Comparing herbicide programs in IP soybeans

With François Tardif, Clarence Swanton, and Peter Sikkema

MANAGING WEEDS IN Identity Preserved, non-GMO soybeans is a constant challenge for growers. With a magnitude of options and various species to control, accurate, non-bias data is important.

Field studies at Elora and Woodstock have evaluated herbicide treatments based on their weed control efficacy and the yield protection they provided. Important differences were found among those treatments (Table 1). This research also examined tough-to-control weeds and herbicide application techniques.

TABLE 1: Average visual control of broadleaf and grass weeds and soybean yield (bu/ac) with various herbicide programs in 2009 and 2010.

Treatment	Control(%) Broadleaves	Control (%) Grasses	Yield (bu/ac)
Conquest + Valtera*	88	97	46.1
Boundary (PRE) followed by Reflex + Pinnacle + Assure II (POST)*	94	100	45.0
Dual II Magnum + Sencor + Lorox	89	100	44.8
Broadstrike RC + Boundary*	89	99	44.5
Conquest	80	88	44.5
Pursuit + Valtera*	90	92	44.1
Pursuit	75	80	44.0
Broadstrike RC + Dual II Magnum	77	96	43.5
Frontier (PRE) Cleansweep (POST)	80	100	43.4
Prowl H20 (PRE) Cleansweep (POST)	75	99	42.9
Boundary (low rate)	81	97	42.4
Boundary (low rate) + Classic*	85	98	41.4
Cleansweep	73	90	40.6
untreated	0	0	14.7
*Not labeled tank-mixes, but may be used under the memorandum by the Pest Management Regulatory Agency regarding the use of unlabelled tank mixes. Contact the manufacturer of each product first before using to identify if they support the proposed tank-mix. Weed species present in field trials: barnyard grass, crabgrass (large), foxtail (green), witchgrass, lamb’s quarters, mustard (wild), pigweed (green and redroot), ragweed (common), vetch (tufted). Notes: Pigweed populations existed in the trials that were resistant to group 2 herbicides (e.g. Pursuit, Pinnacle, Classic, Broadstrike RC) and lambsquarters’ populations that were resistant to triazine herbicides (e.g. Sencor).

Overall, it was found that a “two-pass” strategy offers the most consistent level of control while a “one-pass” soil applied herbicide program offers less risk than a “one-pass” post-emergence herbicide program as escapes or performance issues are more easily controlled.

strategies for managing grower identified “worst weeds” in ip soybeans
Tufted Vetch: It is extremely difficult to control a perennial legume plant in an annual legume crop.

Of all herbicide programs tested, Boundary applied pre-emergence followed by Reflex + Pinnacle + Assure II provided the highest level of vetch control, albeit less than 80 percent visual control – the minimum level of control for a weed to be listed on a product label. See Table 2.

Nightshade: The challenge with nightshade is that populations exist that are resistant to Broadstrike RC and Pursuit. Nightshade generally has two peak emergence periods beginning in mid May and again in mid June and the
weed can germinate and survive in low-light environments such as a soybean
crop canopy. Therefore “two-pass” strategies have proven more consistent at controlling nightshade. See Table 3.

Common Ragweed: The biggest challenge with ragweed is that populations resistant to Broadstrike RC, Classic, FirstRate and Pursuit exist and are quite widespread. As with nightshade, “two-pass” strategies are more consistent at controlling common ragweed. See Table 4.

Sowthistles: Perennial sowthisle is more tolerant to herbicides than annual sowthistle but they are both extremely difficult to manage and you should not expect to get 100 percent control. All herbicides evaluated were extremely variable in their control of these two species, as shown in the adjacent tables. It is possible to achieve acceptable control when populations are low and environmental conditions are ideal. See Tables 5 and 6.

