Efficacy of Preemergence Herbicides in Turfgrasses. B.J. Johnson and T.R. Murphy

Transcription

1 Efficacy of Preemergence Herbicides in Turfgrasses B.J. Johnson and T.R. Murphy Cultural and chemical management practices are needed to maintain a high quality turfgrass. One of these practices is to control weeds that germinate and emerge at various times during the year. McCarty and Colvin (1990) reported that effective weed control begins with proper management practices that encourage a dense, thriving turf. They concluded that a healthy turf shades the soil and prevents sunlight penetration to weed seed and seedlings. Therefore, a thick, dense turf produces competition to emerging seedlings and minimizes the physical space available for weeds to become established. Crabgrass (Digitaria spp.) and goosegrass (Eleusine indica [L.] Gaertn.) are problem summer annual weeds on home lawns, golf courses, athletic fields, parks, and other turfgrass areas. Although proper fertility levels will reduce crabgrass densities (Johnson and Bowyer, 1982; Johnson and Carrow, 1993; Murray et al. 1983), it is still necessary, in most instances, to control weeds with herbicides. Herbicide selection depends on weeds present in the area and the ability of the herbicide to consistently control weeds throughout the growing season. Although preemergence herbicides have activity on crabgrass and goosegrass (Bhowmik and Bingham, 1990; Dernoeden and Davis, 1985; Dernoeden and Krouse, 1991; Johnson and Murphy, 1987; 1989; 1993; Sawyer and Jagschitz, 1987; Watschke et al. 1988; Watschke and Hamilton, 1990; Webster et al. 1986), the selection of the herbicide as well as the rate of application is important for consistent control. Oxadiazon applied at 4.0 lb ai/acre 1 controlled goosegrass better than any other preemergence herbicide (Johnson and Murphy, 1993). However, when oxadiazon rate was reduced to 3.0 lb/acre, goosegrass control was reduced to levels similar to other preemergence herbicides (Johnson and Murphy, 1987, 1989). The performance of preemergence herbicides often depends on the length of the growing season. Preemergence herbicides applied for crabgrass control in Georgia and the southeastern United States must perform effectively for approximately six to seven months. However, the length of the growing season for this weed in the northeast United States is four to five months. Therefore, the efficacy of preemergence herbicides and the application rate in the northeast is often different compared to the southeast. For example, in Georgia, the normal use rate for pendimethalin is 3.0 lb/acre compared to 1.5 lb/acre in the northeast. When pendimethalin was applied to cool-season grasses at 1.5 lb/acre, crabgrass control was >82% in Rhode Island (Sawyer and Jagschitz, 1987), Pennsylvania (Watschke et al., 1988), and Massachusetts (Bhowmik and Bingham, 1990). However, crabgrass control in Georgia when pendimethalin was applied at 3.0 lb/acre to common bermudagrass [Cynodon dactylon (L.) Pers.] varied from 64 to 87% in seven experiments from 1986 through 1991(Johnson and Murphy, 1987, 1989; 1993). Another example in the response between geographical location occurred with dithiopyr. Crabgrass control ranged from >90% in Maryland (Dernoeden and Krouse, 1991) and Pennsylvania (Watschke and Hamilton, 1990), to 51 to 95% in Georgia (Johnson and Murphy, 1989; 1993) with dithiopyr at 0.5 lb/acre. In general, crabgrass control was similar when prodiamine was applied at 0.75 lb/acre in Georgia (75-98%) (Johnson and Murphy, 1989; 1993) and at 0.5 lb/acre in the northeast (80-93%) (Dernoeden and Davis, 1988; Dernoeden and Krouse, 1991; Watschke and Hamilton, 1990). To improve the consistency of weed control with herbicides in Georgia, sequential applications of preemergence and postemergence herbicides were made in an earlier study (Johnson, 1993). In this experiment, large crabgrass [D. Sanguinalis (L.) Scop.] control in common bermudagrass was greater (94%) in plots treated with oxadiazon at 1.0 lb/acre on February 24 and followed by MSMA at 2.0 lb/acre on May 11, 1992, than when either herbicide 1

