RP EXP31130A herbicide was applied on August 3 and September 4, 1995, on perennial ryegrass turf which was infested with uniform amounts of bermudagrass. Two rates were applied, 0.18 and 0.36 lb. AI/A, as single or tandem (sequential) applications. EXP31130A caused leaf bleaching (chlorophyll loss) visible at 5DAT, which was also rate dependent and showed maximum expression at 10-14 days after treatment. The bermudagrass did recover somewhat by 24 days after the first treatment. Regrowth of the turf was weak in color, but it did eventually recover. Sequential applications having at least one rate at 0.36 lb. AI/A, caused the greatest changes in color, but not necessarily for leaf bleaching. Based on re-greening of treated bermudagrass after leaf bleaching, decreased time intervals appear warranted. Bermudagrass suppression was achieved from two treatments during the late summer of 1995. Suppression ranged from 12% to 42% based on rates. No damage was visually realized on the host ryegrass turf. Final determination of potential latent necrotic bermuda can be determined during the spring of 1996. The apparent selectivity between ryegrass and bermudagrass may be beneficial for golf course managers.
 

Bermudagrass (Cynodon spp.) is the most widely used species as a southern turfgrass. Due to its tolerance to relatively close mowing, good heat and drought tolerance, and vegetative reproductive capacity (both rhizomes and stolons), it can and has become a "weed" where unwanted. Non-selective control requires re-establishment of the desirable turf species (partial or full renovation).

Non-selective control with mixtures of plant growth regulators and herbicide combinations are practiced, but do not always give satisfactory control or suppression, and tolerance of the cool season host turf is highly rate and application time specific. In addition, tolerance of the desirable cool season host grass itself often occurs within a narrow rate range.

A test was conducted at the University of Arizona to assess the response of bermudagrass to single and sequential rate applications of RP EXP31130A herbicide in a perennial ryegrass turf.

A field test was devised and conducted to assess the response of bermudagrass as a weed in a mowed perennial ryegrass turf, using RP EXP31130A herbicide as a control/suppression agent. The perennial ryegrass "host turf" was a four year old stand of "Palmer" turf-type perennial ryegrass. The ryegrass is maintained as a year round turf and received mowing 2-3 times weekly at 2.5 inches when the turf reached 3.0 inches. The turf is irrigated to avoid moisture stress, receiving 85-90% of the AZMET reference ETo (atmospheric demand for water vapor). The soil at the test site is a Gila fine-sandy loam, with a pH of 7.8. On June 28, 1995, six week old clones of 'Midiron' bermudagrass were transplanted from 4"x4"x3" plastic pots (same field soil) into the perennial ryegrass field plots. Plot size was 5'x 6', with two bermudagrass plugs/plot transplanted 20 inches apart in the center of each plot. Plugs were fertilized 3x week for four weeks with a 500 ppm. solution of Peters 20-20-20 fertilizer to enhance a rapid establishment. Plugs were soil bound (knit) in seven days. The bermuda and perennial ryegrass turf received regular mowing as described above. All clippings were removed with each mowing event.

The perennial ryegrass turf previously received 2.0 lbs. of -N-/1000 ft² from January to April 1995, and a total of 4 ounces of Ferromec/1000 ft² and 0.25 lbs. -N-/1000 ft² during the summer test period.

The application treatments of RP EXP31130A were as follows in lbs. AI/A.

(1) 0.18 + 0; (2) 0.18 + 0.18; (3) 0.18 + 0.36; (4) 0.36 + 0; (5) 0.36 + 0.18; (6) 0.36 + 0.36; with the additional treatments of (7) 1.13 of PROGRASS (ethofumosate); and (8) control.

Treatments were initially applied on August 3, 1995, and again on September 4, 1995 using a CO₂ back-pack sprayer and a three nozzle boom spray at a five foot width using 8004 nozzles, 25 psi, at a final solution delivery rate of 51 gallons per acre. All applications were made before mid-day and irrigated in 12-16 hours afterwards. Experimental design was a RCBD with four replications of each treatment.

Bermudagrass plugs were measured for surface area one day before treatments were applied, and at the end of the season when checks were becoming fall dormant at the last week in November, 1995. Plug size area was determined in cm² to assess changes in growth/control/suppression from treatments. Percent control was determined as a function of change in bermuda plug area. Performance response of the perennial ryegrass was assessed on three occasions, while bermudagrass response was measured (per plug basis) for percent plug bleaching (0-100%), and turfgrass color (1-9, 1=straw, 9=dark green).

