1998 Iowa Turfgrass Research Report
1997 Postemergence Broadleaf Weed Control Study
Barbara R. Bingaman, Nick E. Christians, and Michael B. Faust
The objective of this study was to evaluate the efficacy of various postemergence broadleaf herbicides in turfgrass. This study was conducted at the Iowa State University Horticulture Research Station north of Ames, IA. The plot was located in 'common' Kentucky bluegrass. The soil was a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with 3.2% organic matter, a pH of 7.9, 17 ppm P, and 109 ppm K. Rainfall was sporadic throughout the test so irrigation was used to maintain the bluegrass in good growing condition.
The study was designed as a randomized complete block. Individual plot size was 5 x 10 ft with three replications.
Four granular weed and feed products were included: DCDA20, DTDA20, MCDA20 and Turf Builder + 2 (Table 1). For these products the 5 x 10 ft plots were split into two-2.5 x 10 ft subplots and the north subplot was moistened with water prior to treatment and the south subplot was kept dry. One half of the material allotted for the whole plot was applied to each of the two subplots.
The balance of the herbicides were applied as liquids (Table 1). Tri-Power and Triplet were applied at 1.19, Horsepower at 0.98, Millennium at 1.10, DCDA at 0.98, DTDA at 0.98, and MCDA at 0.98 oz product/1000 ft2. Gallery 75WG was applied at 0.75 lb a.i./A as an early spring material followed by a postemergent application of either Confront 3SL at 0.75 lb a.i./A or Trimec Classic 3.4SL at 1.66 lb a.i./A. Trimec Classic 3.4SL and Confront 3SL also were applied alone postemergently at these same rates. CGA #136872 (Beacon) was applied at 20.0 g product/A and at 10.0 g product/A in split applications. SCOIL MSO, a methylated seed oil spreader, was added to the tank mix of CGA #136872 (Beacon) at 0.25% V/V. Two experimental products, EH1312 and EH1342 were applied at two different rates: EH1312 at 1.0 and 1.2 and EH1342 at 0.8 and 1.0 fl oz product/1000 ft2. Super Trimec was included at 1.1 fl oz product/1000 ft2 for comparisons. An untreated control also was included.
Liquid materials were applied at 30 psi using a CO2 backpack sprayer equipped with TeeJet™ #8006 flat fan nozzles. The materials were applied in 380 ml of water. This translates to a rate of 2 gallon/1000 ft2. Granular materials were applied with a cardboard container used as a 'shaker dispenser'.
Early spring applications (treatments 13 and 14) were made on May 15. Spring postemergent applications were made on May 22, after broadleaf weed species were established. Sequential applications (treatments 17 and 18) were made on June 19, three weeks after the initial applications.
Throughout the study, the turf was examined for phytotoxic symptoms. Phytotoxicity data were taken on July 7 and July 15 (Table 2).
Weed damage was characterized on May 30 (8 DAT) as to the type and severity of phytotoxic symptoms (Table 3). Data were taken for dandelion and clover, the two predominate broadleaf species. Damage was estimated by using a 4 to 1 scale: 4 = no damage, 3 = slight leaf curling and discoloration, 2 = moderate leaf curling and sporadic discoloration, and 1 = severe leaf curling and uniform discoloration. Additional weed damage data were taken on June 10 (19 DAT), June 19 (28 DAT), and June 26 (35 DAT). These data were assessed using a 9 to 1 scale: 9 = no damage, 8 = slight damage & no mortality, 7 = some damage & no mortality, 6 = moderate damage & 10% mortality, 5 = uniform moderate damage & 25% mortality, 4 = severe damage & 50% mortality, 3 = uniform severe damage & 75% mortality, 2 = severe damage & 90% mortality and 1 = 100% mortality (Table 4). The mortality estimations represent the reduction in all broadleaf species in each plot as compared to the untreated control plots (Table 5). Counts of the surviving weeds in each plot were taken on July 3, 1997. The number of dandelion and oxalis plants per plot were counted and the percentage of area per plot covered by clover and black medic was estimated (Table 6). These counts were converted to express percent reductions in number of plants per plot when compared with the untreated controls (Table 7).
Data were analyzed with the Statistical Analysis System (SAS, version 6.10) and the Analysis of Variance (ANOVA) procedure. Means comparisons were made using Fisher's Least Significant Difference (LSD) tests.
On July 7, phytotoxicity was noted on turf treated with CGA #136872 Beacon + SCOIL MSO (Table 2). These symptoms were still present on July 15 but were gone by July 22.
By May 30, all treated dandelion and clover plants were beginning to exhibit damage (Table 3). The observed symptoms ranged from slight leaf curling and slight discoloration to severe leaf curling and a uniform discoloration. For most herbicides, the treated dandelions had more severe damage than the clover.
