSMAb MSMAC Triclopy~ Triclopyr Quinclorac + MSMA c Quinclorac + lriclopyr MSMA + lriclopyr Untreated LSD (0.05)

3Stems > 3 cm per 0.1 m2.

h-rreated at first application only.

cTrcated al all four applications.

182

Rate of application

kg ha-1

0 .6 0.6 2.2 2.2 0.6 0.6 0.6 + 2.2 0.6 + 0.6 2.2 + 0.6

Perennial ryegrass

%

59 97 56 92 55 96 99 98 98 30 14

Huntington Beach

Kikuyugrass density8

50.8 0.8

78.0 5.8

70.2 l.4 0 0 0

170.8 34.4

Perennial ryegrass

%

19 97 18 66 10 85

100 100 100

10 22

Camarillo

Kikuyugrass density1

106.4 2.1

107.1 26.4

128.6 3.6 0 0 0

140.1 39.0

Volume 7, Issue 1 (January-March) 1993

WEED TECHNOLOGY

Table 3. Performance of siit turfgrass cultivars affected by herbicide treatments grown in a ki.kuyugrass sod at Riverside, CA in 1990, year I.

Turf cultivarsa

Herbicide Rate of Tall Perennial Kentucky Common Hybrid Zoysia-treatment application fescue ryegrass bluegrass bermudagrass bermudagrass grass Meanb

kg ha-I cm diam

MSMA 2.25 9.3 JO.I 10.0 11.6 11.8 8.7 10.3 Triclopyr 0.56 9.7 10.5 10.2 8.9 11.2 10.3 10.3 MSMA + triclopyr 2.25 + 0.56 11.7 10.8 10.7 10.4 11.9 10.9 11.0 Control 7.5 8.4 7.9 7.9 9.2 7.7 8.1 Meanc 9.5 10.0 9.7 9.7 11.0 9.4

8LSD (0.05) for all interactions among cultivars and herbicide treatments = 1.3 cm.

bLSD (0.05) for herbicide treatment means = 0.9 cm.

cLSD (0.05) for turf cultivar means = 0.7 cm.

density (5.8 and 26.4, 3 cm stems per 0.1 m2 for Huntington Beach and Camarillo, respectively). The sequential two-way combinations of MSMA, triclopyr, and quinclorac eliminated kikuyugrass by the end of the season at both locations.

The percent perennial ryegrass in the plots was in­versely proportional to the density of kikuyugrass. Per­cent perennial ryegrass for sequential applications of quinclorac varied from 97 .0 to 97 .3 for Huntington Beach and Camarillo, whereas triclopyr varied from 95.8 to 85.0% and MSMA from 92.3 to 66.2%. Where kikuyugrass was completely controlled in the two-way combination treatments, percent perennial ryegrass var­ied from 98 to 100%. Kikuyugrass-turfgrass competition. Of the six culti­vars compared, hybrid bermudagrass had a greater overall mean plug diameter at the end of the first growing season (Table 3). When overall treatment ef­fects were compared, kikuyugrass competition had

reduced plug diameter, from the original 10 cm diam of the plugs at planting, to 8.1 cm in the control plots. Sequential herbicide treatment with MSMA, triclopyr, or MSMA plus triclopyr resulted in a maintenance of mean plug diameter (10.3, 10.3, or 11.0 cm, respective­ly). Within herbicide treatments, common ber­mudagrass was injured by triclopyr, resulting in a reduction in plug diameter (8.9 cm).

Hybrid bermudagrass, zoysiagrass, and tall fescue had greater overall mean plug diameters at the end of the second growing season (Table 4) than perennial ryegrass and Kentucky bluegrass (15.,7, 15.4, and 14.4 cm, compared with 12.7 and 12.7 cm, respectively). Common bermudagrass had the lowest mean plug di­ameter (10.3 cm); this was due to the phytotoxic effect of triclopyr on common bermudagrass (2.7 cm) which lowered the overall bermudagrass mean. Competition from the kikuyugrass sod had reduced the overall mean plug diameter for treatments in the control plots to 5 .6

Table 4. Performance of six turfgrass cultivars affected by herbicide treatments grown in a kikuyugrass sod at Riverside, CA in 1991, at the end of the second year.

Herbicide Rate of Tall Perennial Kentucky treatment application fescue ryegrass bluegrass

kg ha-1

MSMA 2.25 12.7 12.2 12.3 Triclopyr 0.56 14.4 12.0 12.4 MSMA + triclopyr 2.25 + 0.56 20.3 16.4 17.5 Quincloracc 0.75 17.3 16.0 15.5 Control 7.6 7.2 6.3 Meand 14.4 12.7 12.7

8LSD (0.05) for all interactions among cultivars and herbicide treatments = 3.9 cm.

bLSD (0.05) for herbicide treatment means = 1.9 cm.

cQuinclorac treatments were added within the plot area in 1991 only.

dLSD (0.05) for turf cullivar means = 1.7 cm.