2 was applied alone at the same respective dates (20 to 60%) (Figure 1). Similar results were observed from sequential applications of pendimethalin at 1.0 lb/acre and MSMA at 2.0 lb/acre (Johnson, 1993). Goosegrass control in common bermudagrass was greater during 1991 (84%) and 1992 (96%) from sequential applications of dithiopyr at 0.38 lb/acre (February 27, 1991 and April 1, 1992) and MSMA plus metribuzin at lb/acre (June 3, 1991 and June 24, 1992) than when either herbicide was applied alone (Johnson, 1993) (Figure 2). There was no advantage from sequential oxadiazon and MSMA plus metribuzin treatments on goosegrass control when oxadiazon was applied at 2.0 lb/acre in 1991 and 4.0 lb/acre in 1992, or when diclofop at 1.0 lb/acre was applied postemergence in June either year. Tank-mixed combinations of preemergence and postemergence herbicides applied to emerged large crabgrass and goosegrass, generally did not provide effective control (Johnson 1994a). An exception occurred in two of three experiments when dithiopyr (0.25 lb/acre) plus MSMA (2.0 lb/acre) was applied mid-may, and controlled large crabgrass better than the herbicides applied alone (Figure 3). Quinclorac effectively controlled large crabgrass and there was no increase in control when tank-mixed with pendimethalin or dithiopyr (Johnson, 1994a). Tankmixture of various preemergence and postemergence herbicides did not control goosegrass as effectively as the same herbicides applied sequentially (Johnson, 1993; 1994a). Herbicides are used extensively in Georgia to control large crabgrass and goosegrass in turfgrasses, and there is a need for preemergence herbicides to be more consistent in weed control throughout the growing season. Therefore, efficacy experiments were conducted to determine the effect of rate, formulation, and application frequency of preemergence herbicide on large crabgrass and goosegrass control and the tolerance of turfgrasses to these herbicides. MATERIAL AND METHODS General information. Herbicides were evaluated from 1991 through 1994 for preemergence large crabgrass and goosegrass control in turfgrasses. The nomenclature ofherbicides and companies furnishing the herbicides are given in table 1. Location of experiments and dates of treatment are shown in table 2. Preemergence herbicides were applied to a Kentucky bluegrass (Poa pratensis L.) at Butternut Creek Golf Course, Blairsville and to common bermudagrass at Cabin Creek Golf Course, Griffin, Beaver Lake Golf and Country Club, Gay, and Georgia Station, Griffin. Weeds were indigenous to each site. Weeds evaluated were large crabgrass and goosegrass at Butternut Creek and Beaver Lake, goosegrass at Cabin Creek, and large crabgrass at the Georgia Station. The soil type was Cecil sandy loam at the Georgia Station, Cabin Creek, and Beaver Lake golf courses, and Hatboro loam at Butternut Creek golf course. Benefin plus oryzalin, benefin plus trifluralin, bensulide plus oxadiazon, butralin, dithiopyr G, oxyfluorfen plus oryzalin, oxadiazon, and oxadiazon plus benefin were formulated as granules and mixed with sand and applied by hand. All other herbicides were applied as a broadcast spray with a CO 2 backpack sprayer using 24 PSI to deliver 40 gal water per acre. 2

3 Table 1. Nomenclature of Herbicides Name Common Tradea Chemical Company Benefin + oryzalin XL benefin = N-butyl-N-ethyl-2,6-dinitro-4- (trifluoromethyl)-benzenamine; oryzalin = 4-(dipropylamino)-3,5- dinitrobenzene-sulonamide DowElanco Benefin +trifluralin Team trifluralin = 2,6 -dinitro-n-n-dipropyl-4- (trifluoro-methyl)benzenamine; benefin given above DowElanco Benefin + oxadiazon Goosegrass/ Crabgrass Control? bensulide = 0,0-bis(1-methyl-oxadiazonethyl) S-[2-[(phenylsulfonyl) amino]ethyl]phosphorodithioate; O.M.Scott oxadiazon = 3-[2,4-dichloro-5- (1- methylethoxy)phenyl]-5-(1,1-dimethylethyl)- 1,3,4-oxadiazol-2-(3H)-one Butralin EXP 30910A EXP31068A 4-(1,1-dimethylethyl)-N-(1methylpropyl)-2,6- dinitrobenzen-amine Rhone-Poulenc Diclofop Illoxan (±)-2-[4-(2,4-dichlorophenoxy) phenoxy]propanoic acid Dithiopyr Dimension S,S-dimethyl 2-(difluoromethyl)-4-(2- methylpropyl)-6-(trifluoro-methyl)-3,5- pyridinedicarbothioate Metribuzin Sencor 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)- 1,2,4-triazin-5(4H)-one Metolachor Pennant 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-1-methylethyl)acetamide AgrEvo Monsanto Rohm & Haas Miles CIBA MSMA Daconate 6 monosodium salt of MAA ISK Biotech Oxyfluorfen + oryzalin Rout oxyfluorfen = 2-chloro-1-(3-ethoxy)- 4- nitrophenoxy)-4-(trifluoromethyl)benzene; oryzalin - given above Grace/Sierra Oryzalin given above DowElanco Oxadiazon Ronstar given above Rhone-Poulenc Oxadiazon + benefin Regalstar given above Regal Pendimethalin PRE-M Turfweed- Grass Control N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenenamine Lesco O.M. Scott Prodiamine Barricade RegalKade N3,N3-di-n-propyl 2,4-dinitro-6-(trifluoromethyl)-m-phenylenediamine Sandoz Regal Quinclorac Drive 3,7-dichloro-8-quinoline-carboxylic acid BASF a. Trade and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment. A given herbicide may have more than one trade name, and the one used is from the company furnishing the herbicide. 3

