Management and Control of Candian Thistle in Limited Access and Field Locations

Final Report for FNC01-348

Project Type: Farmer/Rancher
Funds awarded in 2001: $3,040.00
Projected End Date: 12/31/2003
Matching Non-Federal Funds: $3,650.00
Region: North Central
State: South Dakota
Project Coordinator:
Jordan Dawn
Enormous Brontosaurus Organic Farm
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Project Information


[Editor’s note: There are tables that could not be placed online. If you would like to see these tables please email us at [email protected] or call us at 800-529-1342.]

We operate a “mom and pop” vegetable farm located on 180 acres on Little Jim Creek, 15 miles north of Mitchell, SD. We grow a wide range of vegetables, melons, medicinal herbs, culinary herbs and flowers on approximately 30 rotational irrigated acres. We market most of our products at our farm market stand in Mitchell. Our planting and harvesting are all done by hand. Our tractors are used minimally for tilling, cultivating and mowing. We begin our season in January under lights and in mid March move into our greenhouse and then to the fields as weather permits and normally wrap up the season in mid October. So far, we have planted 25 acres of shelterbelt and developed 5 ponds to the farm for wildlife, irrigation and simple enjoyment. The Brontosaurus is abundant in great plains flora and fauna, especially in wet years, including fish, beavers, snapping turtles, eagles, hawks, herons, ducks, geese, purple cone flowers (Echinacea), pasque flowers, and a host of great plains and flower and other endemic great plains plant species. We also have common weed invaders, including patches of Canadian thistle.

The Enormous Brontosaurus Organic Farm has been certified organic and has been following a sustainable and organic practice since it’s inception in 1990. We are currently certified through USDA-MOSA. Philosophically and we cannot imagine farming through conventional methods, and consequently are always seeking methods to improve the general production of vegetables and hay crops and to improve the success rate of weed control. The farm encompasses a creek drainage with some areas that have limited accessibility. The Canadian Thistles in those areas create more thistle problems on our land and potentially down stream to our neighboring lands if left unmanaged. As we have been on this quarter section of land for 6 years, we have noted the problem either being stable or increasing in certain field locations and particular creek areas. The goal has been to evaluate a safe and economical method (monetarily and labor wise) to manage Canadian Thistle patches and control these areas with commonly available materials with low-tech methods.

Our objective is to find a method or multiple methods to control Canadian Thistle in specific areas. As a certified organic farm, we are not allowed to use commercial herbicides. In addition, we would rather not use toxic spray as our farm cradles the little Jim Creek drainage and is a veritable haven for wildlife, water life and flora. We need to find ways to control Canadian thistle in specific problem areas that are compatible with our farming practices and that will keep this noxious weed from spreading on our land, down the watershed and on to any neighboring properties.

Plant Description:
The following plant description is taken from Weeds of The West, by Burrill, Dewey, Cudney, Nelson, Lee and Parker through the University of Wyoming, by the Pioneer of Jackson Hole press.

Canada Thistle (Cirsum avense (L) Scop.) is a colony-forming perennial from deep and extensive horizontal roots. Stems are 1 to 4 feet tall, ridged, branching above. Leaves are alternative, lacking petioles, oblong or lance-shaped, divided into spiny-tipped irregular lobes. Flowers are unisexual, on separate plants; flowers purple (occasionally white) in heads ½ to ¾ inch long, somewhat flattened, brownish, with a tuft of hairs at the top.

Canada Thistle is a native of southeastern Eurasia. It was introduced to Canada as a contaminant of crop seed as early as the late 18th century. Canada thistle differs from other species of the true thistle in that there are male and female flower heads and these are on separate plants. By asexual reproduction, it is possible that a colony of male plants would produce no fruits, but will maintain itself. This aggressive weed is difficult to control; for example, breaking up the roots by plowing only serves to increase the number of plants. Flowering occurs during July and August.

