D.D. Minner, F. Valverde, and S.K. Lee
Introduction
Broadleaf weeds such as white clover (Trifolium repens) and dandelion (Taraxicum officinale) are a problem on many turf sites. These problem weeds are seldom controlled with a single application of currently available broadleaf herbicides.
The purpose of this study was to evaluate the efficacy of several post-emergency broadleaf weed control herbicides applied in a single application.
Materials And Methods
This study was conducted in Ames, Iowa at the Iowa State University Horticulture Research Station from July 10 to August 29, 2002. Following the recommendations on the suitable area for the study, the trial was set on a mature stand of Kentucky bluegrass (Poa pratensis) infested with a uniform population of white clover and a very low population of Dandelion. The turf was routinely irrigated and mowed at 2.5 inches. Urea-nitrogen was applied at 1.0 lb N/1000 sq.ft. two weeks prior to herbicide treatment.
Treatments were arranged in a Randomized Complete Block design with 3 replications and 14 treatments (Table 1). Each replication had 14 individual 6 x 4-ft plots including a non-treated control. Treatments were applied using a CO2 backpack sprayer on July 16, 2002. The delivery rate of the sprayer was 125 gallons/A. Control plots only received a water spray.
Table 1. Treatment description and rate of application.
| 1-RIV 01-02 1.6 oz./M | 8-RIV 10-02 1.1 oz./M |
| 2-RIV 02-02 1.3 oz./M | 9-RIV 11-02 1.1 oz./M |
| 3-RIV 03-02 1.1 oz./M(not applied) | 10-RIV 12-02 1.1 oz./M |
| 4-RIV 04-02 1.1 oz./M | 11-RIV 13-02 1.1 oz./M |
| 5-RIV 05-02 .9 oz./M | 12-RIV 20-02 .9 oz./M |
| 6-RIV 06-02 .9 oz./M | 13-RIV 21-02 1.1 oz./M |
| 7-RIV 07-02 1.1 oz./M | 14-Control |
Treatment three was listed on protocol, but was not received in shipment. However, it was treated (just water) and evaluated as any other treatment.
Data collection involved a visual estimation of the percent of the plot area covered by white clover at 9 and 29 days after treatment (DAT). When rating at 9 DAT some plants of white clover did not die completely; therefore weed color was used to further evaluate herbicidal activity on a scale of 1 to 9, where 9 is a healthy green weed and 1 was a necrotic brown weed. Turf phytotoxicity was visually assessed on a color scale; data for this variable were collected prior to treatment and at 29 DAT. A similar scale was used for this purpose, where 9 is a healthy green grass plant and 1 is completely brown.
Even though no initial data was collected on dandelions due to its scarce presence, the population of this weed increased abruptly in several plots after treatment. A visual estimation of the percent ground coverage of this species was done at 44 DAT.
Data were analyzed with Statistical Analysis System (SAS, Version 8.0) and Analysis of Variance procedure (ANOVA). Treatment effects were tested using Fisher's Least Significant Difference (LSD) mean separation test.
Results
The study area had a uniform stand of white clover as evident from non-significant differences between plots prior to treatment. Statistically significant differences in coverage and color of white clover occurred on July 25 and August 14, 2002, respectively (Table 2).
Table 2. Analysis of variance for turf broadleaf herbicide study.
| Before treatment (July 10) | 9 DAT (July 25) | 29 DAT (August 14) | |
|---|---|---|---|
| Coverage of White Clover | NS | ** | ** |
| Color of White Clover | n/a | ** | ** |
** Significant at the _ = 0.01 probability level, NS = not significant.
Compared to the control, all broadleaf herbicides significantly reduced the amount of white clover (Table 3). There were few differences among herbicides and rates with the exception of RIV03-02 (as expected), which resulted in less control of white clover. Treatments RIV4-02, RIV7-02 and RIV20-02 showed the minimum coverage of white clover by the end of the study. However, those that showed a greater reduction (based on initial and final population) were RIV04-02 and RIV07-02.
Table 3. Percentage of White Clover (Trifolium repens) coverage on 2 different dates after herbicide application.
| Coverage of White Clover (%) | Change of % cover | ||||
|---|---|---|---|---|---|
| Treatments | Before treatment (July 10) | 9 DAT (July 25) | 29 DAT (August 14) | July16-July25 | July16-Aug.14 |
