D.M. Kopec and J.J. Gilbert
University of Arizona
Abstract
IMAGE applied at 0.25, 0.25 + 0.25, and 0.38 lbs ai/A were compared to KERB treated overseeded bermudagrass turf for enhancement of spring transition. KERB treatments were made at 0.5 and 1.0 lb ai/A. At 14 DAT from an initial application of May 5, 1993, IMAGE treated turf had less ryegrass than that of the controls, but there was no difference between rates of IMAGE. By 28 DAT, a repeat application at the 0.25 lb ai/A rate improved transition, but was still not as good as a single 0.38 lb ai/A application. KERB treated turf had even lower ryegrass densities, but the high rate of KERB at 1.0 lb ai/A discolored and caused injury to the underlying Tifgreen bermuda.
Introduction
Many turfed areas in the southwestern and southeast United States overseed bermudagrass turfs in early fall in order to provide year round cover as functional turfs. Transition to bermudagrass in the spring is due to many factors which include irrigation, mechanical cultivation techniques, and bermudagrass condition shortly before or at the time of overseeding. Persistency under close mowing and improved heat tolerance of perennial ryegrass germplasm can negatively effect transition, maintaining a prolonged and sporadic ryegrass cover which minimizes a normal bermudagrass growing season before the next overseeding.
This study deals with the use of select herbicides applied to overseeded bermudagrass in order to eliminate perennial ryegrass when bermudagrass is actively growing in the spring.
Materials and Methods
A two year old Tifgreen bermudagrass turf maintained at a 7/32 inch height of cut was overseeded at rate of 22 lbs./M pure live seed on October 19, 1992, on a sand based rootzone medium at the Desert Turfgrass Research Facility, University of Arizona, Tucson, AZ. A perennial ryegrass blend of 'VIP II' was used. Plots were irrigated to prevent stress and were mowed 3x weekly. A total of 6 lbs. -N-/M was applied to the turf from November 2, 1992 to May 13, 1993 in fourteen applications of either water soluble carriers or companion cheleated iron complexes (4 applications).
Treatments applied in 1993 included the following herbicides:
1. Image (0.25 lbs. ai/A) 1 application
2. Image (0.25 lbs. ai/A) 2 applications
3. Image (0.38 lbs. ai/A) 1 application
4. Kerb (0.50 lbs. ai/A) 1 application
5. Kerb (1.0 lb. ai/A) 1 application
6. Control -- --
The first application was made on May 5, 1993, with the second respective application for Image at the 0.25 lb ai/A rate applied on May 20, 1993. Applications were made using a Co2 back-pack sprayer at 30 psi with 8004 nozzles. Final spray volume was 66 gallons per acre.
Degree of transition was determined by counting the amount of perennial ryegrass tillers within plots. Six steel washers with an inside diameter of 0.75 inch (1.76 inch2) were tossed at random onto plots. Tillers were tweezed apart to distinguish positive identification of Loliumperenne. The mean of the six sub-samples was used for analysis. A RCBD with four replications was used as the experimental design. Plot size was 6'x 6'.
Additional response variables assigned to plots included percent plot injury (0 - 100%), degree of plot injury (1 - 6, 1 = no injury, 6 = severe injury), visual density estimates (1 - 6, 1 = least, 6 = most dense), and overall turf visual quality (1 - 9, 1 = dead grass, 9 = best).
Verdure dry weights and shoot densities were taken as well from two four inch (12.57 inch2) cup-cutter samples directly after mowing on June 10, 1993.
Results and Discussion
Transition: The number of ryegrass plants present as a measure of transition was assessed on May 19 (14 DAT) and June 2, 1993 (28 DAT). On both dates, the effect of herbicide treatment was highly significant.
On May 19, the mean ryegrass density counts for the control plots was 12.8 tillers/ring, while herbicide treated turfs ranged from 4.6 to 7.5 ryegrass tillers/ring. The Kerb treated plots at 1.0 lb. ai/A had an average of 4.6 tillers/ring. Kerb at 0.50 lb. ai/A had a mean ryegrass density of 6.3 tillers/ring at this time. Image treated turf at 0.38 lbs. ai/A had 7.5 ryegrass tillers/ring. This was followed by 7.4 and 5.7 tillers/ring for each of the treatments which received the single application at 0.25 lb. ai/A 14 days earlier (Table 1).