We experimented with a variety of methods and timing. Since the experiment did not start until late May, we were forced to mow all four plots to about 4 inches in height so the vegetative material was consistent in each plot and we could apply all treatments to an even vegetative terrain. The methods we used are as follows:
1) Cover (left on the ground in sites number 3 and 4 for 1, 3 and 4 month test periods). The final coverage materials will not be removed until mid season in 2004 so we may continue longer term observations.
a. Plastic (4 mil)
i. Black
ii. Clear
b. metal (old roofing sheet metal)
c. carpet (old carpet with little glue and no foam)
d. paper
i. newspaper
ii. cardboard
2) Burning (every 2 weeks)
a. Scorching with a propane burner every two weeks
3) Tillage (fallowing every 2 weeks)
a. Rototiller
b. Slicing hoe
4) Mineral Concentrations, included pre and post soil tests on sites with visible results. Minerals were distributed on the surface of the plots in 12” bands running 12’. 25 pounds of each item was used per plot, test plot were designated as sites 1 & 2.
a. High calcium limestone
b. Sodium
c. Elemental sulfur
d. Hard rock phosphate
5) Application of 200 gain vinegar (applied every two weeks)
a. A thorough application of undiluted vinegar over test areas every two weeks
6) Combinations of B, C, D and E used in test strips with a grid system for overlap.

Four sites were chosen based on thistle infestation and access. Sites 1 and 2 were dedicated to the grid system experiments that included B through F above and were set up on a 12’ X 12’ square grid system with mineral bands running 12’ X 12’ on one direction and the other methods running perpendicularly the other (including tilling, hoeing, burning and vinegar) also running 12’ X 12’.

These sites included control plots within the grid system as well as the area surrounding the sites for comparison.

Along with the above two grid sites, we included two additional sites dedicated to the “coverage” methods listed in part 1above in this section. They were designated sites 3 and 4 and had repeating coverage materials so we might remove identical sections at 1, 3, and 4 month intervals.

In addition, we invited the assistance of local University Biologist Dr. Robert Tatina to undertake the statistical research of this project on sites 1 and 2.

Our project would not have been possible if it weren’t for the help of all the folks who assisted us. We involved as many folks as we could in the area who are interested in weed problems, environmental issues, sustainable practices and in some cases organic farming.
- Chanda Engel, SD State Extension Agent, Sanborn County. Assisted with information and advice as well as review results
- Darrell L. Deneke, SD Extension IPM Coordinator SDSU. Provided written thistle control methods through Chanda Engel.
- Appropriate Technology Transfer for Rural Areas (ATTRA), AR. Assisted with general information.
- Donna Tiede, Soil Conservationist, NRCS, advise and review results.
- Connie Vicuna, State Biologist, NRCS advise and review
- Dr. Robert Tatina, Dakota Wesleyan University, devise logistical layout and statistical findings, advise and review, develop a final report to be included in the summary project-end report
- Richard Madson, Wildlife Biologist, US Fish and Wildlife Dept., Huron, conducted a wildlife walk on the farm for the farm tour of 2002. also identified areas of wildlife habitat and species identification, weed control and general overall encouragement for our farm vision.
- Gretchen McClintock-Ames, local herbalist, Woonsocket, provided information and expertise on local herbs, and weeds and also conducted native medicinal plant walks on the farm in 2002.
- Rich Little, Tonay Haigh, Helen Little, Bruce SD; assisted with sustainable weed control suggestions and represented the Northern Plains Sustainable Agricultural Society (NPSAS) on their several visits to the farm.
- Gail Dawn provided the most valuable insights, suggestions and support as well as tracked the costs of items, kept records and assisted in the final report.
- Ken Schnieder with SARE helped with suggestions and encouragement.

The following experimental results are documented here in Dr. Robert Tatina’s report: Summary of Sampling at Enormous Brontosaurus Organic Farm, Robert Tatina, 14 October 2003.

To determine the response of plants to various weed control measures.

Materials and Methods:
Treatments were applied to two of four macroplots that were established in weedy areas. Figure 1 shows the layout of the treatment within a macroplot. On 8 and 13 August 2003 plant density was sampled. For the untreated, tilled, hoed, burned and vinegar subplots, which were rectangular, four 0.1m x 0.5 m sampling areas 0.1 m apart were established along the midline of the subplot. In these each, individual plants rooted within the sampling area were counted. For the salt, calcium, sulfur and phosphorus subplots and the combination treatment subplots, which were square, individual plants, were counted in 0.1m x 0.1m. All count data by species were then converted to density on a unit area basis of one square meter, after which the density data from the two replicate macroplots were averaged.