| RIV 01-02 1.6 oz./M | 23.330 | 10.67cd | 16.667b | -12.67 | -6.67b |
| RIV 02-02 1.3 oz./M | 33.330 | 16.00cd | 20.00b | -17.33 | -13.33b |
| RIV 03-02 1.1 oz./Mz | 23.330 | 26.67b | 73.33a | 3.33 | 50.00a |
| RIV 04-02 1.1 oz./M | 36.670 | 10.67cd | 11.67b | -26.00 | -25.00b |
| RIV 05-02 0.9 oz./M | 40.000 | 12.33cd | 18.33b | -27.67 | -21.67b |
| RIV 06-02 0.9 oz./M | 30.000 | 10.67cd | 13.33b | -19.33 | -16.67b |
| RIV 07-02 1.1 oz./M | 40.000 | 15.67cd | 11.67b | -24.33 | -28.33b |
| RIV 10-02 1.1 oz./M | 36.670 | 18.33bc | 20.00b | -18.33 | -18.67b |
| RIV 11-02 1.1 oz./M | 26.670 | 8.67d | 20.00b | -18.00 | -6.67b |
| RIV 12-02 1.1 oz./M | 30.000 | 11.33cd | 16.67b | -18.67 | -13.33b |
| RIV 13-02 1.1 oz./M | 33.330 | 13.33cd | 16.67b | -20.00 | -16.67b |
| RIV 20-02 0.9 oz./M | 26.670 | 11.67cd | 11.67b | -15.00 | -15.00b |
| RIV 21-02 1.1 oz./M | 30.000 | 14.33cd | 15.00b | -15.67 | -15.00b |
| Control | 26.670 | 36.67a | 86.67a | 10.00 | 60.00a |
| LSD(_ = 0.05) | 22.66 NS | 8.45 ** | 14.88 ** | NS | ** |
** Significant at the _ = 0.01 probability level, NS = not significant.
z Treatment not applied
When evaluating the weed plants that survived treatments (Table 4), it is observed that RIV13-02 caused greater damage to white clover although not statistically different than 4 other treatments.
Table 4. Color of White Clover (Trifolium repens) on 2 different dates after herbicide application.
| Treatment | 9 DAT (July 25) | 29 DAT (August 14) |
|---|---|---|
| RIV 01-02 1.6 oz./M | 7.33b | 7.67a |
| RIV 02-02 1.3 oz./M | 7.00bc | 7.67a |
| RIV 03-02 1.1 oz./Mz | 9.00a | 7.67a |
| RIV 04-02 1.1 oz./M | 5.67cde | 6.67bc |
| RIV 05-02 0.9 oz./M | 5.00de | 6.33cd |
| RIV 06-02 0.9 oz./M | 5.00de | 6.33cd |
| RIV 07-02 1.1 oz./M | 6.00bcde | 6.67bc |
| RIV 10-02 1.1 oz./M | 7.33b | 7.00abc |
| RIV 11-02 1.1 oz./M | 6.33bcd | 7.00abc |
| RIV 12-02 1.1 oz./M | 7.00bc | 7.00abc |
| RIV 13-02 1.1 oz./M | 4.67e | 5.67d |
| RIV 20-02 0.9 oz./M | 7.00bc | 7.33ab |
| RIV 21-02 1.1 oz./M | 6.33bcd | 6.67bc |
| Control | 9.00a | 7.67a |
| LSD(_ = 0.05) | 1.49 ** | 0.88 ** |
** Significant at the _ = 0.01 probability level, NS = not significant.
z Treatment not applied
None of the herbicide treatments resulted in visible phytotoxicity that caused turfgrass browning or necrosis; however, there were slight differences in turf color (Table 5). Although the differences were slight, RIV20-02 had a significantly lower turf color than the control.
The Kentucky bluegrass turf remained actively growing during the entire study with no evidence of grass injury by treatments or environmental conditions.
Table 5. Color of Kentucky bluegrass (Poa pratensis) on 2 different dates.
| Before treatment (July 10) | 29 DAT (August 14) | |
|---|---|---|
| RIV 01-02 1.6 oz./M | 6.67 | 8.00a |
| RIV 02-02 1.3 oz./M | 6.00 | 8.00a |
| RIV 03-02 1.1 oz./Mz | 7.00 | 8.00a |
| RIV 04-02 1.1 oz./M | 6.33 | 8.00a |
| RIV 05-02 0.9 oz./M | 6.67 | 7.67ab |
| RIV 06-02 0.9 oz./M | 6.33 | 7.67ab |
| RIV 07-02 1.1 oz./M | 6.67 | 8.00a |
| RIV 10-02 1.1 oz./M | 6.33 | 8.00a |
| RIV 11-02 1.1 oz./M | 6.33 | 7.67ab |
| RIV 12-02 1.1 oz./M | 6.00 | 8.00a |
| RIV 13-02 1.1 oz./M | 6.00 | 7.67ab |
| RIV 20-02 0.9 oz./M | 6.33 | 7.33b |
| RIV 21-02 1.1 oz./M | 6.00 | 8.00a |
| Control | 6.33 | 8.00a |
| LSD(_ = 0.05) | 1.44 NS | 0.5879 |
NS = not significant.
z Treatment not applied
The dandelion population was not prevalent in the study area during treatment; however, treatment differences were noticeable after completion of the study. Therefore, a final rating of dandelion was conducted 44 DAT.
Table 6. Percent ground coverage of Dandelion observed 44 DAT.
| Treatment | Percent coverage 44 DAT |
|---|---|
| RIV 01-02 1.6 oz./M | 5.67d |
| RIV 02-02 1.3 oz./M | 13.33bcd |
| RIV 03-02 1.1 oz./Mz | 22.67ab |
| RIV 04-02 1.1 oz./M | 7.33d |
| RIV 05-02 0.9 oz./M | 7.33d |
| RIV 06-02 0.9 oz./M | 14.00bcd |
| RIV 07-02 1.1 oz./M | 14.00bcd |
| RIV 10-02 1.1 oz./M | 20.67abc |
| RIV 11-02 1.1 oz./M | 5.00d |
| RIV 12-02 1.1 oz./M | 13.33bcd |
| RIV 13-02 1.1 oz./M | 21.33abc |
| RIV 20-02 0.9 oz./M | 9.67cd |
| RIV 21-02 1.1 oz./M | 10.67bcd |
| Control | 29.33a |
| LSD(_ = 0.05) | 12.07 |
z Treatment not applied
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ISU Turfgrass:2003 Turfgrass Report | College of Agriculture |
Contents ©1995-2003, ISU Horticulture Department