On June 2, ryegrass densities were effected significantly by herbicides applications. The tandem application of Image at 0.25 lb ai/A was the only repeat application. The mean of the untreated control was 9.3 ryegrass tillers/ring, dropping from 12.8 from the May 19 rating. Kerb treated turfs had the lowest amounts of ryegrass. Kerb at 0.5 and 1.0 lb. ai/A rates had 2.3 and 2.6 tiller densities, respectively. There was only a slight advantage to a second application of Image at the 0.25 lb ai/A rate. The single application from May 5 now had a mean ryegrass density value of 5.9, while the repeat treatment of May 5 and 20 had 4.6. The one time application of Image at the 0.38 lb. ai/A rate had a mean density of 4.1 (Table 1). Ryegrass densities were taken again on June 29 and 30, and treated turfs were not different from those of the non-treated turfs, with an overall test mean of 3.9 (data not shown).
Turf Agronomic Responses
Injury scores: Percent injury rating scores were made on May 19, May 26 and June 2. This was 14, 21, and 28 days after initial treatment respectively, and 1 and 8 days after the repeat application of Image at 0.25 lb ai/A.
On May 19, degree of injury scores ranged from 1 to 4.8, with Kerb at the 1.0 lb. ai/A rate having the highest injury on a percent plot basis (data not shown). Kerb treated plots had the most noticeable injury symptoms of straw colored leaf tips, and slight leaf cupping. The 1.0 lb. ai/A of Kerb was moderately severe, while the same symptoms at the 0.50 lb ai/A rate was moderate (Table 2). It should be noted that the cupping and straw tipped leaves occurred on the underlying bermudagrass. By June 2, the Kerb treatments showed an accelerated response exhibiting increased turf injury (Table 2). Kerb at the 1.0 lb ai/A rate had 42% mean turf injury, followed by 13% mean injury at the 0.5 lb ai/A rate. The repeat application of Image at the 0.25 lb ai/A rate had 5% mean plot injury. The checks had no injury (Table 2).
Turfgrass color: Turfgrass color scores on May 19 ranged from 5.8 for treated turf to 7.2 for the untreated check. All treatments except Kerb at the 1.0 lb. ai/A rate had color scores of 7.0. Kerb at 1.0 lb. ai/A caused leaf tip burn and slight cupping, with tip burn causing a straw cast appearance to the bermudagrss turf. The herbicide treatment effect was P = 0.10 on May 19 (Table 3).
Mean color scores for June 2 ranged from 4.0 for Kerb treated at the 1.0 lb. ai/A rate, to 7.5 for the 0.38 lb. ai/A rate of Image. The mean of the control was 6.9. Kerb at the 0.5 lb. ai/A rate had a mean color score of 5.0, again due to straw covered leaf tips, which predominated in the canopy. The repeat application of Image at 0.25 lbs. ai/A had a slightly lower color score versus the single application at the same rate (6.3 and 6.8, respectively). (Table 3).
Shoot Density and Verdure: Visual estimates of turf densities were assigned to plots on May 19 and June 2. On May 19 Kerb treated plots had a slight decrease in visual density at the 0.5 lb. ai/A rate, (mean = 5.8), followed by a more noticeable density loss at the 1.0 lb ai/A rate (mean = 4.8). (Table 4). On June 2, the latent effects of the Kerb treatments were evident, with visual density scores of 4.3 and 3.0 for the 0.5 and 1.0 lb. ai/A treatments, respectively. Image treated turfs had density scores of 5.3, 5.5, and 6.0 for the 0.25, 0.25 + 0.25 and 0.38 lb. ai/A treatments, respectively (Table 4).
Shoot density counts were made on June 16, 1993 by harvesting two 4.0 inch cups per plot, which were then analyzed as the average. Primary shoots were counted after clipping to 1/4" above the thatch/mat surface. Kerb treated plots had the lowest number of shoots at 83, while Image treated plots had 100 - 104. The control plots averaged 104 shoots (Table 4). The level of significance was P = 0.11. No attempt was made to quantify secondary stolon development (if any).
Verdure was taken immediately after plots were double mowed on June 10, 1993. Verdure was removed with sharp clipping sheers and oven dried for 68 hours at 65C. Verdure dry weight production (grams/plug) was not affected due to herbicide applications, as mean verdure dry weights ranged from 2.9 grams to 3.4 grams among treated plots, to 3.2 for the control (Table 5).
Overall turf quality scores were assigned on May 19 and June 2. At 14 DAT, all treated turfs had slightly darker color turfs than the control. At 28 DAT, the Kerb plots had poorer turf color scores, mainly from leaftip burn and twisting/cupping of the bermuda (Table 6).
Conclusions
1. At 14 DAT, IMAGE treated turf had less ryegrass tillers than the controls when averaged across all rates. There was no difference among rates for IMAGE treated turfs at 14 DAT, however.
2. At 28 DAT, a second application of IMAGE at 0.25 lbs ai/A was better than the single application of 0.25 lbs ai/A in reducing ryegrass in overseeded bermudagrass turf.
