Canada thistle control with selective herbicides

Transcription

1 Canada thistle control with selective herbicides Canada thistle is an invasive weed that poses a problem in minimally mowed rough areas. Steven McDonald, M.S. Dan Loughner, M.S. Minimally mowed rough areas (also referred to as no-mow areas, secondary rough areas or naturalized areas) are common on golf courses and are used to enhance aesthetics and playability and to reduce maintenance inputs such as mowing and chemical applications (4). Although often referred to as naturalized, these areas are not truly naturalized because they are mowed and often planted with non-native plant materials (such as Festuca species). Therefore, we will refer to these areas as minimally mowed rough. A troublesome weed Canada thistle (Cirsium arvense [L.] Scop.) is a perennial weed that frequently invades minimally mowed rough on golf courses. It is classified as a noxious weed in many regions of the U.S. including the upper Midwest, Northeast and mid- Atlantic. Many superintendents report it as the Canada thistle contamination in a mature hard fescue minimally mowed rough area in June. Photos by S. McDonald single most problematic weed to control (personal communication). Canada thistle spreads through wind-dispersed seeds and a fibrous, spreading root system in which new sprouts emerge. Although seed dispersal is important to colonization of new areas, vegetative reproduction may be more important in established colonies. Canada thistle has an extensive network of both deep roots and horizontal spreading roots. Once established, this root system serves as a large carbohydrate reserve, which aids in plant survival after freezing, tillage, mowing and chemical treatments. Additionally, the roots can spread 15 feet or more from the mother plant and can produce new plants from adventitious buds on the roots at 2- to 6-inch (5- to 15-centimeter) intervals, thus greatly increasing the size and competitive ability of the colony (2,6). Canada thistle has a very aggressive growth habit and will outcompete many grasses. This weed emerges from underground roots and from seed in late spring and will continue to emerge with warm humid weather. In the mid-atlantic region, Canada thistle emerges from mid to late April, producing seed from May through July. It is particularly difficult to manage this weed when desirable cool-season grasses are becoming established because fescue turfs are sensitive to herbicides and grow slowly. Many superintendents report unacceptable control of Canada thistle with herbicides, perhaps because of its extensive underground root system. Biological control of Canada thistle using 86 GCM July 2009

2 insects that feed on the seedheads and various bacteria and fungi has been investigated in other crops and does not appear to be acceptable or costeffective (3,5). In many crops and turfgrass systems, herbicides are relied on to provide acceptable levels of control of Canada thistle. Currently, superintendents are managing minimally mowed rough by mowing one to three times annually. The grass is allowed to grow long and produce a seedhead, which adds to the aesthetic appeal of these areas. However, not mowing these areas on a regular schedule creates other pest problems like Canada thistle. Pre-emergent herbicides can be used to control annual grassy weeds and some broadleaf weeds. This research investigated various herbicides for Canada thistle control. Materials and methods Sites on two golf courses in southeastern Pennsylvania were chosen for these Canada thistle control evaluations. Both sites were historically maintained as naturalized rough where herbicides and mowing were used to manage Canada thistle. For more detailed site descriptions, see Table 1. Chemical treatments Chemical treatments were applied using a flatfan nozzle (8004) and mixed with 44 gallons of water/acre (411.6 liters/hectare) at a boom height of 20 inches (51 centimeters) above the soil surface. Treatments were applied in the morning with dew present. No irrigation was applied following treatment. Pre-emergent herbicide applications were made on April 3, 2008, and post-emergent applications were made on May 15, Canada thistle was approximately 6 inches (15 centimeters) tall with seven to nine leaves when post-emergent applications were made. The May 15 timing corresponds to common practice used by superintendents in the mid-atlantic region and should