CANADA FLEABANE. Conyza canadensis L. ANNUAL/WINTER ANNUAL: Reproduces by seed An over-wintered rosette in winter wheat during late April.

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CANADA FLEABANE Conyza canadensis L. ANNUAL/WTER ANNUAL: Reproduces by seed An over-wintered rosette in winter wheat during late April.

EMERGENCE PATTERNS Seeds are viable at maturity and will germinate throughout the year provided soil temperature are warm enough (Weaver, 2001).

Tozzi and colleagues (2014) found that the majority of seed will germinate from August to November, but a second germination window exists from mid-may to Mid-June.

FLUENCE TILLAGE Burying seed in the soil will lower germination, with no seed germinating when buried 6 cm deep and 90% reduction in germination when buried 1 cm deep

Small seedling plants are most susceptible to tillage operations, however in preliminary tillage trials, even small seedlings when at high population densities will hold

Larger rosettes have developed roots systems that are quite resilient at holding soil and surviving tillage operations.

1 CANADA FLEABANE Conyza canadensis L. ANNUAL/WTER ANNUAL: Reproduces by seed An over-wintered rosette in winter wheat during late April. A seedling rosette (15 cm in diameter) during late October. EMERGENCE PATTERNS Seeds are viable at maturity and will germinate throughout the year provided soil temperature are warm enough (Weaver, 2001). Soil temperatures above C are preferred for seed germination. Tozzi and colleagues (2014) found that the majority of seed will germinate from August to November, but a second germination window exists from mid-may to Mid-June. Fall germinated seedlings will form a rosette while spring germinated seedling will typically by-pass the rosette stage and go straight to bolting. FLUENCE TILLAGE Burying seed in the soil will lower germination, with no seed germinating when buried 6 cm deep and 90% reduction in germination when buried 1 cm deep (Weaver, 2001). Small seedling plants are most susceptible to tillage operations, however in preliminary tillage trials, even small seedlings when at high population densities will hold soil tightly to their roots, increasing their chances of survival. Larger rosettes have developed roots systems that are quite resilient at holding soil and surviving tillage operations. Regardless, tillage will reduce the population density of Canada fleabane, but one should not expect 100% control. Glyphosate-resistant populations of Canada fleabane exist throughout Ontario. The following table illustrates the level of control achieved with various rates of glyphosate applied to resistant populations. Small fleabane seedlings that survived a tillage pass. The fluffy mature flowers that are ready for wind dispersal. Comparing the average and range in control of glyphosate-resistant Canada fleabane over a number of trials evaluated at eight weeks after the application of glyphosate at three rates. 3 L/ac (2.7 kg/ha) 2 L/ac (1.8 kg/ha) A plant during the bolting stage The small, white and much branched flowers of Canada fleabane. 12 PROBLEM WEED GUIDE 13

CORN Control of glyphosate-resistant Canada fleabane has been most consistent with post-emergence herbicide applications but good control can be achieved with pre-emergence herbicides providing this

Post-emergence applications of Marksman, Engenia or Xtendimax, Pardner + Aatrex 480 and Distinct are also effective on glyphosateresistant Canada fleabane.