This project was funded in part by the Grain Farmers of Ontario and through Growing Forward, a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of several Growing Forward programs in Ontario. The assistance of OMAFRA through the OMAFRA/University of Guelph Partnership is also acknowledged. •

TABLE 2: Control of Tufted Vetch in soybean (2009-2010)

Treatment	Tufted Vetch Control (%)
Boundary (PRE) followed by Reflex + Pinnacle + Assure II (POST)*	74
Broadstrike RC + Boundary*	67
Dual II Magnum + Sencor + Lorox	62
Pursuit + Valtera*	59
Conquest + Valtera*	52
All other treatments	less than 50

TABLE 3: Comparative control and range in control of nightshade in soybeans

Soybean treatment, herbicide concentration, rate and application timing	Control (%) (n=3)	Range in control (%)
Lorox Liquid (480 g/L), 1.8 L/ac (PRE)	99	98-100
Dual II Magnum (915 g/L), 0.7 L/ac (PRE) followed by Reflex (240 g/L), 0.4 L/ac + Turbocharge 5 L/1,000L (POST)	98	94-100
Dual II Magnum (915 g/L), 0.7 L/ac (PRE) followed by Blazer (240 g/L), 1 L/ac (POST)	97	90-100
Dual II Magnum (915 g/L), 0.7 L/ac (PRE) followed by Basagran Forte (480 g/L), 0.9 L/ac (POST)	94	85-100
Broadstrike RC (80%), 35 g/ac + Dual II Magnum (915 g/L), 0.58 L/ac (POST)	89	78-99
Dual II Magnum (915 g/L), 0.7 L/ac (PRE)	87	76-93

TABLE 4: Comparative control and range in control of common ragweed in soybeans

Soybean treatment, herbicide concentration, rate and application timing	Control (%) (n=4)	Range in control (%)
Boundary (PRE) followed by Reflex (240 g/L), 0.4 L/ac + Turbocharge 5 L/1,000L (POST)	98	95-100
Boundary (PRE) followed by Blazer (240 g/L), 1 L/ac (POST)	98	96-99
Reflex (240 g/L), 0.4 L/ac + Turbocharge 5 L/1,000L (POST)	81	75-87

TABLE 5: Comparative control and range in control of annual sowthistle in soybeans

Soybean treatment, herbicide concentration, rate and application timing	Control (%) (n=5)	Range in control (%)
Classic (25%), 14 g/ac + non ionic surfactant 2 L/1,000L (POST)	95	75-100
FirstRate (84%), 8.5 g/ac + non ionic surfactant 2.5 L/1,000L + 28% UAN 25 L/1,000L (POST)	90	69-100
Blazer (240 g/L), 1 L/ac (POST)	88	65-100
Basagran Forte (480 g/L), 0.9 L/ac (POST)	86	33-100
Cleansweep + 28% UAN	84	53-100
Reflex (240 g/L), 0.4 L/ac + Turbocharge 5 L/1,000L (POST)	81	46-100

TABLE 6: Comparative control and range in control of perennial sowthistle in soybeans

Soybean treatment, herbicide concentration, rate and application timing	Control (%) (n=6)	Range in control (%)
Cleansweep + 28% UAN	85	60-100
Blazer (240 g/L), 1 L/ac (POST)	82	64-100
Basagran Forte (480 g/L), 0.9 L/ac (POST)	81	61-94
Classic (25%), 14 g/ac + non ionic surfactant 2 L/1,000L (POST)	79	51-100
FirstRate (84%), 8.5 g/ac + non ionic surfactant 2.5 L/1,000L + 28% UAN 25 L/1,000L (POST)	76	53-100
Reflex (240 g/L), 0.4 L/ac + Turbocharge 5 L/1,000L (POST)	74	54-84
Pinnacle (75%), 6 g/ac + non ionic surfactant 1 L/1,000L (POST)	73	45-86

*Not labeled tank-mixes, but may be used under the memorandum by the Pest Management Regulatory Agency regarding the use of unlabelled tank mixes. Contact the manufacturer of each product first before using to identify if they support the proposed tank-mix.