4 Table 2. Location of Weed Control Studies in Turfgrasses Experiment Turfgrass Location Date applied Preemergence large crabgrass/goosegrass control Kentucky bluegrass Butternut Creek Golf Course, Blairsville, GA 1992: March 2,May 4 Preemergence large crabgrass/goosegrass control Common bermudagrass Cabin Creek Golf Course, Griffin, GA 1992: April 1,May 26 Preemergence large crabgrass control Common bermudagrass Georgia Station Griffin, GA 1991: February 25, April : February 24, April 22 Preemergence goosegrass control Common bermudagrass Beaver LakeGolf and Country Club, Gay, GA 1993: February 22, April 20 Preemergence large crabgrass/goosegrass control Common bermudagrass Beaver Lake Golf and Country Club, Gay, GA 1994: February 21, April 20 Actively-growing Kentucky bluegrass on fairways at the Butternut Creek Golf Course was mowed weekly with a reel mower to a height of approximately 1½ inches. The turfgrass was not fertilized or irrigated. However, rainfall distribution was favorable with total rainfall from March through August of 34 inches. Actively-growing common bermudagrass on fairways at Cabin Creek and Beaver Lake were mowed weekly with a reel mower to a height of approximately 3/4 to 1-inch. Common bermudagrass at the Georgia Station was mowed three times per week at ¾-inch. Turfgrass clippings were returned to the sod at all locations. Turfgrasses at Cabin Creek and Georgia Station were irrigated as needed to maintain optimum growth, while turfgrass at Beaver Lake was not irrigated. Turfgrass at Beaver Lake in 1993 received only 4.2-inches of rainfall from mid-may until early August and severe drought stress occurred for two to three-week periods during June and again during July. By mid- to late August, the turfgrass was actively growing. Rainfall at Beaver Lake during 1994 was above normal with 32 inches. All common bermudagrass was fertilized with 10 lb/1000 ft 2 of in April, with additional N from ammonium nitrate at 1.0 lb/1000 ft 2 applied late May and July at Cabin Creek and Georgia Station. Herbicides at rates given in tables 3 through 5 were applied for large crabgrass and goosegrass control in Kentucky bluegrass at Butternut Creek Golf Course, Blairsville, during Herbicides applied for large crabgrass control in common bermudagrass at the Georgia Station are given in table 6 during 1991 and 1992, and at Beaver Lake Golf and Country Club, Gay are given in tables 7 through 9 during Herbicides applied for goosegrass control in common bermudagrass at Cabin Creek Golf Course, Griffin are given in tables 11 through 12 during 1992, at Beaver Lake Golf and Country Club, Gay in tables 13 through 15 during 1993, and tables 7 through 9 during With the exception of Cabin Creek location in 1992, 4

5 herbicides were applied initially on February 25 ± 4 days. At Cabin Creek, herbicides were applied on April 1. When a second application was made, it was applied approximately eight weeks later (table 2). Table 3. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Kentucky Bluegrass. Butternut Creek Golf Course, Blairsville, GA Treatments a Turfgrass quality b Large crabgrass control c Goosegrass control c Herbicide Formulation Rate Jun 22 Aug 31 Jun 22 Aug 31 Aug 31 lb/ac 1 to 10 % % Untreated Bensulide+ oxadiazon G * * * * Oxadiazon + benefin carrier * * Metolachlor 7.8 EC * Pendimethalin + metolachlor 60 WDG EC * Pendimethalin 60 WDG * * Pendimethalin carrier * Oryzalin 4AS * Benefin + trifluralin Benefin + oryzalin G * * G * * Prodiamine 65 WDG * LSD (0.05) NS NS a. Herbicides were initially applied on March 2, 1992; an asterisk indicates that a second application was made on May 4. Bensulide plus oxadiazon, oxadiazon plus benefin, benefin plus trifluralin, and benefin plus oryzalin were 5

6 applied as single products. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Large crabgrass and goosegrass control ratings were based on 0 = no control and 100 = complete control. Table 4. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Kentucky Bluegrass. Butternut Creek Golf Course, Blairsville, GA Treatments a Turfgrasss quality b Large crabgrass control c Goosegrass control c HERBICIDE FORMULATION RATE JUN 22 AUG 31 AUG 31 AUG 31 lb/acre 1 to % Untreated Butralin 5 G * Benefin 2.5 G Oxyfluorfen + oryzalin G * Pendimethalin 1.71 G Oxadiazon + dithiopyr G LSD (0.05) 1.4 NS a. Herbicides were initially applied on March 2, 1992; an asterisk indicates that a second application was made on May 4. Oxyfluorfen plus oryzalin were applied as a single product b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Large crabgrass and goosegrass control ratings were based on 0 = no control and 100 = complete control. 6

7 Table 5. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Kentucky Bluegrass. Butternut Creek Golf Course, Blairsville, GA Treatments a Turfgrasss quality b Large crabgrass control c Goosegrass control c HERBICIDE FORMULATION RATE JUN 22 AUG 31 AUG 31 AUG 31 lb/acre 1 to % Untreated Dithiopyr 1 EC * Dithiopyr 0.25 G Pendimethalin 60 WDG Oxadiazon 2 G Dithiopyr carrier * * LSD (0.05) NS NS 8 22 a. Herbicides were initially applied on March 2, 1992; an asterisk indicates that a second application was made on May 4. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Large crabgrass and goosegrass control ratings were based on 0 = no control and 100 = complete control. Weed control and turfgrass quality ratings were visually estimated at various times during the growing season. Weed control ratings were made in July and late August and based on 0 to 100 where 0 = no control, <80% unacceptable, and 100 = complete control. Turfgrass quality ratings were made initially in April and at monthly intervals through August, and based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense stand. Herbicide treatments in all experiments were arranged in a randomized complete block design with four replications. Plot size was 5' by 10'. Data were analyzed statistically using the General Linear Models Procedure (SAS Institute, 1982). Means were separated by LSD at P = Data in experiment at the Georgia Station are presented as an average from two years. The data from golf course experiments are reported for each year due to treatment by year interactions 7