3. A single application of IMAGE at 0.38 lbs ai/A had the least amount of ryegrass at 28 DAT, but not significantly less than the two 0.25 lb ai/A applications of IMAGE.
4. KERB at 0.5 lb ai/A had slightly more ryegrass than at the 1.0 lb ai/A rate of KERB.
5. KERB at the 1.0 lb ai/A rate caused moderate to severe turf injury, resulting in strawed leaf tips and twisted, light green colored Tifgreen bermudagrass turf.
6. The injury for KERB treated plots caused lower quality and color scores for KERB treated turf, especially at the 1.0 lb ai/A rate.
7. KERB treated turfs tended to have decreased shoot density by subjective appearance at 14 and 28 DAT. At 42 DAT, shoot counts were least among the KERB treated plots.
8. Verdure difference were not realized at 42 DAT among treatments.
9. These results differed from those for IMAGE and KERB treated turfs,
based on a previous years research completed in 1992.
FN:TRAN2YR J/A/S CLH
Table 1. Ryegrass densities1 of overseeded Tifway Bermudagrass after application of selected herbicides for spring transition. University of Arizona, 1992.
| -DATE- |
| May 19, 1993 (14 DAT) | June 2, 1993 (28 DAT) |
| Treatment2 | Rate lbs ai/A | Mean3 | Treatment2 | Rate lbs ai/A | Mean3 |
| IMAGE | 0.38 | 7.5 | IMAGE | 0.25 | 5.9 |
| IMAGE | 0.25 + 0.25 | 7.4 | IMAGE | 0.25 + 0.25 | 4.6 |
| KERB | 0.5 | 6.3 | IMAGE | 0.375 | 4.1 |
| IMAGE | 0.25 | 5.7 | KERB | 0.5 | 2.6 |
| KERB | 1.0 | 4.6 | KERB | 1.0 | 2.3 |
| Contol | -- | 12.8 | Control | -- | 9.3 |
| Test Mean | 9.6 | Test Mean | 6.6 | ||
| LSD Value4 | 2.5 | LSD Value4 | 1.8 |
1Density values are number of ryegrass plants appearing in 0.75 inch ring, six rings measured per plot, an averaged to give one value per plot.
2Treatments applied on May 5, 1992. Repeat application for IMAGE made on May 20, 1993 only. DAT = Days after treatment.
3Mean of 4 replications.
4LSD Value = least significant difference value - mean comparison statistic.
Table 2. Percent and degree1 turf injury for overseeded bermudagrass after application of selected herbicides screened for spring transition. University of Arizona, 1992.
| -DATE- |
| Degree of Injury | Percent Plot Injury |
| May 19, 1993 (14 DAT) | June 2, 1993 (28 DAT) |
| Treatment2 | Rate lbs ai/A | Mean3 | Treatment2 | Rate lbs ai/A | Mean3 |
| KERB | 1.0 | 4.8 | KERB | 1.0 | 42 |
| KERB | 0.5 | 3.0 | KERB | 0.5 | 13 |
| IMAGE | 0.25 + 0.25 | 1.3 | IMAGE | 0.25 + 0.25 | 5 |
| IMAGE | 0.38 | 1.0 | IMAGE | 0.25 | 0 |
| IMAGE | 0.25 | 1.0 | IMAGE | 0.38 | 0 |
| Control | -- | 1.0 | Control | -- | 0 |
| Test Mean | 2.0 | Test Mean | 10 | ||
| LSD Value4 | 2.0 | LSD Value4 | 6 |
1Degree of injury = 1 - 9, 1 = none, 9 = severe. Percent plot injury = (0 - 100%).
2Treatments applied May 5, 1993. Repeat application for IMAGE applied on May 20, 1993. DAT = Days after treatment.
3Mean of 4 replications.
4LSD Value = least significant difference - mean comparison statistic.
Table 6. Turfgrass quality of overseeded bermudagrass turf after application of select herbicides for spring transition.
University of Arizona, 1993.
| -DATE- |
| (14 DAT, May 19) | (28 DAT, June 2) |
| Treatment1 | Rate lbs ai/A | Mean2 | Treatment1 | Rate lbs ai/A | Mean2 |
| IMAGE | 0.25 + 0.25 | 7.5 | IMAGE | 0.38 | 8.0 |
| IMAGE | 0.25 | 7.3 | IMAGE | 0.25 | 6.8 |
| IMAGE | 0.38 | 7.0 | IMAGE | 0.25 + 0.25 | 6.8 |
| KERB | 0.5 | 7.0 | KERB | 0.5 | 4.8 |
| KERB | 1.0 | 7.0 | KERB | 1.0 | 3.5 |
| Contol | -- | 6.0 | Control | -- | 7.3 |
| Test Mean | 7.1 | Test Mean | 6.1 | ||
| LSD Value3 | 1.1 | LSD Value3 | 1.1 |
1Treatments applied on May 5, 1993. Repeat application of IMAGE 0.25 lb applied on May 20, 1993. DAT = Days after treatment.