August 12 (9DAT/1)

Ryegrass turf was evaluated for overall turfgrass color. Individual plot scores ranged from 5.0 to 8.0 and treatment means ranged from 6.5 to 7.5. Treatments had no effect on ryegrass color (Table 1).

The treatment effect for bleaching scores for bermudagrass was highly significant (P=0.001) at 9DAT. Among treated plots, the percent bleaching on a plug basis (0-100%) ranged from 0% (PROGRASS) to 38%, with a positive linear response with application rate for EXP31130A (Table 2). Mean bleaching scores for 0.18 lb. and 0.36 lb. initial treatments was 33% and 13.1%, respectively. Bleaching occurred at the youngest leaves on the youngest portion of the stolons. This occurred on the youngest 2-3 leaves, followed by the same occurrence on the next youngest phytomere set on the same intact stolon, which progressed "backwards" accordingly.

August 19 (15DAT/1)

Bleaching scores for bermuda were again highly significant (P=0.001), and mean bleaching scores ranged from 0% (PROGRASS) to 23%. Mean bleaching scores for the 0.18 lb. and 0.36 lb. initial treatments were now 8% and 20%, respectively. Note that the bleaching was less at 15DAT/1, than at 9DAT/1, as recovery was occurring (Table 2).

August 29 (25DAT/1)

Percent plug bleaching was non-significant at 25DAT/1, as scores ranged from 3% to 8% bleaching. The bleaching effect was essentially gone at 25DAT/1. Initial EXP31130A treatments at 0.18 lb. and 0.36 lb. rates were averaging 7% and 5% bleaching, respectively, at this time (Table 2).

Mean color scores for bermudagrass plugs were non-significant as well. Mean color scores for all herbicide treated plots ranged from 4.3 to 5.9. The control plot mean color score was 6.5 (not shown) (Table 3).

The second application treatments (sequential rates) were applied on September 4, 1995.

September 9 (5DAT/2)

Bermudagrass bleaching and overall color scores were assigned at five days after the second treatment application. The bleaching was again highly evident at 5DAT/2, as was the case following the initial treatment in early August. Those treatments which now received two applications (one of which at a 0.36 lb. rate) had the greatest degree of bleaching. These scores ranged from 20% to 38% bleaching (Table 2).

The treatments which received a single initial application the month before (0.36+0, 0.18+0) and the repeat application at the low rate (0.18+0.18) had lesser bleaching (6% to 8% only) at this time (Table 2).

The single degree of freedom orthogonal contrast for rate/order application was not significant (P=0.11, F value = 2.7). However, note that the (0.36+0.18) treatment had 38% bleaching, while the (0.18+0.36) treatment had 20% bleaching. Although the F value was above 1.0 (2.7), the magnitude in variation between plot scores was too large to conclude if the initial rate had a greater effect than the accompanying second corresponding "sequential" rate (Table 2).

Mean turfgrass color scores among treated bermudagrass plugs ranged from 4.8 to 7.4. EXP31130A treatments ranged in mean scores from 4.8 to 6.4 (Table 3). In general, among 'EXP' treated plots, those treatments which received both initial and sequential treatments having at least one 0.36 lb. treatment, had the lower color scores. The initial treatment at the high rate (0.36+0) had a turfgrass mean color score essentially the same as PROGRASS, which showed no color difference in this test. The mean color score for bermuda in the control was also 7.4 (not shown) (Table 3).

September 18 (14DAT/2)

Ryegrass plot color was assigned to all plots. There were no significant differences due to herbicide applications. Generally, ryegrass color was very good and most acceptable for ryegrass as a summer turf (Table 1).

Bermudagrass plug color scores ranged from 2.6 (very poor color) to 5.6 (minimal acceptable color) among treated plots. The overall color for the check bermudagrass was 5.5 at this time (Table 3). The overall effect of herbicide treatments was significant. Again, those "EXP" turfs which received at least one 0.36 lb. application, followed by an additional application (not rate dependent) had the poorest color for bermudagrass. These treatments had mean bermudagrass color scores of only 2.6-3.9, again which is desirable (objective is to suppress bermudagrass).

