Where pre-emergent herbicides have been applied, a light cultivation now will remove emerging weeds, and give an opportunity for herbicides to work. In soybeans the optimum timing of harrowing is generally 7-10 days after planting before weeds are visible. Weeds which emerge with the crop are much more competitive than later emerging weeds. The critical period to keep soybeans weed free is from the 1st to 3rd trifoliate stage. In a Roundup Ready program or conventional herbicide program, control weeds by the 1st trifoliate stage to prevent any yield loss.
Broadleaf weeds are much more competitive than are grasses.
For example, it takes about six foxtail plants to reduce yields as much as one lambsquarter or pigweed. Wet and windy conditions will favour the spread of disease in wheat. Tilt provides about 3-4 weeks protection, but will not protect against Fusarium. In scouting the wheat, look for disease on the upper 2-3 leaves on the plant. However, don't be confused by light green flecking on the wheat, that is caused by weather conditions.