8 RESULTS AND DISCUSSION Large crabgrass control. The control of large crabgrass in Kentucky bluegrass at Butternut Creek golf course with all herbicides was >70% throughout the spring and summer in 1992 (tables 3, 4, and 5). Single applications of bensulide plus oxadiazon at lb/acre, butralin at 5.0 lb/acre, oxadiazon plus dithiopyr at lb/acre, two applications of pendimethalin at 1.5 lb/acre, and benefin plus oryzalin at lb/acre were the only herbicides that controlled less than 80% large crabgrass by late August. Bensulide plus oxadiazon applied initially at lb/acre, and followed by lb/acre or when lb/acre was applied twice controlled a higher percentage of large crabgrass (88%) than when applied once at lb/acre (70%). Sequential herbicide applications did not always improve large crabgrass control in Kentucky bluegrass. Pendimethalin applied at 1.5 lb/acre on March 2 and on May 4 did not control large crabgrass as effectively (71%) as when 3.0 lb/acre was applied in March (88%) (table 3). The poorer control was probably related to large crabgrass germination in plots treated at the reduced rate before the second pendimethalin application was made. In some instances, there was no difference in large crabgrass control in Kentucky bluegrass whether the preemergence herbicides were applied as a single or split application, providing the total rate for the year was applied at the recommended level. Examples were oxyfluorfen plus oryzalin applied once at lb/acre, compared with two applications at lb/acre (table 4) and dithiopyr EC applied once at 0.5 lb/acre compared with two applications at 0.25 lb/acre (table 5). Effective large crabgrass control in Kentucky bluegrass turf was obtained with single applications of oxadiazon plus benefin, pendimethalin, prodiamine, dithiopyr, and oxyfluorfen plus oryzalin, while two applications were needed with bensulide plus oxadiazon, benefin plus trifluralin, and benefin plus oryzalin. Effective control of large crabgrass in Kentucky bluegrass with oryzalin, benefin plus oryzalin and benefin plus trifluralin differs from those reported (29 to 49%) at the same location in an earlier study (Johnson and Murphy, 1993). The difference in herbicide performance may be related in part to rainfall and/or competition from a higher large crabgrass density in the earlier study. Pendimethalin and oxadiazon applied in one or two applications provided good to excellent large crabgrass control in common bermudagrass in late August (6 months after the initial application) at the Georgia Station (table 6). Large crabgrass control with pendimethalin was similar whether applied once at 3.0 lb/acre (96%) or twice at 1.0 lb/acre (90%). However, there were differences in large crabgrass control from sequential oxadiazon applications. The control was 97% when oxadiazon was applied once at 4.0 lb/acre, but <84% when oxadiazon was applied sequentially at 0.75 lb/acre initially, and followed by <1.0 lb/acre eight weeks later (<84%). When the initial oxadiazon application was 1.0 lb/acre and followed by 0.75 lb/acre, large crabgrass control was consistently greater (92%), compared to an initial application of 0.75 lb/acre, followed by 1.0 lb/acre (84%). There was no difference in control when 1.0 lb/acre was followed by 0.75 lb/acre, compared to one application at 4.0 lb/acre rate. To obtain consistent large crabgrass control with oxadiazon in common bermudagrass at the lowest total rate, it was necessary to apply 1.0 lb/acre as the initial treatment and follow with 0.75 lb/acre. When 0.75 lb/acre was applied initially, the rate for the second application needed to be increased to 1.5 lb/acre to maintain >90% control. There was no increase in control when the initial application was > 1.0 lb/acre regardless of the rate of the second application. In the southern United States, the recommended rates for large crabgrass control with pendimethalin and oxadiazon are 3.0 lb/acre and 3.0 to 4.0 lb/acre, respectively. However, when common bermudagrass is properly maintained, effective large crabgrass control can be obtained with reduced rates for pendimethalin ( lb/acre) and oxadiazon ( lb/acre). All preemergence herbicides controlled >90% large crabgrass in common bermudagrass at six months after the initial treatment at Beaver Lake Golf & Country Club during 1994 with the exception of butralin (tables 7, 8, and 9). The control with butralin was 79%. Sequential applications did not improve large crabgrass control. One application of bensulide plus oxadiazon, oxyfluorfen plus oryzalin, pendimethalin, dithiopyr, prodiamine, oxadiazon plus benefin, 8

9 oryzalin, and benefin plus oryzalin effectively controlled large crabgrass, compared to sequential applications. 9

10 Table 6. Influence of Sequential Preemergence Herbicide Treatments on Large Crabgrass spp. Control in Common Bermudagrass, Griffin, GA. Average 1991 and Treatments a Turfgrasss quality b Large crabgrass control c HERBICIDE RATE JUN 22 AUG 25 AUG 25 lb/acre 1 to % Untreated Pendimethalin * * * * Oxadiazon * * * * * * * * * * LSD (0.05) a. Herbicides were initially applied February 24, an asterisk indicates that a second application was made April 22 ± 1 day during 1991 and b. Turfgrass quality ratings are averages from two years and based on 1 = turf brown and 10 = dark green with uniform turfgrass cover. c. Large crabgrass control ratings are averages from two years and based on 0 = no control and 100 = complete control. 10

11 11

12 Table 7. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, Ga Treatments a Turfgrass quality b Large crab grass control c Goose grass control c HERBICIDE FORMULATION RATE APR 4 APR 20 MAY 23 AUG 26 AUG 26 ib/acre 1 to 10 (%) Untreated Oryzalin 4AS Ronstar 2G Pendimethalin 60 WDG * carrier * % Dithiopyr 1 EC * * G * * * * Prodiamine carrier % * LSD (0.05) NS