Volume 7, Issue I (January-March) 1993

Turf cultivarsa

Common Hybrid Zoysia-bennudagrass bermudagrass grass Meanb

cm diam

13.8 17.8 15.5 14.0 2.7 11.3 3.3 9.3

16.0 21.3 24.9 21.1 17.5 19.0 21.5 17.8

1.7 8.9 2.1 5.6 10.3 15.7 15.4

183

CUDNEY ET AL.: KIKUYUGRASS MANAGEMENT IN TURF

cm. Within the control plots zoysiagrass and common bermuda were least competitive (plug diameters of 2.1 and 1.7 cm, respectively) whereas hybrid bermudagrass was most competitive (8.9 cm) followed by tall fescue, perennial rye grass, and Kentucky bluegrass (7 .6, 7 .2, and 6.3 cm).

Sequential herbicide application (Table 4) of MSMA plus triclopyr, quinclorac, or MSMA resulted in reduced kikuyugrass competition and increased plug growth when averaged over all turf cultivars (21.1-, 17.8-, and 14.0-cm plug diam, respectively). Sequential treatment with triclopyr alone resulted in injury to both common bermudagrass and zoysiagrass (plug diameters of 2.7 and 3.3 cm, respectively). Triclopyr did not injure tall fescue, perennial ryegrass, or Kentucky blue­grass (14.4, 12.0, and 12.4 cm) and was similar in performance to MSMA on those species. Triclopyr did not cause a reduction in the original 10-cm plug diam with hybrid bermudagrass (11.3 cm); however, that was the lowest plug diameter for herbicide treatment within that cultivar. Although triclopyr injured common ber­mudagrass and zoysiagrass, it was not as damaging to hybrid bermudagrass. The combination of MSMA and triclopyr did not injure these warm season species. The plug diameters of common bermudagrass, hybrid ber­mudagrass, and zoysiagrass increased in size over the 2-yr period (16.0, 21.3, and 24.9 cm, respectively) when treated sequentially with the combination. Appar­ently MSMA reduced the phytotoxicity of triclopyr on these species. Quinclorac was used only in the second season; however, it did not injure either the cool season or the warm season species and plug diameters of all cul ti vars increased (17 .8 cm, averaged over all grasses).

K~yugrass density at the end of the experiment (data not shown) was reduced most by sequential treat­ments of quinclorac and MSMA + triclopyr (8.4 and 7.3 stems per 0.1 m2 compared with 203.5 stems per 0.1 m2 in the control plots). MSMA and triclopyr sequential treatments reduced density by 74 and 80% (54.4 and 39.0 stems per 0.1 m2).

184

The results of this research can be integrated into a kikuyugrass management program. Where a cool sea­son species such as perennial ryegrass, tall fescue, or Kentucky bluegrass is in a mixed sward with kikuyugrass, sequential applications of a combination of MSMA and triclopyr can be used to reduce the density and competitiveness of kikuyugrass. This will allow reinvasion of the desired cool season species. Some reseeding of the cool season species may be necessary during the reestablishment process if the ini­tial cool season stand is not adequate or uniform. Where reestablishment of warm season species (com­mon bermudagrass, hybrid bennudagrass, and zoysia) is desired, sequential applications of MSMA may be used. Triclopyr can injure warm season species. Once the desired species is reestablished through sequential her­bicide treatment and reseeding, proper management of that species to keep it competitive together with an occasional herbicide treatment as needed should prevent kikuyugrass reinvasion. Quinclorac would be a desira­ble herbicide for sequential control of kikuyugrass, alone or in appropriate combinations on both cool and warm season turf species, if it becomes registered.

LITERATURE CITED

1. Cudney, D. W., V. A. Gibeault, R. L. Baldwin, and J. R. Breece. 1982. Chemical and cultural control of kikuyugrass in turf. Calif. Agric. 36(1):4-5 .

2. Edwards, D. C. 1937. Three ecotypcs of Pennisetum clandestinum Hochst. (Kikuyugrass). Empire J. Agric. 5:371-377.

3. McMaugh, P. 1971. Control of encroachment of Agrostis spp. swards by warm season turfgrasses. J. Spons Turf Res. Inst. 47 :33--40.

4. Quinlan, T. J., K. A. Shaw, and W.H.R. Edgley. 1975. Kikuyugrass. Queensland Agric. J. Nov.-Dcc.:737-749.

5. White, R. and P. Lovell . 1981. Morphology and spread of kikuyugrass (Pennisetum clandestinum Hochst.). Abstr., XIII Int. Bot. Congr., Syd• ney, Australia. p. 390.

6. Youngner, V. B. 1971. Kikuyugrass-its management and control. Calif. Turfgrass Culture 21(1):1-3.

7. Youngner, V. B. 1961. Observations on the ecology and morphology of Pennisetum clandeslinum. Phyton 16(1):77-84.

8. Youngner, V. B. 1961. Low temperature induced male sterility in male fertile Pennisetum clandestinum. Science 333:577.

9. Youngner, V. B. and J. R. Goodin. 1961. Control of Pennisetum c/andestinum, kikuyugrass. Weeds 19:238-242.

Volume 7, Issue I (January-March) 1993