2 CORN Control of glyphosate-resistant Canada fleabane has been most consistent with post-emergence herbicide applications but good control can be achieved with pre-emergence herbicides providing this weed is emerged. Of the pre-emergence herbicides, Integrity, Marksman, Callisto + Aatrex 480, Battalion, and Engenia or Xtendimax are all good options. Post-emergence applications of Marksman, Engenia or Xtendimax, Pardner + Aatrex 480 and Distinct are also effective on glyphosateresistant Canada fleabane. Aggressive primary tillage prior to planting to small fleabane rosettes can also be very effective. BEST HERBICIDE OPTIONS CORN Applications made prior to crop emergence (pre-emergence), but to emerged Canada fleabane. Canada fleabane control in mid-june following a pre-emergence application of Marksman (dicamba/atrazine). You can see the population density of Canada fleabane in the unsprayed strip to the right. MARKSMAN (dicamba/atrazine) TEGRITY (saflufenacil/dimethenamid-p) CALLISTO + AATREX LIQUID 480 (mesotrione + atrazine) 1.8 L/ac (1.8 kg/ha) 445 ml/ac (735 g/ha) 120 ml/ac ml/ac (140 g/ha + 1 kg/ha) BATTALION co-pack (rimsulfuron + s-metolachlor + dicamba) 20 ac/case rate ENGENIA or XTENDIMAX 400 ml/ac or 680 ml/ac (0.6 kg/ha) CONVERGE XT (isoxaflutole + atrazine) 174 ml/ac L/ac (105 kg/ha kg/ha) PRIMEXTRA II MAGNUM (s-metolachlor/atrazine) 1.6 L/ac (2,880 g/ha) AATREX 480 (atrazine) 1.24 L/ac (1.49 kg/ha) Canada fleabane control in mid-june following a pre-emergence application of Aatrex 480 (atrazine) at the highest labelled rate. 14 PROBLEM WEED GUIDE 15

CORN Applications made to emerged weeds and crop (post-emergence). MARKSMAN (dicamba/atrazine) 1.8 L/ac (1.8 kg/ha) 96 91-99 5 ENGENIA or XTENDIMAX 400 ml/ac or 680 ml/ac (0.

25% v/v + 1.25% v/v (0.2 kg/ha) 93 78-100 5 89 65-97 5 Canada fleabane control in mid-june following a post-emergence application of Banvel II.

3 CORN Applications made to emerged weeds and crop (post-emergence). MARKSMAN (dicamba/atrazine) 1.8 L/ac (1.8 kg/ha) ENGENIA or XTENDIMAX 400 ml/ac or 680 ml/ac (0.6 kg/ha) PARDNER + AATREX 480 (bromoxynil + atrazine) DISTCT + non-ionic surfactant + 28% UAN (diflufenzopyr/dicamba) 400 ml/ac L/ac (280 g/ha kg/ha) 115 g/ac % v/v % v/v (0.2 kg/ha) Canada fleabane control in mid-june following a post-emergence application of Banvel II. You can see the population density of Canada fleabane in the unsprayed strip to the left. VIOS G3 (420 g/l) + BANVEL II (tembotrione/thiencarbazonemethyl) + 44 ml/ac ml/ac (37.5/7.5 g/ha g/ha) CALLISTO + AATREX 480 (mesotrione + atrazine) 85 ml/ac ml/ac (100 g/ha g/ ha) PEAK + BANVEL II (prosulfuron + dicamba) 5.3 g/ac ml/ac + 0.2% v/v (10 g/ha g/ha) ARMEZONE + AATREX ASSIST + 28% UAN (topramexone + atrazine) 15 ml/ac ml/ac + 0.5% v/v % v/v (12.5 g/ha g/ha) LIBERTY 200 SN* (glufosinate ammonium) (500 g/ha) VIOS G3 (420 g/l) (tembotrione/ thiencarbazone-methyl) 44 ml/ac (37.5/7.5 g/ha) AATREX CROP OIL (atrazine) 1.24 L/ac + 1% v/v (1.49 kg/ha) *Can only be applied to Liberty Link corn hybrids Canada fleabane control has been more variable with some post-emergence herbicides, such as Callisto + Aatrex PROBLEM WEED GUIDE 17

SOYBEANS Glyphosate-resistant Canada fleabane is most difficult to control in soybean because few options exist to control it once the soybean crop has emerged.