September 28 (24DAT/2)

Close out color scores were taken on September 28. Clear differences in appearance of bermudagrass was evident due to herbicide treatments and the treatment effect was significant (P=0.05) (Table 3). Mean bermudagrass color scores ranged from 3.5 to 5.6 among treated bermudagrass turf. The treatment for the untreated check was 5.8.

Color scores were lowest for the (0.18+0.36) and (0.36+0.18) sequential treatments, with mean values of 3.6 and 3.5, respectively. The fact that the (0.36+0) and (0.36+0.36) treatments were not significantly different from each other is not surmised from this data. Perhaps regrowth injury response may have enhanced overall color slightly at this time. This is not unusual, as turfgrasses injured and/or slowed from herbicide and/or plant growth regulators usually exhibit a latent growth response at some later date after initial mid-term responses have occurred (Table 3).

Bermudagrass Suppression

Bermudagrass control/suppression was assessed by measuring changes in the bermudagrass growth areas for the chemical treatments before treatments were applied, and at the final close of the season on November 30, 1995. The analysis of variance conducted on July 31, 1995 showed no differences among "treatment assigned plots" before the initial treatments were applied on August 3, 1995. The F value for "treatment" for ground area covered by the bermuda on July 31 was 0.57, with a P value = 0.75. These statistics clearly show uniformity in propagule size before treatment application.

Given these facts, percent control/suppression was expressed by comparison of bermudagrass area with the initial ground cover area of bermuda on July 31. Values were analyzed and reported in percentage control (0-100%).

Changes in bermudagrass surface area ranged from 12% to 42% among treated turf via this assessment (Table 4). The F value for the herbicide main effect was 1.89, with 6,18 df using the correct ANOVA model based on the appropriate field design (P = 0.11).

The general trend for reduction in bermudagrass plant size also followed those of the other responses on bermudagrass. The sequential application at the high rate (0.36+0.36 lb.) ranked first in numerical control 42%, followed by the (0.18+0.18) and (0.36+0.18) treatments, which were calculated to both have 34% size reduction for bermudagrass. This was followed by PROGRASS (32%), the initial and single application of 'EXP' at the high rate (0.36+0 = 21%), the (0.18+0.36 treatment = 14%) and the (0.18+0) single treatment, which had a mean value of 12% for bermuda reduction. It is not clear, however, what percentage of the foliage (of the total plant cover) is/was dead at the close of the test. This can only be assessed during the green-up in the spring of 1996.
 

Based on rates and application dates under conditions of this test.

1. RP EXP31130A causes severe bleaching (loss of chlorophyll) in as little as five days after treatment (5DAT) on bermudagrass.

2. Bleaching intensity is at a maximum from 5-15 DAT, and was generally rate dependent.

3. Regrowth (or re-greening) of tissue did occur on bermudagrass, which was observed as a rate dependent response.

4. Minimal discoloration occurred on perennial ryegrass treated turf from EXP treatments.

5. Discoloration of bermudagrass in this competition study was generally greatest for the (0.36+0.36) applications.

6. Generally, bermudagrass which received sequential treatments (two applications in time) and having at least one treatment at the 0.36 lb. (high) rate, showed the greater amounts of discoloration.

7. Maximum bermudagrass suppression (42%) was achieved from the (0.36+0.36) treatments, followed by (0.18+0.18) and (0.36+0.18) EXP treatments, which both had 34% reduction in growth.

8. The extent as to the ultimate amount of "dead bermudagrass" from treatments cannot be assessed until the spring/summer of 1996.

9. A single application of EXP31130A at the 0.18 lb. rate was ineffective for inciting extensive and prolonged loss of chlorophyll, and suppression of the target weed (bermudagrass) in ryegrass turf.

10. Rates for bermudagrass control/suppression appear to be 0.36 lbs. or higher.

11. RP EXP31130A shows initial promise for bermudagrass suppression based on sequential applications.

12. The number and timing of repeat applications needs to be determined for increased efficiency for selective bermudagrass control/suppression.

13. Other opportunities exist for use of this product in turfgrass management, pending appropriate research findings.

FN:RPBERCON.95 DIR:Q196

Table 1. Mean turfgrass color scores¹ of primary ryegrass turf after application of RP EXP31130A herbicide, bermudagrass/ryegrass competition study, Summer 1995. University of Arizona.

