Comparing Herbicide Programs in Identity Preserved (IP) Soybean

Co-Authors: Dr. Peter Sikkema, Dr. Clarence Swanton & Dr. François Tardif (University of Guelph)

Field studies at Elora and Woodstock have evaluated soybean herbicide treatments based on their weed control efficacy and the yield protection they provided. Important differences were found among those treatments (Table 1).

Table 1. Average visual control of broadleaf and grassy weeds and soybean yield (bu/ac) with various herbicide programs in 2009 and 2010.
Treatment

Control

Yield (bu/ac)
Broadleaves
Grasses
Conquest + Valtera*889746.1
Boundary (PRE) followed by Reflex + Pinnacle + Assure II (POST)*9410045.0
Dual II Magnum + Sencor + Lorox8910044.8
Broadstrike RC + Boundary*899944.5
Conquest808844.5
Pursuit + Valtera*909244.1
Pursuit758044.0
Broadstrike RC + Dual II Magnum779643.5
Frontier (PRE) Cleansweep (POST)8010043.4
Boundary (low rate)819742.4
Boundary (low rate) + Classic*859841.4
Cleansweep739040.6
untreated0014.7

*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).

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% visual control, the minimum level of control for a weed to be listed on a product label. (Table 2)

Table 2. Control of Tufted Vetch in soybean with herbicide programs evaluated in 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

Nightshade

The challenge with nightshade is that populations exist that are resistant to Broadstrike RC and Pursuit. The emergence pattern of nightshade also presents a challenge in that generally it has two peak emergence periods beginning in mid-May and then again in mid-June and 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. (Table 3)

Table 3. Comparative control and range in control of nightshade with herbicides applied 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%

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. (Table 4)

Table 4. Comparative control and range in control of common ragweed with herbicides applied 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%


Sow-thistles

Perennial sow-thistle is more tolerant to herbicides than annual sow-thistle, but they are both extremely difficult to manage. The expectation should be that you will not get 100% control. All herbicides evaluated were extremely variable in their control of these two species as shown in Tables 5 and 6. It is possible to achieve acceptable control when populations are low and environmental conditions are ideal.

Table 5. Comparative control and range in control of annual sow-thistle with herbicides applied in soybean
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 sow-thistle with herbicides applied in soybean
Soybean treatment, herbicide concentration, rate and application timing
Control (n=4)
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 /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%


Key Learnings from Comparative Trials

  • Two-pass” strategies offer the most consistent level of weed control.
  • One-pass” soil applied herbicide programs offer less risk then “one-pass” postemergence herbicide programs since escapes or performance issues are more easily controlled.

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.