be considered early post-emergent. No seedheads were present on the Canada thistle. Evaluation of treatments Evaluations consisted of assessment of Canada Site descriptions thistle injury and weed control associated with various treatments. Injury (epinasty) was rated on a 0 to 5 scale, where 0 is no foliar injury and 5 is completely brown, dead weed. Control was assessed on a percentage basis scale where 0 = no control and 100 = complete control. Evaluations were initiated after post-emergent applications, with Canada thistle injury being assessed seven and 14 days after treatment and control at 30 and 60 days after treatment. Desirable grass species found in the test area were not affected (Above) Canada thistle contamination in a newly seeded fine fescue area. (Below) Herbicide injury to an immature stand of hard fescue following a herbicide application targeting Canada thistle. Site Location Soil ph Primary grass species Bellewood Golf Club Pottstown silt loam % hard fescue (Festuca brevipilia, formerly F. trachyphylla) and 25% creeping red fescue (F. rubra) Five Ponds Golf Course Warminster silt loam % tall fescue (F. arundinacea) and 40% other fine fescue (Festuca species) Table 1. Descriptions of the research sites. July 2009 GCM 87

3 Products tested Application Product Active ingredient Manufacturer timing/use Targeted weeds Barricade 65 WDG prodiamine Syngenta pre-emergent annual grassy weeds, some broadleaf weeds Dimension 2EW dithiopyr Dow AgroSciences pre-emergent annual grassy weeds, some broadleaf weeds Confront triclopyr + clopyralid Dow AgroSciences post-emergent broadleaf weeds and some woody Gallery 75DF isoxaban Dow AgroSciences pre-emergent control or suppression of various broadleaf weeds Fusilade II fluazifop-p-butyl Syngenta post-emergent perennial and annual grassy weeds Trimec Classic 2,4-D, MCPP, dicamba PBI Gordon Corp. post-emergent broadleaf weeds Table 2. Name, manufacturer, application timing and targeted weeds for all products tested. Treatments and rates Treatment and formulation Application Rate product/1,000 square feet Gallery 75DF pre 0.5 ounce Dimension 2EW pre 0.73 fluid ounce Barricade 65 WDG pre 0.4 ounce Gallery 75DF + Confront pre + post 0.5 ounce fb 0.74 fluid ounce Dimension 2EW + Confront pre + post 0.73 fluid ounce fb 0.74 fluid ounce Barricade + Confront pre + post 0.4 ounce fb 0.74 fluid ounce Confront post 0.74 fluid ounce Gallery 75DF + Confront + Fusilade II + NIS pre + post + post 0.5 ounce fb 0.74 fluid ounce fluid ounce Dimension 2EW + Confront + Fusilade II + NIS pre + post + post 0.73 fluid ounce fb 0.74 fluid ounce fluid ounce Barricade + Confront + Fusilade II + NIS pre + post + post 0.4 ounce fb 0.74 fluid ounce fluid ounce Fusilade II + NIS post 0.5 ounce Gallery 75DF + Trimec Classic pre + post 0.5 ounce fb 1.2 fluid ounces Dimension 2EW + Trimec Classic pre + post 0.73 fluid ounce fb 1.2 fluid ounces Barricade + Trimec Classic pre + post 0.4 ounce fb 1.2 fluid ounces Trimec Classic post 1.2 fluid ounces Untreated Pre, Pre-emergent treatments applied on April 3, Post, Post-emergent treatments applied on May 15, Post + post indicates treatments were applied as a tank mixture. fb, followed by. Rates after fb are application rates for post-emergent treatments. NIS, non-ionic surfactant. Table 3. Treatment, formulation, application code and rate of herbicides evaluated. by any herbicide treatments; therefore, no results are included in this article. Data were subjected to analysis. Data from both sites were not significantly different from each other; therefore, data tables show the average of both sites for injury rating and percent control at 15 days after treatment. Treatments evaluated Sixteen individual herbicide or herbicide combination treatments were evaluated. Treatments consisted of six different herbicides applied alone or in various tank mixtures and replicated four times at two different golf courses. Herbicide, formulation, application date and rates are listed in Tables 2 and 3. Pre-emergent applications of Gallery, Dimension and Barricade were made at a conventional spring timing (April 3, 2008), and post-emergent applications of Confront, Trimec Classic and Fusilade were made on May 15, The non-ionic surfactant Activator 90 was added at 0.25% (volume to volume) to all treatments containing Fusilade II according to label recommendations. Fusilade was tank-mixed with Confront at the post-emergent timings noted in Tables 2 and 3 (that is, post + post). Canada thistle injury results Canada thistle emerged at both sites in late April. Pre-emergent treatments alone did not appear to have any effect on Canada thistle development (Table 4). Following the post-emergent applications, the 88 GCM July 2009