TREATMENT	RATE2	9DAT/13	5DAT/2	14DAT/2
EXP31130A	0.18+0	7.5	8.0	8.0
EXP31130A	0.18+0.18	7.3	8.0	7.5
EXP31130A	0.18+.0.36	6.5	8.0	7.3
EXP31130A	0.36+0	7.0	8.0	8.0
EXP31130A	0.36+0.18	6.5	8.0	7.5
EXP31130A	0.36+0.36	7.3	8.0	8.0
PROGRASS	1.3+1.3	7.0	8.0	7.8
CHECK	-- --	6.5	8.0	7.8
TEST MEAN4		6.9	8.0	7.7
LSD VALUE5		NA	NA	NA

¹Color scores (1-9), 1 = dead 9 = dark green.

²Rates in lbs. AI/A.

³#/DAT/N = number of days after treatment/application sequence.

⁴Mean of all herbicide treatments.

⁵LSD Value = LSD mean separation statistic.

Table 2. Mean percent foliar bleaching¹ of bermudagrass after application of RP EXP31130A herbicide, Summer 1995. University of Arizona.

TREATMENT	RATE2	9DAT/13	15DAT/1	25DAT/1	5DAT/2
EXP31130A	0.18+0	8%	5%	3%	6%
EXP31130A	0.18+0.18	16%	8%	5%	7%
EXP31130A	0.18+.0.36	15%	11%	8%	21%
EXP31130A	0.36+0	38%	18%	6%	8%
EXP31130A	0.36+0.18	28%	21%	8%	38%
EXP31130A	0.36+0.36	33%	23%	7%	20%
PROGRASS	1.3	0%	0%	0%	2%
TEST MEAN4		19%	12%	5%	14%
LSD VALUE5		12%	8%	NA	22%

¹Percent bleaching (chlorophyll loss) of bermudagrass turf (0-100%). Values are means of four replications.

²Treatments applied in lbs. AI/A.

³#/DAT/N = number of days after treatment/application sequence. Initial application = August 3.

⁴Mean of all herbicide treatments.

⁵LSD Value = LSD mean separation statistic.

Table 3. Mean color scores¹ of bermudagrass after application of RP EXP31130A herbicide, Summer 1995. University of Arizona.

TREATMENT	RATE2	25DAT/13	5DAT/2	14DAT/2	24DAT/2
EXP31130A	0.18+0	5.6	5.9	4.5	4.6
EXP31130A	0.18+0.18	4.5	6.3	5.3	5.6
EXP31130A	0.18+.0.36	4.3	5.4	2.6	3.6
EXP31130A	0.36+0	4.3	6.4	4.8	4.3
EXP31130A	0.36+0.18	4.3	4.8	3.9	3.5
EXP31130A	0.36+0.36	4.5	5.3	3.0	4.4
PROGRASS	1.3+1.3	5.9	7.4	5.6	5.3
TEST MEAN4		4.8	5.9	4.2	4.5
LSD VALUE5		NA	1.4	1.1	1.4

¹Color scores (1-9), 1 = dead 9 = dark green. Values are means of four replications.

²Rates in lbs. AI/A.

³#/DAT/N = number of days after treatment/application sequence.

⁴Mean of all herbicide treatments.

⁵LSD Value = LSD mean separation statistic.

Table 4. Mean bermudagrass suppression¹ in perennial ryegrass turf after applications of RP EXP31130A herbicide, Summer 1995. University of Arizona, November 30, 1995.

TREATMENT	RATE2	% BERMUDA SUPPRESSION
EXP31130A	0.18+0	12
EXP31130A	0.18+0.18	34
EXP31130A	0.18+0.36	14
EXP31130A	0.36+0	21
EXP31130A	0.36+0.18	34
EXP31130A	0.36+0.36	42
PROGRASS	1.3+1.3	31
TEST MEAN3		27
LSD VALUE4		24

¹Suppression determined as reduction of bermudagrass in ryegrass turf. Values are means of four replications.

²Rates in lbs. AI/A. Applications made on 8/3/95 and 9/4/95.

³Test Mean = mean of all herbicide treated turf.

⁴LSD Value = LSD mean separation statistic.