13 a. Herbicides were initially applied on February 21, 1994; an asterisk indicates that a second application was made April 20. b. Turfgrass quality ratings were based on 1 to 10 were 1 = turf brown on dead and 10 = dark green with uniform dense turf. c. Large crabgrass and goosegrass control ratings were based on 0 = no control and 100 = complete control. 13

14 Table 8. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA Treatments a Turfgrasss quality b Large crabgrass control c Goose grass control c HERBICIDE FORMULATION RATE APR 4 APR 20 MAY 23 AUG 26 AUG 26 lb/acre 1 to % Untreated Oxadiazon 2 G Oxadiazon + benefin carrier * * Oxyfluorfen + oryzalin G * * Bensulid + oxadiazon G * * * LSD (0.05) NS a. Herbicides were initially applied on February 21, 1994; an asterisk indicates that a second appli-cations was made April 20. Oxadiazon plus benefin, oxyfluorfen plus oryzalin and bensulide plus oxa-diazon were applied as single products. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Large crabgrass and goosegrass control ratings were based on 0 = no control and 100 = complete control. 14

15 Table 9. Influence of Preemergence Herbicides on Large Crabgrass and Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA 1994 Treatments a Turfgrasss quality b Large crabgrass control c Goose grass control c HERBICIDE FORMULATION RATE APR 4 APR 20 MAY 23 AUG 26 AUG 26 lb/acre 1 to 10 % Untreated Benefin + oryzalin G Benefin + trifluralin G * * Butralin 5 G LSD (0.05) NS a. Herbicides were initially applied on February 21, 1994; an asterisk indicates that a second applications was made April 20. Benefin plus oryzalin and benefin plus trifluralin were applied as single products. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Large crabgrass and goosegrass control ratings were based on 0 = no control and 100 = complete control. Goosegrass control. Goosegrass control from preemergence herbicides was not as good as it was for large crabgrass in Kentucky bluegrass at Butternut Creek Golf Course in 1992 (tables 3, 4, and 5). For example, 37 herbicide treatments were applied at various rates during this period and goosegrass control was >80% in only 12 of these treatments. Sequential applications of herbicides were needed for effective goosegrass control. Bensulide plus oxadiazon applied at lb/acre provided 39% goosegrass control at six months after the initial application (table 3). The control was improved to >86% when this herbicide combination was applied initially at lb/acre and followed by lb/acre eight weeks later, or when lb/acre was applied twice. Goosegrass control was better in plots treated twice with pendimethalin WDG ( lb/acre) (96%) and prodiamine ( lb/acre) (86%) than pendimethalin at 3.0 lb/acre (43%) and prodiamine at 0.75 lb/acre (64%) applied alone. Dithiopyr at 0.5 lb/acre controlled goosegrass (>80%) in Kentucky bluegrass regardless of formulation (table 5). However, when dithiopyr was applied on a fertilizer carrier at 0.25 lb/acre, and followed eight weeks later with >0.125 lb/acre, goosegrass control was better than when this formulation was applied once at 0.38 lb/acre. Oxyfluorfen plus oryzalin did not effectively control goosegrass in Kentucky bluegrass except when applied at the highest rate ( lb/acre) (table 4). The control was better in plots treated once at lb/acre (96%) than lb/acre applied twice (70%). Therefore, it was necessary to apply an initial rate of oxyfluorfen plus oryzalin rate greater than lb/acre to maintain the desired goosegrass control level throughout the spring and summer. 15

16 Goosegrass control was acceptable in Kentucky bluegrass when benefin plus oryzalin was applied twice at lb/acre (89%), while the control was unacceptable when oryzalin was applied twice at 1.5 lb/acre (54%) (table 3). Oxadiazon at 4.0 lb/acre did not adequately control goosegrass (64%) (table 5). In an earlier study at the same location, goosegrass control was 82 to 83% at the same rate (Johnson and Murphy, 1993). Pendimethalin WDG and prodiamine effectively controlled goosegrass (>84%) at Cabin Creek in (table 10). The control with pendimethalin WDG was similar whether 3.0 lb/acre was applied once or 1.5 lb/acre applied twice. Pendimethalin on fertilizer carrier applied twice at 1.5 lb/acre provided 70% goosegrass control. There was no advantage in goosegrass control when prodiamine was applied once at 0.75 lb/acre or 0.75 lb/acre followed by 0.25 lb/acre eight weeks later. Both provided > 84% goosegrass control. Two applications of oxadiazon plus benefin controlled goosegrass better (76%) in common bermudagrass at Cabin Creek Golf Course in 1992 than the combination applied once (56%) (table 10). Control was 75% when benefin plus oryzalin were applied twice at lb/acre. Goosegrass control with bensulide plus oxadiazon applied initially at lb/acre, and followed by lb/acre was greater than control from the same herbicides applied twice at lb/acre. 16

17 Table 10. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass.Cabin Creek Golf Course, Griffin, Ga Treatments a Turfgrass quality b Goosegrass Herbicide Formulation Rate May 26 Aug 25 Aug 26 lb/acre to % Untreated Bensulide + oxadiazon G * * * * Oxadiazon benefin carrier * * Metolachlor 7.8 EC * Pendimethalin + metolachlor 60 WDG EC * Pendimethalin 60 WDG * * Pendimethalin carrier *

