Bermudagrass can be a problem in mixed turfs with perennial ryegrass. Four repeat applications (1 month) of TURFLON ESTER (1.0 lb. AI/A), ACCLAIM (0.38 lb. AI/A) and a tank mix of the two were made to a perennial ryegrass turf with introduced 'Midiron' bermudagrass. Three applications were necessary to induce control levels of 40% or more. The tank mix was generally more effective than TURFLON ESTER alone. ACCLAIM alone was ineffective at the rate and timing conditions tested here. A maximum of 56% control was achieved (as percent live foliage reduction) after four treatments by the tank mix. It appears that closer application timings are needed for control of bermudagrass in perennial ryegrass under desert conditions when using rates tested here.

Bermudagrass, when not the primary desired turf, is a problematic ground cover. Elimination of bermudagrass by cultural means in a mixed polystand is essentially impossible. Usually a full renovation of the area is often the remedy which includes loss of all vegetation from use of a non-selective herbicide (glyphosate) or from a sterilization treatment. Repeated use of a selective herbicide would be beneficial if (1) activity against bermuda is demonstrated and (2) tolerance to ryegrass is acceptable.

A three year old stand of turf-type perennial ryegrass was used to test the efficacy of two herbicides for bermudagrass suppression at the University of Arizona's Desert Turfgrass Research Facility in Tucson during the summer of 1994.

Treatments included TURFLON ESTER applied at 1.0 lb. AI/A, ACCLAIM applied at 0.38 lb. AI/A, a tank mix at the above rates, and an untreated control (check plot). Each treatment appeared five times in a randomized complete block design. Plot size was 5' X 8'. Each plot received two 4" plugs of the cultivar 'Midiron' as transplants on June 6. The plugs received a 500 ppm solution of water soluble -N- on June 17, in addition to a 0.25 lb. -N-/M application to the entire field the day after transplanting. The turf site was mowed regularly to 2.5 inches whenever it reached 3.0 inches with a rotary push mower and irrigated at 100% reference ET from the on-site weather station which used a Penman based atmospheric model. The soil was a Gila sandy loam, with a pH of 7.6.

The treatments were applied on June 22, July 21, August 19 and September 20, 1994. All treatments were applied using a Co₂ sprayer at 30 psi with 8004 nozzles producing a final delivery solution rate of 66 GPA. Treatments dried 16 hours before being irrigated.

Response variables included the following measurements and estimates. For each individual plug (two per plot) plant radius was measured in two perpendicular directions (for an average radius) as an indication of plant growth/suppression. These measurements were made on July 22, August 18, September 6 and October 6. Mean radius data was expressed as percent control based on the mean of the check plots [1-(treated/check)] X 100.

Injury scores were assigned to plugs on July 22 and again on October 6 using a subjective scale of 1-6 where 1 = no injury, 2 = slight, and 6 = dead turf. Injury scores are analyzed directly. Percent live bermuda was estimated on a per plug basis on September 9 and October 6 and was analyzed as the percent control compared to the check plot mean.

Data was analyzed using the ANOVA technique on SAS software using the least squares technique. Mean separation was accomplished by using Tukey's Honest Least Significant Difference Values only if P values for treatment effects were P = 0.05 or less. The replication X treatment interaction was used as the proper error term for measuring treatment effects in order to avoid over inflation of the true error mean square.

The various evaluations were made at 30, 28, 18 and 16 days after each respective monthly application.

Injury to bermuda:
Visual injury was significant among treated plots on both July 22 and September 6. TURFLON ESTER (1.0 lb. AI/A) and the TURFLON ESTER/ACCLAIM tank mix (1.0 lb. and 0.38 lb. AI/A, respectively) produced the greatest amount of injury (mean scores of 2.4). The ACCLAIM applied alone at 0.38 lb. AI/A produced only slight injury to the bermudagrass (mean score = 1.5). This occurred at 30DAT from application number 1 (Table 1).

On September 6 (18DAT from application number 3), mean injury scores ranged from 1.0 (none) to 4.4 (moderate-severe) among treatments. The tank mix after three applications was showing the most injury (4.4 mean score), followed by TURFLON ESTER alone (Table 1). TURFLON ESTER was slightly more active than ACCLAIM alone (2.7 and 2.2, respectively).

Percent live bermuda:
Percent live bermuda was a visual estimate of the percentage of the entire bermudagrass foliage which was green and healthy (0-100%). It was not an assessment of plant size. Estimates were made on September 9 (18 DAT/App.3) and on October 6 (16DAT/App.4). Data was expressed as percent control of check plot means. For both dates, the treatment effect was significant. The tank mix provided 37% control of bermuda, followed by TURFLON ESTER alone (13% control) and ACCLAIM alone (4% control) on September 6 (Table 2).

On October 6 (16DAT/App.4) a greater level of control was achieved. TURFLON/ACCLAIM (tank mix) had 56% mean control, TURFLON ESTER alone had 51% control. ACCLAIM alone had only 6% control when assessed as the percent live bermuda.

Plant radius:
Plant radius measurements were made (in cm.) on four dates and treatment effects were significant on one of these dates (18DAT/3 on September 6.) It took three applications before a statistical reduction in bermudagrass radius could be detected. At the close of the test on October 6, (16DAT/4) plant reduction was significant at P = 0.15 only (Table 3).

On July 22 (30DAT/1), the percent radius reductions reached only 5% for both TURFLON ESTER and the TURFLON ESTER/ACCLAIM tank mix. ACCLAIM alone had no real effect (1% mean reduction). On August 18 (28DAT/2), percent radius reductions ranged from 14% to 17%, with the ACCLAIM having the lowest radius reduction (14%). On September 6 (18DAT/3), there were significant differences among treatment means. The tank mix had caused a 45% reduction, TURFLON ESTER alone caused a 30% reduction, followed by ACCLAIM alone with 27% reduction.

On October 6, daytime temperatures were still relatively warm, but night temperatures were ranging in the 60 to 65F degree range. The tank mix had 35% control, TURFLON ESTER had 24% control, while ACCLAIM had 18% radius control. The decreased control at this time (16DAT/4) may be due from decreased activity from shorter day length response of the bermuda coupled with decreased night temperature. Although percent radius control was less at October 6 than September 9 (Table 3), the percent live bermuda was not (Table 2). This indicated some regrowth after the third application followed by necrosis afterwards. At no time was there visual injury notable to the perennial ryegrass.

2. After three applications (30 days apart) significant reductions in plant injury and percent radius reduction occurred.

3. The tank mix was generally superior to that of TURFLON ESTER alone, which was generally more effective than ACCLAIM alone.

4. ACCLAIM applied alone, was not effective for bermudagrass suppression at the 0.38 lb. AI/A rate.

5. At the rates tested, either earlier applications and/or more frequent applications appear necessary for greater suppression of bermuda under the conditions of this test.

Table 1. Plant injury scores¹ to 'Midiron' bermudagrass after applications of select herbicides in a perennial ryegrass turf. University of Arizona, 1994.

Table 3. Mean percent plant radius reduction¹ of 'Midiron' bermudagrass from select herbicides in perennial ryegrass turf. University of Arizona, 1994.

FN:TRIBERM.94 O/N/D CLH