2Mean of 4 replications. Quality = 1 - 9, 9 = best.
3LSD Value = LSD statistic. Difference between two means must be greater than the LSD Value for statistical difference between means to occur.
Table 5. Verdure weight of overseeded bermudagrass turf after treatment with select herbicides for spring transition.
University of Arizona, 1993.
| June 10, 1993 (42 DAT) |
| Treatment1 | Rate lbs ai/A | Mean2 Verdure GM. Dry WT3 |
| KERB | 0.5 | 3.4 |
| IMAGE | 0.25 + 0.25 | 3.3 |
| IMAGE | 0.25 | 3.0 |
| KERB | 1.0 | 3.0 |
| IMAGE | 0.38 | 2.9 |
| Control | -- | 3.2 |
| Test Mean | 3.1 | |
| LSD Value4 | NA |
1Treatments applied on May 5, 1993. Repeat 0.25 lb of IMAGE applied on May 20, 1993. DAT = Days after treatment.
2Mean = mean of four replications.
3Verdure = gram dry wt. from 4.0 inch diameter cup after mowing at 0.5 inch.
4LSD Value = Least significant difference value. Not applicable. P = 0.10 for herbicide effect.
Table 4. Visual estimates of overall turf density and shoot density counts of overseeded bermudagrass turf after applications of select herbicides evaluated for transition. University of Arizona, 1993.
| -DATE- | ||
| May 19 (14 DAT)
Visual Density2 |
June 2 (28 DAT)
Visual Density2 |
June 16 (42 DAT)
Shoot Density2 Counts |
| Treatment1 | Rate lbs ai/A | Mean3 | Treatment1 | Rate lbs ai/A | Mean3 | Treatment1 | Rate lbs ai/A | Mean3 |
| IMAGE | 0.25 + 0.25 | 6.0 | IMAGE | 0.38 | 6.0 | IMAGE | 0.25 + 0.25 | 104 |
| IMAGE | 0.25 | 5.8 | IMAGE | 0.25 + 0.25 | 5.5 | IMAGE | 0.38 | 100 |
| IMAGE | 0.38 | 5.8 | IMAGE | 0.25 | 5.3 | IMAGE | 0.25 | 100 |
| KERB | 0.5 | 5.8 | KERB | 0.5 | 4.3 | KERB | 0.5 | 83 |
| KERB | 1.0 | 4.8 | KERB | 1.0 | 3.0 | KERB | 1.0 | 83 |
| Control | -- | 6.0 | Control | -- | 5.7 | Control | -- | 104 |
| Test Mean | 5.7 | Test Mean | 5.0 | Test Mean | 96 | |||
| LSD Value4 | 0.4 | LSD Value4 | 0.9 | LSD Value4 | NA |
1Treatments applied on May 5, 1993. Repeat 0.25 lb of IMAGE applied on May 20, 1993. DAT = Days after treatment.
2Visual Density = 1 - 6, 1 = none, 6 = most dense. Shoot density counts = number of shoots/4 inch diameter cup.
3Mean of four replications.
4LSD Value = Least signficant difference mean separation statistic. Difference between two mean values must be greater than the LSD Value for significance between means to occur.
Table 3. Turfgrass color of overseeded bermudagrass turf after application of select herbicides for spring transition.
University of Arizona, 1993.
| -DATE- |
| (14 DAT, May 19) | (28 DAT, June 2) |
| Treatment1 | Rate lbs ai/A | Mean2 | Treatment1 | Rate lbs ai/A | Mean2 |
| IMAGE | 0.25 + 0.25 | 7.0 | IMAGE | 0.38 | 7.5 |
| IMAGE | 0.25 | 7.0 | IMAGE | 0.25 | 6.8 |
| IMAGE | 0.38 | 7.0 | IMAGE | 0.25 + 0.25 | 6.3 |
| KERB | 0.5 | 6.8 | KERB | 0.5 | 5.0 |
| KERB | 1.0 | 5.8 | KERB | 1.0 | 4.0 |
| Contol | -- | 7.2 | Control | -- | 6.9 |
| Test Mean | 6.8 | Test Mean | 6.1 | ||
| LSD Value3 | NA | LSD Value3 | 1.0 |
1Treatments applied on May 5, 1993. Repeat application of 0.25 for IMAGE applied on May 20, 1993. DAT = Days after treatment.
2Mean of 4 replications. Color = 1 - 9, 1 = straw, 9 = dark green turf.
3LSD Value = LSD statistic.
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