18 Treatments a Turfgrass quality b Goosegrass Herbicide Formulation Rate May 26 Aug 25 Aug 26 lb/acre to % Benefin + trifluralin C * * Benefin + oryzalin G * * Prodiamine 65 WDG * LSD (0.05) NS a. Herbicides were initially applied on April 1, 1992; an asterisk indicates that a second application was made on May 26. Bensulide plus oxadiazon, oxadiazon plus benefin, benefin plus trifluralin, and benefin plus oryzalin were applied as single products. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Goosegrass control ratings were based on 0 = no control and 100 = complete control. Goosegrass control in common bermudagrass with butralin applied at 6.0 lb/acre (94%) was greater in 1992 than when applied at 5.0 lb/acre (59%), or when applied at 3.0 lb/acre, and followed by 2.0 lb/acre (57%) (table 11). Oxadiazon, dithiopyr, and combinations of dithiopyr with oryzalin, pendimethalin, or oxadiazon effectively controlled goosegrass in 1992 (table 12). Dithiopyr EC and dithiopyr fertilizer carrier formulations applied at 0.38 lb/acre also effectively controlled goosegrass. These results show that a single application of pendimethalin, prodiamine, oxadiazon, dithiopyr, butralin, and oxyfluorfen plus oryzalin effectively controlled goosegrass during Goosegrass control in common bermudagrass at Beaver Lake Golf and Country Club varied with preemergence herbicides at six months after the initial treatment in 1993 (tables 13, 14, and 15). Oxadiazon and pendimethalin consistently controlled >80% goosegrass. However, goosegrass control in most instances was not as good in 1993 when treated with prodiamine, dithiopyr, oxadiazon plus benefin, and oxyfluorfen plus oryzalin as they did at Cabin Creek location in 1992 (tables 10, 11, and 12). The test areas in 1992 were irrigated as needed to maintain optimum turfgrass growth while the areas in 1993 were not irrigated. During May through July 1993, only 7-inches of rainfall occurred. This was 10-inches below normal. Therefore, drought stress likely influenced the 1993 results. 18

19 Table 11. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Cabin Creek Golf Course, Griffin, GA Treatments a Turfgrass quality b to Goosegrass control c % Herbicide Formulation Rate lb/acre May 26 Aug 26 Aug 26 Untreated Oxadiazon 2 G Butralin 5 G * Benefin 2.5 G Oxyfluorfen + oryzalin G * * * * Pendimethalin 1.71 G Oxadiazon + dithiopyr G LSD (0.05) NS a. Herbicides were initially applied on April 1, 1992; an asterisk indicates that a second application was made on May 26. Oxyfluorfen plus oryzalin were applied as a single product. 19

20 b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Goosegrass control ratings were based on 0 = no control and 100 = complete control. Table 12. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Cabin Creek Golf Course, Griffin, GA Treatments a Turfgrass quality b Goosegrass control c Herbicide Formulation Rate May 26 Aug 25 Aug 26 lb/acre to % Untreated Oxadiazon 2 G Dithiopyr 1 EC * Dithiopyr+ oryzalin 1 EC + 4 AS Dithiopyr + pendimethalin 1 EC + 60 WDG Dithiopyr + oxadiazon 0.25 G + 2 G Dithiopyr carrier * * LSD (0.05) NS NS 18 a. Herbicides were initially applied on April 1, 1992; an asterisk indicates that a second application was made on May 26. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Goosegrass control ratings were based on 0 = no control and 100 = complete control. 20

21 Table 13. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA Turfgrass quality b 1 to 10 Goosegrass control c % Herbicide Formulation Rate lb/acre May 10 June 17 Aug 18 July 28 Aug 18 Untreated Butralin 5 G Ronstar 2 G Bensulide+ oxadiazon G *+ 0.75* * * Pendimethalin 60 WDG * * Oxyflourfen + oryzalin G * + 0.5* * + 1.5* LSD (0.05) NS 2.1 NS a. Herbicides were initially applied on February 22; an asterisk indicates that a second application was made on April 20, Bensulide plus oxadiazon and oxyfluorfen plus oryzalin were applied as single products. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Goosegrass control ratings were based on 0 = no control and 100 = complete control. 21

22 Table 14. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA Treatments a Turfgrass quality b Goosegrass control c Herbicide Formulation Rate May 10 June 17 Aug 18 July 28 Aug 18 lb/acre to % Untreated Oxadiazon benefin carrier * * Prodiamine 65 WDG * * Prodiamine carrier * * LSD (0.05) 1.4 NS a. Herbicides were initially applied on February 22; an asterisk indicates that a second application was made on April 20, Oxadiazon plus benefin was applied as a single product. b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Goosegrass control ratings were based on 0 = no control and 100 = complete control. 22

23 Table 15. Influence of Preemergence Herbicides on Goosegrass Control in Common Bermudagrass. Beaver Lake Golf and Country Club, Gay, GA Treatments a Turfgrass quality b Goosegrass control c Herbicide Formulation Rate May 10 Aug 18 July 28 Aug 18 lb/acre to % Untreated Dithiopyr 1 EC * * Dithiopyr + oxadiazon 0.25 G + 2 G Oxadiazon 2 G Prodiamine 65 WDG LSD (0.05) NS NS a. Herbicides were initially applied on February 22; an asterisk indicates that a second application was made on April 20, b. Turfgrass quality ratings were based on 1 to 10 where 1 = turf brown or dead and 10 = dark green with uniform dense turf. c. Goosegrass control ratings were based on 0 = no control and 100 = complete control. 23