Table 1 shows the average density of species encountered in each subplot and the species diversity (number of species per subplot). Sixteen species were found in subplots sampled in the two macroplots. In the untreated subplot were 11 species. Reduction in species number in each treated subplot is evident (table 2). The greatest reduction (to zero) occurred in subplots treated with salt (NaCl), either alone or in combination with other treatments. The least reduction occurred in subplots treated with vinegar (7 species remaining), phosphorus (5 species remaining) and calcium with hoeing (5 species remaining). The rest of the treated subplots had two or fewer species remaining.

In the untreated subplot, eleven species were found, with the density of four of these – Canada Thistle (Cirsium arvense), field bindweed (Convolvulus arvensis), black medic (Medicago lupulina) and goosefoot (Chenopodium sp.) – representing about 85% of all the species. At an average of 26.9 individuals/m2, Canada thistle was the most abundant species. In the salt treated plots, Canada thistle was completely eliminated. While it was found in the other treatment subplots, its density was less than in the untreated subplot in most of them (table 3). The greatest reduction in the density of Canada thistle occurred in the burned (6.3/m2), vinegar-treated (8.8/m2) and vinegar with phosphorous-treated (7.5/m2) subplots. No reduction of Canada thistle seemed to be the cases in the calcium with tilling subplot (107.5/m2), the vinegar with sulfur subplot (42.5/m2) and the vinegar with calcium subplot (35/m2).

Field bindweed (Convolvulus arvensis) had lower densities in the tiled subplot, all of the salt (NaCl) subplots, the vinegar with sulfur subplot and the calcium with till subplot than in the untreated subplot (table 4). It had vinegar densities in all subplots that had been hoed, regardless of additional treatments. Highest densities for field bindweed – 40, 25 and 12.5 plants per m2 – were found in the sulfur, phosphorus and phosphorus with burning subplots respectively.

Control of goosefoot (Chenopodium sp.) seemed to be effective under all treatments except for the subplots treated with vinegar (table 5). This species differs from Canada thistle and field bindweed in being an annual. Once killed it can only come back from seed.

Black medic (Medicago lupulina) was another annual species that seemed to be eliminated or significantly reduced by all treatments (table 6).

Overall, the first year experiments were less conclusive than we had hoped. Salt produced obvious results in controlling the thistle directly in a short time and lasted all summer. However, as the attached soil reports show, the sodium buildup is not acceptable for long term field use or for streamside usage due to salt runoff. Vinegar and burning produced immediate results too, but the lasting effects appear questionable in the first year.

Tillage methods also showed obvious short term results, but again, the two week tillage timing did not exhaust the thistle plant reserves in the first season and results are affected by how moist the ground remains between tillings with the best effects in dry conditions (other rototillage observations in our shelterbelt maintenance have indicated that rototilling is generally counterproductive and is not recommended due to increases in plant populations in Canadian Thistle when tillage is done even once per month, particularly in moist conditions.)

The coverage methods also showed limited success in the plots used, but certain materials, notably metal, black plastic and carpet, showed far better resilience to the elements than others when reasonably secured, but we extrapolate that a larger coverage area may show better control with coverage techniques depending on the plants extensive root network and proximity to water and sunlight. Paper and cardboard proved to dry out quickly and pucker up, making it very vulnerable to the hot windy weather we see mid summer. We recommend against the use of paper materials due to the smaller size and migrating characteristics unless weighed down with gravel or something else. We also observed more weed intrusion between the paper test plots. One general result of this experiment is to consider a longer time period as essential to the eradication of Canadian thistle with the methods we used for all coverage materials, although we suggest using only materials that are storm resistant or made to be so. Also, rodents tended to enjoy the protection provided by the coverage materials and this could be a problem in some circumstances such as gardens or near trees.

With the exception of sodium, the mineral experiments were the least conclusive and probably need a minimum of two and possibly three seasons to show results from the break down and availability of these elements. The immediate response was certainly lacking, although some limited response is indicated in Dr. Tatinas report. In mineral experiments, other minerals could be tested, including boron, copper or others with known reactive potential either individually or in combination (a problem could be toxic residuals.)

Some combination of a mineral and tillage or fluid application (vinegar, soap, etc) may be a key to the ultimate success when coupled with timing (number of applications and time of summer…a wet or dry summer will greatly influence the results too.) Thus, the ultimate effect will be dependent on numerous factors that a farmer may or may not have control over and suppression or eradication methods will need to be adjusted for best results. It would be useful to know what methods work best in wet and dry conditions for example, along with various exposures, soil types and plant community relationships. We are unaware of any allelopathic response in Canadian thistle, compared to wormwood and other Artemisia and Salvia species.

