A grass herbicide did not control a plant with yellow-green triangular stems. What is the likely reason?

The presence of yellow-green triangular stems indicates that the plant in question is yellow nutsedge, which is a sedge and not a true grass. Grass herbicides are specifically designed to target and control grasses; therefore, they are ineffective against sedges and broadleaf plants. This classification is crucial because sedges, like yellow nutsedge, have different biological characteristics and growth habits compared to grasses, which require different types of herbicides for effective control.

In this scenario, the herbicide in use is not formulated to impact sedge species, resulting in a lack of control over yellow nutsedge. Recognizing the biological differences between grasses and sedges is essential for selecting the appropriate herbicide for effective management.