24 Oxyfluorfen plus oryzalin applied twice at lb/acre in common bermudagrass controlled 95% goosegrass in 1993 (table 13). Goosegrass control from oxyfluorfen plus oryzalin at < lb/acre was not acceptable. Prodiamine WDG at 0.75 lb/acre controlled goosegrass 27% in common bermudagrass during 1993 (table 14). The control was improved to 85% when prodiamine was applied at 0.75 lb/acre, and followed with 0.5 lb/acre eight weeks later. Prodiamine applied on a fertilizer carrier in 1993 did not control goosegrass effectively (<38%) regardless of number of applications. To maintain >80% goosegrass control in common bermudagrass during 1993 with the dithiopyr EC, it was necessary to apply 0.75 lb/acre once, or 0.25 lb/acre twice (table 15). The control was unacceptable when one application was made at 0.5 lb/acre. Combinations of dithiopyr G at 0.38 lb/acre plus oxadiazon at 2.0 lb/acre controlled goosegrass 80%. Goosegrass control during the drought stress year of 1993 was better with oxadiazon and pendimethalin during drought stress than from other preemergence herbicides. Although oxadiazon plus benefin does not always control goosegrass as effectively as oxadiazon or pendimethalin (table 10), it was effective during the 1993 drought period when applied sequentially (table 13). Higher rates were required for oxyfluorfen plus oryzalin, prodiamine, and dithiopyr to maintain an acceptable goosegrass control level during drought stress, compared to irrigation areas. Dithiopyr EC applied twice at 0.38 lb/acre was the only herbicide that controlled 90% goosegrass in common bermudagrass at Beaver Lake Golf and Country Club during 1994 (tables 7, 8, and 9). The control was 83 to 84% in plots treated once with oxyfluorfen plus oryzalin at lb/acre and twice with oryzalin at 1.5 lb/acre, dithiopyr EC at 0.25 lb/acre, and benefin plus oryzalin at lb/acre. Goosegrass control was 70 to 79% in plots treated once with oxadiazon at 3.0 lb/acre, benefin plus oryzalin at lb/acre, oxyfluorfen plus oryzalin at lb/acre, twice with dithiopyr at 0.25 lb/acre, and prodiamine at 0.75 lb/acre, followed by 0.38 lb/acre. During this period, goosegrass control was <70% when treated with prodiamine applied as a fertilizer carrier formulation, and with butralin, oxadiazon plus benefin, bensulide plus oxadiazon and benefin plus trifloralin. Dithiopyr and prodiamine are the most recently registered preemergence herbicide for use in turfgrasses. Dithiopyr EC applied twice at 0.25 lb/acre consistently controlled large crabgrass and goosegrass better than 0.5 lb/acre applied once. Control from sequential dithiopyr applications averaged 94% for large crabgrass and 79% for goosegrass, and is similar to that reported in an earlier study (Johnson and Murphy, 1993). These results indicate that a single application of prodiamine at 0.75 lb/acre is sufficient for large crabgrass control, but split applications are needed for consistent goosegrass control. Turfgrass response. Kentucky bluegrass. Oxyfluorfen plus oryzalin applied once at lb/acre of twice at lb/acre were the only herbicides that significantly reduced Kentucky bluegrass quality when ratings were made in June (table 4). Although the difference was not significant, Kentucky bluegrass quality was reduced in June when treated twice with oryzalin at 1.5 lb/acre (table 3). In an earlier study (Johnson and Murphy, 1993), oryzalin applied at 2.0 lb/acre significantly reduced the quality of Kentucky bluegrass at four weeks after treatment. The lack of significance in the present study may be related to the presence of white clover (Trifolium repens L.) in the test area. White clover competed with Kentucky bluegrass, resulting in a lower quality turfgrass. No herbicide affected Kentucky bluegrass by late August (tables 3, 4, and 5). Common bermudagrass. Preemergence herbicides applied to bermudagrass in late winter for summer weed control may influence turfgrass quality for several weeks during spring green-up. Due to climatic effects, a herbicide effects on turfgrass quality may vary among years. None of the herbicides evaluated reduced quality of common bermudagrass when compared with untreated turf in May 1991 and 1992 (tables 6, 10, 11, and 12). Similar results were noted in 1993, with the exception of prodiamine (tables 13, 14, and 15). The quality of turf treated with prodiamine was lower than untreated turf, regardless of whether treated with the prodiamine WDG or on a fertilizer carrier. However, reduction in quality was temporary and the turfgrass recovered by mid-june. 24