The general effect on our operation has been the furthering of our own knowledge in methodology in the control of noxious weeds in our area. Similar experiments might be set up with wormwood and in some regions of the state with leafy spurge or St John’s Wort.

We learned that dense thistle populations can be affected by treatments of various kinds. We can see results with some of the experimental measures we employed, and we can imagine other methods that might even do better. Anyone with thistle problems should attempt to creatively control patches and share insights so we can collectively learn to solve the greater problem applying tested methods. Since the interactions of chemicals in our environment are poorly understood, it seems prudent to find the safest methods to eradicate this and other nuisance weeds on our lands with the most effective means without creating other more insidious problems in the process.

In summary, the project results represent some success in the control of Canadian Thistle. Cultivation at the right times with the right tools can be effective, especially in relation to high plant populations of beneficial plant species. Rototillage is not recommended unless done in the dry and hot part of August at least every week. Instead, we recommend slicing hoes or any method that does not churn the soil and return plant parts into the soil, especially in moist conditions. Sodium is the one mineral that showed obvious control in the first season. Other minerals might show better results in combination with vinegar/soap mix, especially if used in conjunction with a total coverage system. The coverage systems worked best with metal, partly I presume due to the heating/scorching effect from the summer sun, but black plastic and carpet worked too. The main drawback was that our experimental area was too narrow to stress the apparently large network of roots the Canadian thistle maintains in the first season. I would suggest a minimum area of coverage to be about 20’x 20’ and use a consistent coverage system that is storm worthy and has few or no breaches. We anticipate using this method next season, including some areas up to 25’ x 75’. We further recommend treating the edges with vinegar solutions and maintain this into a second season for best results. Following this treatment we then suggest planting the area into alfalfa, aggressive grasses or fast growing native grasses to establish intensive competition as soon as possible.

At the very least, mowing can keep high density thistle patches in check and avoid further reseeding. We recommend mowing when the plants are in the 12 to 20 inch stage just before flowering. Mowing must be done two to four times per summer depending on how aggressive the plants are, and that is often determined by how much moisture is available.

Another method showing promise without chemical control is with certain insects. We have chosen not to experiment with insect control of thistles at this time for several reasons. The biological control method requires larger dollar commitments, if far more difficult to evaluate due to the study of larger areas, and it might take several years to track results. Consequently we did not include this approach in this study, but it does have long term merit especially over sizeable areas and is being pursued by several agencies and individuals in the Midwest region.

Other methods of Canadian thistle control we have come across during our study are with sheep and goats. Grazing pressure might be useful if weed communities could be consistently overgrazed to reduce density and avoid seeding out, but plants might have to be grazed in the early stages for best results.

The main thing that stands out in this project is that when thick patches of Canadian thistle can be stressed out, we begin the gradual reduction of this invasive species and reduce the additional dangers inherent with chemical controls. The primary competitive advantage of this species is root and plant mass production, especially in moist conditions, good soil and with certain cultural and grazing practices that end to encourage it. Canadian thistle is an invasive species that is opportunistic, especially to wet cultivated conditions. Many plant species can compete well with this invasive perennial, but field and pasture management are crucial. Alfalfa that is cut twice per summer, for example, can often control Canadian thistle patches within it providing the stand is dense enough and grass seems to keep it in check if allowed to maintain thick enough stands. Thus good basic field and pasture management can assist any farmer in maintaining general control, and when there are specific problem areas, some of this project’s methods may serve as a relatively easy low cost alternative to managing a potentially serious noxious weed problem in the Midwest.

We have engaged several local professionals, including Dr. Tatina of DWU, Donna Tiede our local NRCS representative and Chanda Engel, our county extension agent, all of whom will receive a copy of the final report and who can assist with distributing the information. We will distribute our final report to the NPSAS conference in Bismark, in February of 2004, and the UMOFC in La Cross, in March of 2004.

We had out most recent farm tour on July14, 2002. 12 agencies were involved in the tour and had 170 people from the area attend. Preliminary weed eradication ideas were discussed and various weed species including Canadian thistle were reviewed. The SARE Canadian thistle experiment was explored and the format expanded and although it was expected to be underway, too many commitments forced us to postpone the project until this season (2003).


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.