4 Post-emergent herbicide injury Bellewood Data averaged over both sites 7 DAT 15 DAT Treatment Application Injury (0-5) Gallery 75DF pre 0b 0b Dimension 2EW pre 0b 0b Barricade 65 WDG pre 0b 0b Gallery 75DF + Confront pre + post 4.20a 3.9a Dimension 2EW + Confront pre + post 4.43a 4.0a Barricade + Confront pre + post 4.35a 4.0a Confront post 4.35a 4.0a Gallery 75DF + Confront + Fusilade II pre + post + post 4.43a 4.0a Dimension 2EW + Confront + Fusilade II pre + post + post 4.28a 3.6a Barricade + Confront + Fusilade II pre + post + post 4.30a 3.8a Fusilade II + NIS post 0.18b 0b Gallery 75DF + Trimec Classic pre + post 4.15a 3.7a Dimension 2EW + Trimec Classic pre + post 4.28a 4.0a Barricade + Trimec Classic pre + post 4.28a 4.0a Trimec Classic post 4.40a 4.0a Untreated 0b 0b Pre, Pre-emergent treatments applied on April 3, Post, Post-emergent treatments applied on May 15, Post + post indicates treatments were aplied as a tank mixture. Injury data were collected on the same day (15 DAT) and were not statistically different when averaged over both sites; therefore data are presented as the mean of both sites. Means in a column followed by the same letter are not significantly different. DAT, days after treatment. Injury was rated on a 0 to 5 scale where 0 = no visible injury and 5 = completely dead weed. Means in a column followed by the same letter are not significantly different from each other. Table 4. Injury to Canada thistle following post-emergent herbicide applications. Injury to Canada thistle in trial area following applications of Confront and Trimec Classic. The plots that are covered with thistle were either Fusilade-alone, the pre-emergent treatments-only or untreated controls. highest level of injury was observed for treatments containing Confront or Trimec Classic (Table 4). Injury levels did not increase or decrease when pre-emergent herbicides were applied in conjunction with Confront and Trimec Classic. Fusilade alone caused limited injury to Canada thistle and did not enhance the performance of Confront when applied as a tank mixture. Canada thistle control results Pre-emergent only treatments The pre-emergent treatments alone did not provide significant control of Canada thistle at the rates evaluated (Table 5). Combination treatments All combination programs containing Confront and Trimec Classic provided greater than 82% control of Canada thistle at 30 days after treatment (Table 5). Canada thistle control did not improve when pre-emergent herbicides were applied before post-emergent applications of Confront and Trimec Classic. Likewise, control associated with Confront was not enhanced when tank-mixed with Fusilade. By 60 days after treatment at both sites, the level of control dropped among all treatments containing Confront and Trimec Classic to a range of 68.1% to 76.2% control. There were no significant differences among treatments containing Confront or Trimec Classic at 30 and 60 days after treatment at either site. Post-emergent only treatments Confront and Trimec Classic provided the highest level of Canada thistle control among treatments employing only a post-emergent herbicide application. There was no significant difference between herbicides at 30 and 60 days after treatment at the Five Ponds site. At the Bellewood site, Confront was significantly more effective than Trimec Classic (all data not shown). Fusilade was ineffective against Canada thistle at both study sites. It is important to note that the control decline between the 30 and 60 days after treatment evaluations could be due to movement of underground root structures from the surrounding plot area, insufficient herbicide to provide systemic control of underground root structure, or possible germination of new seedlings. Overall conclusions and future research Results indicate that Canada thistle is a difficult perennial weed to control in minimally mowed rough areas. There was no benefit from 90 GCM July 2009

5 V vv % Canada thistle control Data averaged over both sites 30 DAT 60 DAT Treatment Application % control Gallery 75DF pre 0e 0d Dimension 2EW pre 0e 0d Barricade 65 WDG pre 0e 0d Gallery 75DF + Confront pre + post 93.0a 68.1c Dimension 2EW + Confront pre + post 92.1ab 76abc Barricade + Confront pre + post 92.8a 77.2a Confront post 92.1ab 76.2a Gallery 75DF + Confront + Fusilade II pre + post + post 97abc 75.5ab Dimension 2EW + Confront + Fusilade II pre + post + post 92.1 ab 72.6abc Barricade + Confront + Fusilade II pre + post + post 91.6ab 76.6a Fusilade II + NIS post 0e 0d Gallery 75DF + Trimec Classic pre + post 86.8bcd 75.0abc Dimension 2EW + Trimec Classic pre + post 84.8d 71.0abc Barricade + Trimec Classic pre + post 87.2a-d 69.2bc Trimec Classic post 85.5cd 73.0abc Untreated 0e 0d Pre, Pre-emergent treatments applied on April 3, Post, Post-emergent treatments applied on May 15, DAT, days after treatment. Post + post indicates that the treatments were applied as a tank mixture. Percent control data were averaged over both sites. Means in a column followed by the same letter(s) are not significantly different. NIS, non-ionic surfactant. Table 5. Percent Canada thistle control by all treatments at both sites. The research says Canada thistle is a troublesome weed in minimally mowed rough areas in the U.S.; it spreads readily through wind dispersal and an extensive root system. Sixteen treatments, including pre-emergent and post-emergent and combinations of pre- and post-emergent products, were evaluated on two different golf courses in southeastern Pennsylvania. The pre-emergent treatments alone did not provide significant control of Canada thistle at the rates evaluated. Among the post-emergent applications evaluated, Confront and Trimec Classic provided the highest level of control. Mowing three times per year may, by itself, decrease the vigor of Canada thistle. applying Barricade, Dimension or Gallery as a pre-emergent for Canada thistle control, and no benefit was expected because these herbicides are not labeled for control of Canada thistle. Fusilade II applied alone or in a tank mixture with Confront had no effect on Canada thistle. Fusilade II is not labeled for control of Canada thistle. Confront and Trimec Classic provided a reduction in Canada thistle coverage at both evaluation dates. Control decreased between the evaluations at 30 and 60 days after treatment, indicating a second post-emergent herbicide application may have been beneficial days after the first post-emergent treatment. Mowing alone may decrease the vigor of Canada thistle. Research conducted in irrigated pastures in Colorado showed that mowing pastureheight grasses to a height of 3 to 4.7 inches (7 to 12 centimeters) three times annually for two seasons controlled 85% of Canada thistle (1). Therefore, an integrated approach may be to mow Canada thistle before it produces a seedhead and to mow twice more afterward during the year. Many other herbicides are available to superintendents for post-emergent control of Canada thistle in roughs. Future research should evaluate cultural practices and other herbicides for longterm control of Canada thistle and turfgrass tolerance to create an integrated management plan for this invasive weed. Acknowledgments We thank the grounds crew and superintendents at Bellewood GC, Pottstown, Pa., and Five Ponds GC, Warminster, Pa., for the space and flexibility to conduct these trials. Literature cited 1. Beck, G.K., and J.R. Sebastian Combining mowing and fall-applied herbicides to control Canada thistle (Cirsium arvense). Weed Technology 14: Hanson, B. Canada thistle (Circium arvense). College of Natural Resources, University of Idaho. edu/range454/2003_pet_weeds/canada_thistle_web page.html (verified June 1, 2009). 3. Hoeft, E.V., N. Jordan, J. Zhang and D.L. Wyse Intergrated cultural and biological control of Canada thistle in conservation tillage soybean. Weed Science 49: Ostmeyer, T A look for the ages: Native landscaping has carved a solid niche in today s golf course development and management. Golf Course Management 68(11): Reed, C.C., D.L. Larson and J.L. Larson Canada thistle biological control agents on two South Dakota wildlife refuges. Natural Areas Journal 26(1): USDA, NRCS (United States Department of Agriculture, Natural Resources Conservation Service) The Plants Database. (April 2000) (verified June 1, 2009). GCM Steven J. McDonald (turfgrassdiseasesolutions@yahoo. com) is the president of Turfgrass Disease Solutions LLC in Spring City, Pa. Dan Loughner is a field scientist with Dow AgroSciences in Princeton, N.J. 92 GCM July 2009