25 The spring transition of common bermudagrass was three to four weeks earlier in 1994 than previous years. This resulted in a shorter time period from time of herbicide treatment (late February) until transition, allowing several herbicides to reduce turfgrass quality during April (tables 7, 8, and 9). The herbicides that delayed transition in April were oryzalin, pendimethalin, dithiopyr, oxyfluorfen plus oryzalin, benefin plus oryzalin, and benefin plus trifluralin. Common bermudagrass treated with oryzalin at 1.5 to 2.0 lb/acre on February 21 recovered by April 20, while turf treated at 3.0 lb/acre did not recover until May 23 (table 7). The quality of turf treated with pendimethalin WDG at 3.0 lb/acre was lower than untreated turf in April, but recovered fully by late May. Turf treated initially with pendimethalin WDG at 1.5 lb/acre or with the fertilizer carrier at any rate was not affected during April. Both dithiopyr formulations delayed the transition of common bermudagrass when rated on April 4. Turfgrass treated with the dithiopyr EC recovered by April 20; whereas, turf treated with the dithiopyr G did not recover until May 23. Oxyfluorfen plus oryzalin applied at lb/acre did not delay the transition of common bermudagrass (table 8). However, when the initial rate was increased to lb/acre, turf quality was lower on April 4, but recovered by April 20. When lb/acre was applied once in February, the turf did not recover until May 23. Combinations of benefin plus trifluralin delayed the spring transition of common bermudagrass in April, but recovered by May 23 (table 9). Similar results occurred from combinations of benefin plus oryzalin applied at lb/acre. When benefin plus oryzalin was applied initially at < lb/acre, common bermudagrass was not affected until April 20. However, regardless of rate, the turf recovered fully by May 23. In most instances, when injury from preemergence herbicides occurred, common bermudagrass completely recovered by mid- to late May. As reported during 1994, turf injury may occur more frequently when common bermudagrass greens up earlier in the spring. It is likely that less turfgrass injury from preemergence herbicide may be noted in weedy test sites, when compared to weed-free test sites. This can be related to: a) weedy turfgrass sites are usually maintained at lower fertility levels, which results in poorer quality turf and turfgrass injury is not readily detected; b) competition from weeds growing in plots will mask turfgrass injury from herbicides; and c) the poor quality turfgrass may recover before the injury can be detected. Therefore, when herbicides are evaluated for weed control on a weedy turfgrass site, they should also be evaluated on a high quality weed-free turf. Turfgrass tolerance from selected herbicide treatments has been reported (Johnson and Burns, 1985; Johnson, 1994b), while others will be continued and reported when completed. SUMMARY Preemergence herbicides were applied to turfgrasses for evaluation of large crabgrass and goosegrass in Kentucky bluegrass and common bermudagrass in Georgia during 1991 through The major results are as follows (table 16): 1)Preemergence herbicides controlled large crabgrass consistently better than goosegrass. 2) When herbicides were averaged across years and locations for the four year period, large crabgrass control was >90% when treated twice with dithiopyr at 0.25 lb/acre, oryzalin applied twice at 1.5 lb/acre, oxadiazon plus benefin applied once at lb/acre, oxyfluorfen plus oryzalin applied once at lb/acre, pendimethalin applied once at 3.0 lb/acre, and prodiamine applied once at 0.75 lb/acre. Large crabgrass control was 80 to 87% when bensulide plus oxadiazon was applied once at lb/acre, benefin plus oryzalin was applied twice at

26 lb/acre, and benefin plus trifluralin was applied twice at lb/acre. 3) When herbicides were averaged across years and locations for the four year period, goosegrass control >90% was obtained only when treated once with oxyfluorfen plus oryzalin at lb/acre and pendimethalin WDG applied initially at 3.0 lb/acre and followed by 1.5 lb/acre. Goosegrass control ranged from 80 to 84% when treated once with oxadiazon at 3.0 or 4.0 lb/acre, and when treated twice with benefin plus oryzalin at lb/acre, dithiopyr at 0.25 lb/acre on a fertilizer carrier, oxyfluorfen plus oryzalin applied at lb/acre, pendimethalin applied at 1.5 lb/acre on a fertilizer carrier. Dithiopyr EC applied twice at 0.25 lb/acre controlled 79% goosegrass. 4) The quality of Kentucky bluegrass and common bermudagrass turf was generally not affected by preemergence herbicides when ratings were made in late May. Several preemergence herbicides delayed green-up of common bermudagrass in April 1994 when common bermudagrass greened-up three to four weeks early. 1 All herbicide rates are presented as pounds active ingredient per acre. Table 16. Summary of Herbicides Applied for Large Crabgrass and Goosegrass Control in Turfgrasses During 1991 through 1994 in Georgia. Treatments a Percent weed control b Herbicide Rates Large crabgrass Goosegrass lb/acre Benefin + oryzalin 0.75 * * Benefin trifluralin * Bensulide oxadiazon * Butralin 5.0/ Dithiopyr 0.38/ (EC) * Dithiopyr fertilizer carrier * Oryzalin *

27 Oxadiazon 3.0/ Oxadiazon benefin Oxyfluorfen * * oryzalin * * Pendimethalin (WDG) * * Pendimethalin (G) Pendimethalin fertilizer carrier * Prodiamine * /0.38 * a. An asterisk indicates a second herbicide application was made. b. The number of experiments were not the same for all herbicides and weed species. Acknowledgments The authors thank the management of the Butternut Creek Golf Course, Blairsville; Ralph and Randy Dougherty, Cabin Creek Golf Course, Griffin; J. C. Patel, Beaver Lake Golf and Country Club, Gay, Georgia for their cooperation. The authors also gratefully acknowledge the technical assistance of W. Olson, T. Dinkins, and C. Jones. References Bhowmik, P.C. and S.W. Bingham Preemergence activity of dinitroaniline herbicides used for weed control incool-season turfgrasses. Weed Technol. 4: Dernoeden, P.H. and D.B. Davis Smooth crabgrass control with pre- and postemergence herbicides, Proc. Northeast. Weed Sci. Soc. 42: