CANADA THISTLE CONTROL IN SPRING WHEAT |
William W. Donald
Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U. S. Department of Agriculture and does not imply its approval to the exclusion of other products that also may be suitable.
INTRODUCTION
The increasing shift to no-till or reduced tillage cereal production in the Northern Great Plains of the United States and Canada has created a farming environment favoring the encroachment of perennial weeds, such as Canada thistle, smooth bromegrass, and foxtail barley. Canada thistle is also a concern in "conventional" tillage farming systems employing either chisel or moldboard plowing for primary tillage (Dexter, et al. 1981). Canada thistle is troublesome because of its extensive, spreading root system and adventitious root buds which produce new daughter shoots (Moore, 1978).
Canada thistle can be highly competitive with spring wheat (Hodgson, 1955; Hodgson, 1968). Only 2 plants/yd(2) (2 plants/m(2)) reduced yield 15%, whereas 25 plants/yd(2) (30 plants/m(2)) reduced yield 60%. Consequently, control strategies must reduce Canada thistle densities to 1 plant/yd(2) (1 plant/m(2)) or less to minimize or prevent spring wheat yield losses.
No-till dryland farmers in the Northern Great Plains can control perennial weeds by applying high rates of RoundupÆ (glyphosate) or BanvelÆ (dicamba) in the fall after wheat harvest to prevent or decrease Canada thistle shoot emergence in the following growing season. Both herbicides damage cereals if they are applied directly to the crop at the high rates (0.75 to 1.5 lb ai or ae/A) (0.8 to 1.7 kg/ha) needed to damage Canada thistle roots. Fall treatment is probably the best management strategy for dense stands of Canada thistle in the short-term, but it is not necessarily the best strategy from an economic standpoint. More than one fall treatment is needed to eradicate Canada thistle roots of dense stands. Drought in the Northern Great Plains may reduce the effectiveness of fall-applied herbicides for long-term Canada thistle control. Variable weather may render a multiyear control strategy ineffective that relies on annual fall re-treatment with these expensive herbicides.
The objective of this field research was to find a strategy, other than fall-applied herbicides, to manage Canada thistle in no-till spring wheat. Various in-crop herbicides were applied to the same no-till plots of spring wheat for three years to evaluate their relative efficacy and characterize their long-term effects on Canada thistle roots taken from soil cores.
MATERIALS AND METHODS
This field experiment was a randomized complete block design with three blocks. Plots measured 10 by 40 feet (3.3 by 12.8 m). The no-till site at Fargo, North Dakota, was heavily infested with Canada thistle (25 to 50 plants/m~). All plots were treated with Roundup at 0.35 lb ae/ha (0.39 kg ae/ha) plus surfactant X-77 at 0.25% v/v before planting. Either 'Len' or 'Wheaton' semidwarf hard red spring wheat was planted 2 inches (5 cm) deep in 7 inch (17.5 cm) rows at 75 lb/A (85 kg/ha) with a double disk no-till grain drill. Nitrogen fertilizer was banded 4 inches (10 cm) deep between alternate rows for a yield goal of 50 bu/A (3360 kg/ha) as recommended by soil test. Supplemental phosphorous and potassium were not needed. All annual grass weeds were controlled with postemergence-applied HoelonÆ (diclofop) at 1 lb ai/A (1.1 kg/ha). Herbicides for Canada thistle and annual broadleaf weed control were also applied postemergence (Table 1). Control ratings at harvest, Canada thistle density, and wheat yield were determined. In the fall after harvest, 15 soil cores per plot (each 3 inches diam. by 20 inches; 7.2 cm diam. by 50 cm deep) were taken. Thickened, propagative Canada thistle roots (~> 0.05 inch or 1.3 mm diam.) were washed free of soil (Carlson and Donald, 1986) and root length, fresh weight, and the number of visible adventitious root buds were determined.
RESULTS AND DISCUSSION
ExpressÆ (DPX-L5300), GleanÆ (chiorsulfuron), and CurtailÆ (clopyralid plus 2,4-D) provided consistently good control (-> 80%) of Canada thistle shoots at wheat harvest (Table 1). Shoot control with Formula 40Æ (2,4-D amine) was poor in the first year but improved with annual reapplication for three growing seasons. Brominal 3+3Æ (MCPA plus bromoxynil) usually was superior to 2,4-D amine, but was inferior to ExpressÆ, GleanÆ, and CurtailÆ for Canada thistle shoot control.
| Table 1. Effect of herbicides on visually evaluated Canada thistle control in no-till hard red spring wheat (0% = no control of shoots; 100% = no shoots present). | ||||||
| Canada thistle control | ||||||
| 1985 | 1986 | 1987 | ||||
| Treatment | Rate | 8/5 | 6/12 | 8/7 | 5/19 | 7/30 |
| lb ai or ae/A (g ai/ha) | % (a) | |||||
| Untreated | 0 c | 0 b | 0 d | 0 c | 0 b | |
| MCPA + Bromoxynil (Brominal 3+3) | 0.25 + 0.25 (280 + 280) | 87 a | 0 b | 73 b | 42 b | 81 a |
| 2,4-D amine (Formula 40) | 0.5 (560) | 40 b | 0 b | 53 c | 35 bc | 90 a |
| 2,4-D + clopyralid (Curtail) | 0.25 + 0.25 (280 + 60) | 92 a | 17 b | 93 a | 70 ab | 97 a |
| Chlorsulfuron(b) (Glean | 0.03 (30) | 95 a | 63 a | 98 a | 88 a | 97 a |
| DPX-L5300(b) (Express) | 0.01 (10) | 80 a | 0 b | 93 a | 45 b | 85 a |
| a Means in a column followed by the same letter were not different at P = 0.05 by Duncan's multiple range test. b(x)-77 surfactant at 0.25% (v/v) added. | ||||||
All herbicide treatments reduced Canada thistle shoot density by harvest after two and three years with the greatest decreases by GleanÆ, CurtailÆ, 2,4-0 alone and Brominal 3+3Æ (Table 2). Only GleanÆ and CurtailÆ reduced shoot density below 1 plant/yd(2) (1 plant/m(2)) after three years.
| Table 2. Effect of herbicides on Canada thistle shoot density in no-till hard red spring wheat. | ||||||
| Canada thistle density | ||||||
| 1985 | 1986 | 1987 | ||||
| Treatment | Rate | 8/14 | 5/20 | 8/13 | 5/24 | 7/27 |
| lb ai or ae/A (g ai/ha) | no./m(2) (a) | |||||
| Untreated | - | 25 a | 27 a | 50 a | 15 ab | 50 a |
| MCPA + Bromoxynil (Brominal 3+3) | 0.25 + 0.25 (280 + 280) | 14 bc | 25 ab | 22 bc | 6 cd | 8 cd |
| 2,4-D amine (Formula 40) | 0.5 (560) | 24 a | 22 ab | 32 b | 18 a | 4 cd |
| 2,4-D + clopyralid (Curtail) | 0.25 + 0.25 (280 + 60) | 11 cd | 18 a-c | 14 cd | 5 d | 0.5 d |
| Chlorsulfuron(b) (Glean | 0.03 (30) | 5 cd | 2 c | 1 c | 0.3 d | 0.2 d |
| DPX-L5300(b) (Express) | 0.01 (10) | 20 ab | 11 bc | 33 b | 8 b-d | 15 bc |
| a Means in a column followed by the same letter were not different at P = 0.05 by Duncan's multiple range test. Six 0.25 m(2) quadrats were sampled per plot. b(x)-77 surfactant at 0.25% (v/v) added. | ||||||
Two or three years of repeated treatment with GleanÆ or CurtailÆ in wheat reduced Canada thistle root biomass, length, and adventitious root bud numbers to 7% or less of control values (Table 3).
| Table 3. Effect of herbicides applied in no-till hard red spring wheat on Canada thistle roots. | |||||||
| Root fresh weight | Root length | Root bud number | |||||
| Treatment | Rate | 1986 | 1987 | 1986 | 1987 | 1986 | 1987 |
| lb ai or ae/A (g ai/ha) | g/m(2) (a) | m/m(2) a | no./m(2) (a) | ||||
| Untreated | - | 3630 a | 2290 | 640 a | 400 a | 8280 a | 9880 a |
| Chlorsulfuron(b) (Glean | 0.03 (30) | 80 c | 60 | 20 c | 7 b | 240 c | 160 b |
| DPX-L5300(b) (Express) | 0.01 (10) | 1440 b | 1360 | 270 b | 330 a | 4060 b | 5500 ab |
| 2,4-D + clopyralid (Curtail) | 0.25 + 0.25 (280 + 60) | - | 150 | - | 30 b | - | 320 b |
| a Means in a column followed by the same letter were not different at P = 0.05 by Duncan's multiple range test. b(x)-77 surfactant at 0.25% (v/v) added. | |||||||
Wheat yield was an insensitive measure of the relative effectiveness of the herbicides for Canada thistle control (Table 4). Wheat in herbicide-treated plots yielded two- to three-fold more than in Canada thistle-infested control plots, but differences in yield between herbicide treatments could not be detected despite dramatic differences in Canada thistle shoot density (Table 2) and control (Table 1).
| Table 4. Effect of herbicides for Canada thistle control on hard red spring wheat yield in no-till. | ||||
| Wheat yield | ||||
| Treatment | Rate | 1985 | 1986 | 1987 |
| lb ai or ae/A (g ai/ha) |
bu/A (a) | |||
| Untreated | - | 13 b | 8 b | 8 b |
| MCPA + Bromoxynil (Brominal 3+3) | 0.25 + 0.25 (280 + 280) | 25 a | 27 a | 36 a |
| 2,4-D amine (Formula 40) | 0.5 (560) | 24 a | 20 a | 31 a |
| 2,4-D + clopyralid (Curtail) | 0.25 + 0.25 (280 + 60) | 24 a | 26 a | 40 a |
| Chlorsulfuron(b) (Glean | 0.03 (30) | 31 a | 28 a | 43 a |
| DPX-L5300(b) (Express) | 0.01 (10) | 25 a | 22 a | 29 a |
| a Means in a column followed by the same letter were not different at P = 0.05 by Duncan's multiple range test. A small plot combine was used to harvest the wheat and yield was adjusted to 12% moisture content. b(x)-77 surfactant at 0.25% (v/v) added. | ||||
Concern about the spread and development of hard-to-control perennial weeds, such as Canada thistle, acts as a deterrent to adoption of no-till. This research demonstrates that repeated applications of Glean~ or Curtail@ over three years both controlled Canada thistle shoots and reduced root growth, while increasing wheat yields.
LITERATURE CITED
Carlson, S. J. and W. W. Donald. 1986. A washer for removing thickened roots from soil. Weed Sci. 34:794-799.
Dexter, A. G., J. D. Nalewaja, D. D. Rasmusson, and J. Buchli. 1981. Survey of wild oats and other weeds in North Dakota 1978 and 1979.
N.D. State Univ. Res. Rep. 79.
Hodgson, J. M. 1955. The influence of Canada thistle stand on yield of small grains. Res. Progr. Rep. West. Weed Control Conf. pp. 4-5.
Hodgson, J. M. 1968. The nature, ecology, and control of Canada thistle. U. S. Dep. Agric. Tech. Bull. 1386.
Moore, R. J. 1975. The biology of Canadian weeds 13: Cirsium arvense (L.) Scop. Can. J. Plant Sci. 55:1033-1048.