However, as that treatment was evaluated over several seasons and locations, about one third of the time, glyphosate + Eragon + Merge failed to provide commercially acceptable control of

4 SOYBEANS Glyphosate-resistant Canada fleabane is most difficult to control in soybean because few options exist to control it once the soybean crop has emerged. Therefore it must be controlled prior to planting. When research trials were initially done, the pre-plant tank-mix of glyphosate + Eragon + Merge was the most effective option. However, as that treatment was evaluated over several seasons and locations, about one third of the time, glyphosate + Eragon + Merge failed to provide commercially acceptable control of glyphosate-resistant Canada fleabane. To address this inconsistency, different tank-mix options were evaluated and over two seasons the addition of Sencor 75 DF at 215 g/ac to glyphosate + Eragon + Merge improved control of glyphosate-resistant Canada fleabane. The equivalent rate of metribuzin in Sencor 75 DF can also found in herbicides like Conquest LQ and Canopy Pro. The introduction of Roundup Ready 2 Xtend soybean cultivars to the marketplace in 2017 will allow farmers to apply the active ingredient dicamba (e.g. Engenia, Xtendimax) to control glyphosate resistant weeds such as Canada fleabane. Field trials conducted by the University of Guelph have demonstrated that dicamba applied at the highest labeled rate and to emerged Canada fleabane rosettes prior to soybean planting have provided the most effective control of glyphosate resistant Canada fleabane. BEST HERBICIDE OPTIONS SOYBEANS Applications made prior to planting (pre-plant) but to emerged Canada fleabane. An infestation of glyphosate-resistant Canada fleabane in soybean. Glyphosate-resistant Canada fleabane in soybean during July that was not controlled by a pre-plant application of glyphosate at 2.7 kg ai/ha Tank-mix partners with glyphosate Tank-mix partners with glyphosate + ERAGON LQ (saflenacil) + SENCOR 75 DF (metribuzin) + MERGE ml/ac (25.2 g/ha) g/ac (400 g/ha) L/ac SENCOR 75 DF (metribuzin) + BROADSTRIKE RC (flumtesulam) g/ac (1,120 g/ha) + 35 g/ac (70 g/ha) ERAGON LQ + MERGE (saflenacil) ml/ac L/ac (25.2 g/ha) FIRSTRATE (chloransulam-methyl) Source: H. Byker, University of Guelph + 17 g/ac (35 g/ha) Source: C. Budd, University of Guelph 18 PROBLEM WEED GUIDE 19

+ TEGRITY (saflufenacil/dimethenamid-p) Tank-mix partners with glyphosate* + 150 ml/ac (247 g/ha) 16 0-35 11 84 5-100 8 Pre-plant applications of dicamba at the high rate and to emerged fleabane

5 + TEGRITY (saflufenacil/dimethenamid-p) Tank-mix partners with glyphosate* ml/ac (247 g/ha) Pre-plant applications of dicamba at the high rate and to emerged fleabane rosettes have provided the most effective control of glyphosate resistant Canada fleabane (left) compared to an unsprayed strip (right). A follow-up, post-emergence application of dicamba may be necessary when new seedlings have germinated following crop emergence. + GRAMAXONE (200 g/l) (paraquat) L/ac (1,100 g/ha) ERAGON LQ + MERGE (saflenacil) + CLASSIC (chlorimuron-ethyl) + FIRSTRATE (chloransulam-methyl) ml/ac L/ac (25.2 g/ha) + 14 g/ac (9 g/ha) + 17 g/ac (35 kg/ha) SOYBEANS Herbicide options only for Roundup Ready 2 Xtend Soybean cultivars. + LIBERTY 200 SN (glufosinate ammonium) + 2,4-D ESTER 700 (660 g/l) (2,4-D) + (500 g/ha) ml/ac (528 g/ha) Source: H. Byker, University of Guelph *Tank-mixing of Valtera or Aim EC with glyphosate provided less than 50% control of Canada fleabane Pre-plant application timing 340 ml/ac or 200 ml/ac 680 ml/ac or 400 ml/ac Post-application timing 340 ml/ac or 200 ml/ac Sequential (applied pre-plant and then again post-emergence) 340 ml/ac or 200 ml/ac PROBLEM WEED GUIDE 21

Control of Canada fleabane when tank-mixing Sencor 75DF at 300 g/ac with glyphosate.

of Canada fleabane, but one third of the time it has provided very poor control in

The addition of Sencor 75 DF at 216 g/ac to that tank-mix improves consistency of

6 Control of Canada fleabane when tank-mixing Sencor 75DF at 300 g/ac with glyphosate. A pre-plant application of glyphosate + Eragon + Merge can provide very good control of Canada fleabane, but one third of the time it has provided very poor control in research trials. The addition of Sencor 75 DF at 216 g/ac to that tank-mix improves consistency of control compared to the unsprayed strip on the right. Control of Canada fleabane when tank-mixing Sencor 75DF at 600 g/ac with glyphosate. 22 PROBLEM WEED GUIDE 23

CEREALS Infinity is the most effective at controlling Canada fleabane in winter wheat, spring wheat and spring barley. Lontrel 360 is also an effective option if growing spring wheat and barley.

7 CEREALS Infinity is the most effective at controlling Canada fleabane in winter wheat, spring wheat and spring barley. Lontrel 360 is also an effective option if growing spring wheat and barley. POST-CEREAL HARVEST Once the cereal crop is harvested, a greater amount of sunlight will hit the soil surface and will either stimulate new weed germination or growth of Canada fleabane that was suppressed by the cereal canopy. To minimize Canada fleabane seed being produced and returned to the soil, an aggressive cover crop (e.g. oats, rye, clover, oilseed radish) should be planted. Alternatively, fall tillage should be done no later than 4-6 weeks after harvest, before weed seed reaches maturity. BEST HERBICIDE OPTIONS CEREALS Applications made to emerged weeds and winter wheat (post-emergence). LONTREL 360 (clopyralid) FITY (pyrasulfotole/bromoxynil) 0.22 L/ac (0.2 kg/ha) 0.33 L/ac (213 g/ha) Control of Canada fleabane with Infinity as seen just prior to harvest. The spray swath in research trials is typically 2 m wide (4 nozzles). So to the left and right of the relatively clean swath of wheat below are unsprayed strips. 2,4-D ESTER (660 g/l) (2,4-D) DICHLORPROP-D (582 g/l) (dichlorprop/2,4-d) 0.52 L/ac (850 g/ha) 0.7 L/ac (1.017 kg/ha) TROPHY [TROPHY A + TROPHY B] (fluroxypyr + MCPA) 0.24 L/ac L/ac (108 g/ha g/ha) MCPA ESTER (600 g/l) (MCPA) 0.56 L/ac (850 g/ac) BUCTRIL M (560 g/l) (bromoxynil/mcpa) 0.4 L/ac (0.56 kg/ha) REFE M [REFE SG + MCPA] + non-ionic surfactant (thifensulfuron-methyl/ tribenuronmethyl + MCPA) 12 g/ac L/ac + 0.2% v/v (15 g/ha kg/ha) PEAK + PARDNER + non-ionic surfactant (prosulfuron + bromoxynil) 5.3 g/ac L/ac + 0.2% v/v (10 g/ha g/ha) CITATIONS Tozzi, E., Lyons, M. and R.C. Van Acker The effect of simulated winter warming spells on Canada fleabane (Conyza canadensis L. Cronq. var. canadensis) seeds and plants. Canadian Journal of Plant Science. 94(5): Weaver, S.E The biology of Canadian weeds Conyza canadensis Can. J. Plant Sci. 81: Conyza canadensis (L.) Cronq. 24 PROBLEM WEED GUIDE 25

Chapter 14: Difficult to Control Weeds

Chapter 14: Difficult to Control Weeds 335 Management strategies for difficult to control weeds Problem perennial and biennial weeds are challenging to control because they typically have extensive root