All treated broadleaves were exhibiting significant levels of damage by June 19 when compared with the untreated control (Table 4). There also was some level of weed mortality in all treated plots. There was severe mortality among the broadleaves treated with Triplet, Millenium, Trimec Classic 3.4SL, and Super Trimec by June 26 (Table 5). On this date, 25 herbicides produced significant reductions in broadleaf cover when compared with the untreated control (Table 5). Reductions were „ 70% for seven herbicides and there was a 90% broadleaf reduction in turf treated with Super Trimec.
Treatment with 21 of the herbicides resulted in dandelion numbers that were significantly less than the untreated control (Table 6). Percentage reductions in dandelions were > 80% in turf treated with either Triplet, MCDA, Gallery 75WG + Confront 3SL, Confront 3SL, Super Trimec, and MCDA20 (on wet foliage) (Table 7). Control of dandelions was better for DCDA20, DTDA20, MCDA20, and Turf Builder + 2 applied to wet foliage than applied to dry foliage.
Populations of the annual broadleaf, oxalis, were quite high this year. Oxalis numbers were higher in some of the treated plots than in the untreated control (Table 6). When compared to the untreated control, Super Trimec produced an 80% numerical reduction in the oxalis population, although statistically this reduction was not significant (Table 7).
Some of the treated turf had a higher percentage clover cover than the untreated control (Table 6). Millenium, Gallery 75WG + Confront 3SL, Confront 3SL, and Super Trimec treated turf contained no clover. Turf treated with either Tri-Power, Triplet, Horsepower, CGA #13872 (Beacon) at 10 g product/A in split applications, DCDA20 (on wet foliage), or MCDA20 (on wet foliage) had percentage clover reductions „ 90% (Table 7).
All but one of the herbicides produced significant reductions in black medic percentage cover when compared with the untreated control (Table 7). Treatment with 22 of the materials resulted in reductions in black medic populations „ 93% (Table 7).
Table 1. Rates and timing of application for broadleaf herbicides used in the 1997 Postemergence Broadleaf Weed Control Study.
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(POST) |
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Materials |
product/1000 ft2 |
/plot |
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Untreated control |
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Tri-Power [60.36%]1 |
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Triplet [49.67%]1 |
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Horsepower [59.40%]1 |
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Millenium[55.80%]1 |
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DCDA [47.06%]1 |
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DTDA [47.33%]1 |
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MCDA [58.04%]1 |
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DCDA201&2 [dry foliage] |
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DTDA201&2 [dry foliage] |
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MCDA201&2 [dry foliage] |
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Turf Builder + 21&2 [dry foliage] |
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(POST) |
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lb a.i./A |
/plot2 |
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(lb a.i./A) |
/plot |
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Gallery 75WG [FN-3133] + Confront 3SL [XRM-5085]3 |
none |
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0.75 |
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Gallery 75WG [FN-3133] + Trimec Classic 3.4SL3 |
none |
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1.66 |
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Trimec Classic 3.4SL3 |
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Confront 3SL [XRM-5085]3 |
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(POST) |
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(3 weeks after initial) 5 |
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product/A |
/plot2 |
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product/A |
/plot |
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CGA #136872 (Beacon) + SCOIL MSO4 |
20.00 g + .25% v/v |
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CGA #136872 (Beacon) + SCOIL MSO4 |
10.00 g + .25% v/v |
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10.00 g +.25%v/v5 |
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(POST) |
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fl oz product/1000 ft2 |
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Trimec Classic 3.4SL6 |
1.0 |
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EH13126 |
1.0 |
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EH13126 |
1.2 |
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EH13426 |
0.8 |
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EH13426 |
1.0 |
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Super Trimec |
1.1 |
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product/1000 ft2 |
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DCDA201&2 [wet foliage] |
4.00 lb |
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DTDA201&2 [wet foliage] |
4.00 lb |
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MCDA201&2 [wet foliage] |
4.00 lb |
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Turf Builder + 21&2 [wet foliage] |
2.94 lb |
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1These materials were screened for Riverdale Chemical Co.
2Test plots receiving these materials were divided into two - 2.5 x 10 ft [25 ft2] subplots and the north subplot was moistened before application and the south subplot was kept dry.
These materials were screened for DowElanco3, and Novartis [Ciba]4 .
5Sequential applications were made on June 19 approximately 3 weeks after the initials.
6These materials were screened for PBI/Gordon.
Early spring applications (PRE) (trts 13 & 14) made on May 15; Spring applications (POST) made on May 22. Sequential (3 WAT) materials (trts 17 & 18) were applied June 19.
380 ml water per plot is equivalent to 2 gal/1000 ft2.
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ISU Horticulture:Publications:1998 Turfgrass Report | College of Agriculture |