How late can you apply post emergent soybean herbicides without causing significant injury and yield reductions? Most herbicide labels specify a maximum crop stage (Table 1). A three year study by Dr. Peter Sikkema reveals that of all the herbicides tested, Pursuit (imazethapyr) and Pinnacle SG (thifensulfuron) should not be applied at advanced crop stages (between the 5th trifoliate stage and early flowering) because they caused significant visual injury, height and yield reductions (Table 2).
Table 1. Application window for post emergent broadleaf herbicides in soybeans.
| Herbicide | Application Window |
| Basagran Forte | unifoliate to 2nd trifoliate |
| Classic + non ionic surfactant + UAN | 1st to 3rd trifoliate |
| FirstRate + non ionic surfactant + UAN | prior to flowering |
| Pinnacle + non ionic surfactant + UAN | 1st trifoliate to pre flower |
| Pursuit + non ionic surfactant + UAN | up to 2 leaf weed stage |
| Reflex + Turbocharge | 1st to 2nd trifoliate |
| glyphosate1 | until flowering |
1RR (glyphosate tolerant) soybeans only
Table 2. Injury, height reduction and yield of soybean following applications of post emergent herbicides applied at twice the maximum labelled rate (overlap rate) and between the 5th trifoliate and early flowering stage of soybean.
| Herbicide | Injury(%) | Height Reduction (%) | Yield (bu/ac) |
| None | 0 | 0 | 56 |
| glyphosate1 | 2 | 3 | 54 |
| FirstRate + Agral 90 + 28% UAN | 11 | 13 | 56 |
| Basagran Forte | 10 | 2 | 56 |
| Classic + Agral 90 + 28% UAN | 13 | 12 | 54 |
| Reflex + Turbocharge | 13 | 2 | 55 |
| Pursuit + Agral 90 + 28% UAN | 26 | 19 | 50 |
| Pinnacle + Agral 90 + 28% UAN | 47 | 28 | 51 |
1RR (glyphosate tolerant) soybeans only
Source: Three trials, Dr. P.H. Sikkema, University of Guelph (2007-2009)